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What is a Variable Frequency Drive?

Posted by Craig Hartman 20/03/2014 261 Comment(s) Variable Frequency Drives,

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261 Comment(s)

Butch Tan:
22/11/2019, 07:40:14 PM

1)Will i save energy cost if i apply vfd to my pool pump filter? I use 2hp electric motor 12 hrs daily.
2) will i save energy cost if i apply vfd to my main water pump? I use my 5hp water pump aprox 3 hrs a day.
Thank you

19/11/2019, 09:06:11 AM

I was wondering if I could use a vfd on a 110 volt band saw to slow the motor speed , but not loose torque ? So 110 in 110 out Thanks KEN

Taylor Bishop:
27/08/2019, 11:01:33 AM

Thanks for helping me learn more about variable frequency drives. It's nice to know that a VFD help there be fewer mistakes in your motors. I'm interested to learn if a VFD can work with any type of motor. http://cernex.com/cernex_products.html

22/08/2019, 10:31:29 PM

Good article, that is well explained. Thank you

19/08/2019, 09:56:14 AM

I am looking for a vfd for a heat wheel. which ramps the motor up or down as the humidity is present. Which vfd should work for this application.
My motor is 1 h.p. 3 phase.230 volt 3.1 amp..
Thank You

Anthony Redmon:
19/08/2019, 09:38:54 AM

I am wanting to run a 3 phase motor (1.5 hp / 5 amp max) to irrigate a pecan orchard - I have standard 1 phase service - can a VFD convert to 3 phase to run the motor at capacity or am I better off finding a rotary convertor? If a VFD will work what size (or specs) will I need?

07/05/2018, 04:29:24 AM

May i ask where can i find or where can i get the set point of the speed control based on supply duct static pressure of AHU VFD's. Thanks a lot.

01/05/2018, 04:59:29 AM

Than for your for your information

jan malesela:
28/04/2018, 08:31:15 AM

good discussion about vfd

16/04/2018, 09:45:55 AM

Very nicely explained about the VFD working in ac motor

07/04/2018, 05:22:23 AM

it is good information

16/04/2018, 06:55:30 AM

yes its very good information. i like your thinking very much,

ken hite:
04/04/2018, 06:17:29 PM

can i use a vfd to regulate a single phase motor as well ???

Yin (Admin):
09/04/2018, 03:34:48 PM


We are not aware of any VFDs made for single phase motors. Your best chance is to get a three phase motor.

Mark ernest mendoza:
15/03/2018, 01:11:28 AM

Sir if my supply voltage is 400v 60hz and the supply voltage for a certain motor is 460v 60hz, could i use a vfd just to compensate the 460v requiremebt of the motor?

Yin (Admin):
26/03/2018, 03:57:32 PM


You can try using your VFD but it will likely run into over current issue at full speed (60Hz). The proper way to fix this is to either get a transformer to boost your incoming voltage to 460V, or find a 400V motor and pair it with a VFD. Most VFDs can be run at 380-480V. Hope this helps.


Jah Lord:
06/03/2018, 08:11:47 PM

A very straightfoward way to explain the VFD electrical theory principle!

Thanks a lot!

sricharan reddy:
05/03/2018, 10:36:46 AM

this is very knowledgeable matter to learn the about VFDs.
thanks for the given information

05/03/2018, 01:15:33 AM

It is good basic concept explained

14/02/2018, 12:44:06 AM

This is good teaching

13/02/2018, 06:52:38 PM


fredrick Ewiwilem:
12/02/2018, 02:35:32 PM

thanks for your simplicity of language and explanation. well understood.

Lekkala Sudheer:
09/02/2018, 08:24:47 AM

How can I control my DC motor speed

Yin (Admin):
26/03/2018, 03:58:21 PM

Hi Lekkala,

You can purchase a DC VFD.


06/02/2018, 09:00:23 AM

I am from India. I have a VFD 90kW in my factory for controlling a compressor. Recently the line input reactor completely burnt (All the 3 phases) and also the reactor's core got welded with the panel board and the 2 input line fuses of 250 Amps blown out. We are not able to find the reason for such a huge failure. Now the condition of the VFD is if I apply input 415 VAC 3 phase, the drive switches ON and the display of the drive's operators panel is also in ON condition. I called a power electronic service person and inspected the VFD, he said the VFD is not having any shorts between the 3 phase AC input and the DC bus. Also he told there is no shorts between DC bus and 3 phase output of the VFD. Also in my VFD panel the 3 phase power line filter also got damaged.

Now I have placed order for the same type of reactor, replaced the fuses and the 3 phase power line filter. I would lie to now whether I need to check any insulation resistance between the VFD input 3 phase terminals and body of the VFD also the same for the output using megger of 500V. I tested the resistance between the 3 phase input and body of the VFD and the same for the output using a Digital multimeter (DMM), I am getting only 3 to 5 meg ohms, is that fine ?. But I have not tried anything with megger. Kindly let me know why the Reactor failed and what may the cause of failure. Kindly help me by sending me the above details, to avoid such breakdown in future.

Thank u for spending your valuable time reading my message and for replaying.


31/01/2018, 07:53:04 AM

May I know if there are any Advantages if I go for a oversize VFD drive, My motor power is 1/2 HP

Yin (Admin):
21/02/2018, 11:18:41 AM


Going with a bigger VFD will allow you to have the flexibility to use it on bigger motors in the future, and your VFD will not be running as hot because it is not using its full capacity. Hope that helps!


Akhilesh kumar:
28/01/2018, 03:49:47 AM

It's good to know about vfd.you can also add in it torque relationship.as we need to consider torque in many application s.like lifts ,pumps etc wIth respect to speed

Naushad Usmani:
26/01/2018, 04:54:36 AM

it is very useful information
Thanks I learn a lot.

22/01/2018, 06:27:13 AM

good staff but l nid more explanation on those six diodes

02/01/2018, 04:42:18 AM

just for clarification. is the term OPEN here is no current or has? it confused me a bit due to your plumbing comparison . TY

30/04/2018, 12:55:15 PM

Open refers to no current flowing. Closed refers to current flowing

15/12/2017, 10:59:13 PM

How are you,
Dear sir how can I get more information about vdf in need to know more about vdf systems am an electrician

Shailendra singh:
14/12/2017, 06:11:13 PM

Very knowledgeable and good information about vids.

Sudhir patil:
20/11/2017, 07:49:06 AM

If speed decrease with VFD, does torque increase?

Usman Sharif:
20/11/2017, 05:23:58 AM

It is very useful information.
Thanks i learn a lot.

Usman Sharif:
20/11/2017, 05:23:55 AM

It is very useful information.
Thanks i learn a lot.

10/11/2017, 03:49:16 AM

Hu sir, Good evening all, we are dealing with scrubbers and waste water treatment systems. In our Scrubber system WE NEED TO CONTROL THE SUCTION FAN(CENTRIFUGAL) SPEED BY OUR 4-20 MA FROM THE MASS FLOW METER USING – VARIABLE FREQUENCY DRIVE(VFD). So please advise our queries below,

1. Is it possible to control the fan speed with our 4-20ma Mass Flow Meter signal using VFD ?
2. Can VFD have the provision to connect our 4-20 ma ?
3. What methods/Signals required, Normally to control the fan speed using VFD
4. Please Attach their detailed brochures
5. And factors to consider for selecting your VFD

Thank you and looking your Expertise advice asap please.

Drew (Admin):
10/04/2018, 10:03:07 AM

Good questions! I’ve replied in order:

1) Yes. VFDs are designed to control the speed of your electric motor in order to better suit the application you are using it for. You can program your VFD to run at different speeds for different mass flow meter(or other devices) readings.
2) Virtually all current VFD models can accept a 4-20 mA signal.
3) VFDs can use a variety of different signals, from a variety of different sources. While 4-20mA is a very commonly used, there are many others such as 0-5V, and 0-10V, just to name a few.
4) When selecting a VFD, you need to first ensure that it will accomplish what you need accomplished. Beyond that you’d be looking for one with a good cost/value ratio. Our drives are competitively priced, have great longevity and a have a variety of features to help your operation run efficiently.

aseel Al-sinayyid:
07/11/2017, 02:01:50 PM

It is very useful information
I want to ask about some types of vfd devices they have inductor (chock) after the rectifier why? what is it doing?

04/11/2017, 02:21:20 PM

Thank You very much for a nice & useful interpretation about VFD function. I am grateful to You. We the readers have more requirements as we are not pre experts & professionals in this sector. So I am expecting if it is possible to explain the function of each components of VFD by visualizing in Oscilloscope when the Motor is running (controlling the speed) (conversion of AC-DC-AC, Diode function, Capacitor function, Magnitude of AC & DC Voltage, Changing Frequency & current etc.). A 3 phase Motor is running by VFD. How I will measure the variable(instentenious) frequency as well as voltage ? As far I know, Power(P)=Torque(T) X RPM. Three situations can be happend (1) T is constant RPM is variable. (2) RPM is cons. T is variable. (3) Both are variable. How these three situations are handled by VFD ? If it is possible please explain.

27/10/2017, 08:37:50 AM

I am using a 55 kw motor and the motor is controlled by VFD. The full load current of motor is 88 A. The warning current is set at inverter as 98 A. But inverter is trippng for load current of 71 A itself and alarm message comes as "overcurrent". Can you please help?

31/03/2018, 11:28:17 PM

The problem is CT (current transformer) u calibrate the ct output

18/10/2017, 07:20:33 AM

Wonderful information, big ups!!!

mohamed shaban elhamshary:
16/10/2017, 06:14:26 AM

we have a motor with speed from 875 to 985rpm,the speed of this motor controlled by VFD.

the speed from 960rpm to 990rpm, there is a noise appeared in the motor below this speed there is no noise.

could you please help me to understand where is the noise coming?
what is the effect of this noise in the motor?


Mohammad Ali:
15/10/2017, 06:10:33 AM

Help full details

Gurvinder Singh:
02/10/2017, 09:33:42 AM

We need a vfd for 20Hp 2 pole motor for centrifuge to run between 1000 to 3000 rpm

Terra Agrobiotech ltd:
29/09/2017, 08:32:50 PM

We need a VFD for our plant for fertiliser so please send your quotations or help us in other way which is convenient for you .

26/09/2017, 11:44:03 PM

Help full

Faisal inam:
24/09/2017, 03:23:23 PM

There is very useful information . I learn a lot. Thanks

amer sami:
24/09/2017, 01:21:30 PM


can I put vfd system faraway from motors 50 meter or nearest its better and what different

thanks for help

22/09/2017, 02:53:56 AM

Good information about vfd

Ranjith saravanan:
18/09/2017, 08:05:39 PM

Good Information

Vishwanath G G:
16/09/2017, 12:20:37 PM

Dear Sir,
Your blog is really informative. I am trying to understand VFD and its application on a EOT hoist. I am interested to know: "By any means , is it possible to use vfd voltage or current ratings to detect if the hoist is holding a load or not ?" .......... Any information provided by you would be helpful and shall provide me directions to learn better....

Harold Aaron:
12/09/2017, 03:20:09 AM

I couldn’t resist commenting. Very well written!

Derrick Muhandia:
08/09/2017, 07:45:51 AM

To start the drive en run a motor during parameter entry and savings how can u ensure u work efficiently as a first time practioner

01/09/2017, 02:36:02 AM

we are using a vfd, when we increase the frequency upto 37 hz, it is working fine.if we increase above 38 hz the voltage will raise upto 670v between phase to phase & vfd trips.
what may be the problem, please suggest.

Thanks & regards,

30/08/2017, 12:15:50 AM

Sir, I have to convert my shaft speed from 1400 rpm to 10 rpm. Which VFD I must use and what would be the cost of it.

31/03/2018, 11:36:34 PM

1.The selection of vfd is based on motor kW rating
2.all vfd possible to control speed from zero to synchronous speed
3.the price depends on kw rating

30/08/2017, 12:15:48 AM

Sir, I have to convert my shaft speed from 1400 rpm to 10 rpm. Which VFD I must use and what would be the cost of it.

Robert Sheppard:
05/10/2017, 01:00:18 AM

Use a reduction gearbox

26/08/2017, 02:47:05 PM

Variable frequency drive where is the use..

05/09/2017, 01:45:39 PM


fasika sisay:
07/08/2017, 08:52:48 AM

hi sir
if we adjust the VFD in 25HZ what will be the output voltage in the motor.is this formula working to calculate the voltage Vo=vt/ft*fs
where vo is out put voltage
vt is total voltage or supply voltage
ft is high frequency 50hz
fs is set point frequency. thanks.

21/07/2017, 05:36:51 AM


20/07/2017, 07:27:00 AM

Sir ...
We have 100 hp motor with fluid coupling.. and I want to replace Fluid Coupling to vfd . So what to do...

20/07/2017, 07:27:00 AM

Sir ...
We have 100 hp motor with fluid coupling.. and I want to replace Fluid Coupling to vfd . So what to do...

20/07/2017, 07:26:59 AM

Sir ...
We have 100 hp motor with fluid coupling.. and I want to replace Fluid Coupling to vfd . So what to do...

20/07/2017, 07:26:43 AM

Sir ...
We have 100 hp motor with fluid coupling.. and I want to replace Fluid Coupling to vfd . So what to do...

20/07/2017, 07:26:39 AM

Sir ...
We have 100 hp motor with fluid coupling.. and I want to replace Fluid Coupling to vfd . So what to do...

Engr. Hassan Jawaid Athar.:
18/07/2017, 11:23:42 AM

Very very Good, and very informative.

13/07/2017, 04:58:51 AM

Two lifts with 7.5 HP Moters and 11 Kw VFDs to control their operations. THE MOMENT WE SWITCH ON THE the system system trips . Can we be helped

himanshu mali:
11/07/2017, 09:50:44 PM

can we control three motors connected in parallel from same VFD?

jyoti verma:
07/07/2017, 12:34:58 AM

by varying voltage and frequency applied to motor ...but practically ve are changing only frequency cupply voltage will be constant whether 3 phase or 1 phase . I m not getting the efinition

02/07/2017, 12:54:31 AM

Hi. I replaced my wood lathe motor with a Hitachi 2HP/3PH motor rated at 200V and 6A FLA at 60 Hz. I am now shopping for a proper 1PH input/3PH output VFD with the proper specs.

1. Can I independently control (while maintaining the Hz I want) the VFD 3PH output to not exceed 200V? Or is applying 220V output still safe for the motor even in the long term? As mentioned, my expected motor loads will always be light to rarely medium.

2. Considering the lathe's light duty, I was hoping that a 3HP VFD will do the job?

3. Will the 200V rating have any issues with the FWD/REV function?

Thanks... Rico

B. Southard:
16/06/2017, 09:20:54 AM

Question: I am working on a stock water pipeline. The well will also service some corals and a residence. A 3 hp pump will be required to run the system and pressure reducers will be placed on the coral and residential lines. The problem is that static pressure from the stock water line is about 150 psi at the well. Can a VFD handle that kind of static pressure? Thanks for your input!

Bijay Kumar sawayan:
16/06/2017, 08:19:30 AM

Yes this is a perfect application

chikku raveendran:
11/06/2017, 11:36:55 AM

i have a problem with VFD in my HVAC unit its often showind DC bus over voltage in its HMI, what could be the possible reasons and can u suggest a solution for this.

and after 10 - 15 minutes of running it will get automatically shutted down.

Connor (Admin):
13/06/2017, 02:37:31 PM

I'm sorry but I'll need more information in order to properly suggest a solution. Give us a call at 1-800-800-2261.

Virender Singh:
08/06/2017, 10:55:35 AM

We have 180hp/2900rpm/3phase motor which runs centrifugal air blower at 160amps in normal conditions but sometimes we have to run this blower at lower flow rate by throttling discharge valve, can we use VFD, if yes what should be the specifications of VFD to float purchase inquiry. Thanks

Connor (Admin):
13/06/2017, 02:10:43 PM

Yes, this is a perfect application for a VFD. Based on the provided specifications, the FR-F840-01800-3-60 would be a good fit. If you want to double check everything give us a call at 1-800-800-2261.

mahadev dandge:
01/06/2017, 10:55:47 PM


Dinesh Mana:
18/05/2017, 03:18:24 AM

how can i measure output voltage from ac drive with multimeter

Connor (Admin):
25/05/2017, 02:23:31 PM

On the drive you'd connect the multimeter to the screw terminals correlating to the output voltage.

16/05/2017, 10:30:38 PM

My Motor full speed is 995 rpm ( 415V, 50 Hz ), Can I increase the speed to 1100 RPM?
With VFD can we increase the speed of the motor beyond the stated RPM in the motor rating plate?

Connor (Admin):
25/05/2017, 02:29:58 PM

Yes. You'd want to raise the max input Frequency to ~55.28 Hz. With VFDs you can increase the speed of the motor beyond the stated nameplate RPM value, but you do lose some torque when doing so.

07/05/2017, 10:49:57 AM

good note

27/04/2017, 10:49:41 AM

I like ur demonstration,


25/04/2017, 06:54:13 AM

Say you have a VFD with a single phase input (generating 3ph rectangular wave form at output) vs a VFD with a real 3ph input. Am I to assume the second VFD will generate a true 3ph sine wave at output, or still rectangular like in the case of 1ph input? In any case - practically speaking - would I see a difference in the way the motor is running? Smoother, quieter, less whistles and whines?

Yin (Admin):
25/04/2017, 11:33:33 AM


No, there won't be any differences. It will generate a sine wave at output. VFDs are often used as a method of phase conversion. Sometimes it is cheaper than a phase converter (usually smaller HP/kW), sometimes it isn't. Hope that helps.

Muhammad Ashfaq:
24/04/2017, 07:28:01 AM

Can VFD be used for reactive power compensation? IF so, how?

Yin (Admin):
24/04/2017, 09:07:48 AM

To our knowledge, it can't.

Kumar Rayanapati:
12/04/2017, 10:12:34 AM

How can I install the VFD for my domestic and commercial use
R.Kumar.Hyderabad, India

Yin (Admin):
13/04/2017, 09:03:33 AM


Each product manuals provide installation guides. After you connect the power cables, you need to program your VFD, which is different in every brand. We strongly recommend you to hire an electrician to install this for you if you have no experience in installing VFDs.

Muhammad Abdullah:
07/04/2017, 06:19:43 PM

Very important information about VFD

Reuven Gomes:
30/03/2017, 03:53:04 PM

Hey guys, I want to buy a 30 hp Nema D electric motor for a research project in my lab. The Locked Current is 213A @ 460V and full load current is 38A @ 460V. My lab power supply is 100A and 230V. The motor can also run on 230V. I have the following questions:

1. Will my motor run on the power supply in my lab?

2.What king of VFD would I need based on my motor specs and power supply?

I would really be very grateful for any advice. Thanks!

Yin (Admin):
31/03/2017, 05:19:30 PM


What is your motor's full load amps (FLA) at 230V?
What kind of application is your motor running?

Reuven Gomes:
01/04/2017, 03:29:06 PM

Hi Yin,

I'm not sure. Since the FLA @460V is given as 38A, @230v it should be 76A right? I'm not completely sure. The dealer I'm buying it from said the fuse chart shows 98A @ 230V for the 30 hp motor and 60A @ 230V for the 20hp. So is that the FLA?

Also, the motor is being used to drive another engine called an optical engine on which I perform tests. It is a large diesel engine, a cummins VT-903. 4 cylinders have been cut off and we inject different fuel into one of the remaining two of which one cylinder has no compression(holes made in the head) so it just helps balance the engine. So essentially, this motor has to start rotating the engine from rest and maintain a speed of 600rpm. I need a VFD to just manually control the speed. A friend of mine using a 10hp motor for an identical application except his engine is a Ford Mustang v8(whole). No compression in 7 of the 8 cylinders though. He is using a Mistsubishi D700 VFD.

Yin (Adam):
03/04/2017, 09:40:51 AM


Theoretically yes, if it is 38A at 460V, it should be 76A at 230V. That is the FLA. It should show on your motor nameplate also.

So the D700 only goes up to 10HP, and the E700 goes up to 20HP. For a 30HP, you will likely need to go to the F800 series. Check out this one FR-F820-00930-3-N6.

Are you making your own electric car? Is space a concern?

Reuven Gomes:
03/04/2017, 10:59:06 AM


I have contacted the motor agent to ask what the FLA is on the nameplate.

And no, I'm not making an electric car. Like I said, it's basically coupled on another engine and rotates it since the engine cannot sustain itself on the combustion tests. The combustion we test for is too weak and just for research. So to answer your question, no, space is not an issue. I'm just going to set up on my table next to the PC.

Are there any cheaper alternatives to the Mitsubishi VFDs? My friend said that they are one the easiest to operate and that's why he bought that one but he got it much cheaper on ebay. Do you have any suggestions? I need it to be able to handle the motor and to be easy to operate. I'm not automating it. Will manually enter the speed each time. Also, it's going to be in a lab and hence not subjected to any harsh environmental conditions.

Yin (Admin):
03/04/2017, 11:11:07 AM

Ok I see. Mitsubishi is quite user friendly, and very reliable. Your friend's drive is much cheaper because it is a micro drive, and it is only 10HP. There are a couple of less expensive options we can look at. Can you send me your contact number to ytang@vfds.com and I will give you a call today?

Michael Drackley:
28/03/2017, 12:49:09 PM

I liked the video, informative and gets to the point!

Babila FONYUY:
28/03/2017, 08:04:19 AM

Hello team, I was asked to carryout a little project. That will consist in simulating a VFD (0.4 kw/0.5 Hp:200-230V (input current 5.5A output 2.5A))with a 3 phase electric motor. Please i wish to know what accessories to use for such simulation. Like type of cable, relay,switch, plug etc....

Yin (Admin):
28/03/2017, 09:17:11 AM

Babila, I am not sure what you mean by simulating. If you want to connect a VFD, you just need 3 cables for the input, and 3 cables for the output. You can learn how to do that here: How to wire a VFD

Somu Raj:
21/03/2017, 03:17:29 AM

I need to know that V/HZ ratio, so the Drive itself will automatically maintain the ratio when we set the frequency or the voltage should be also set by us.
I have some more question, will add up when you reply me.....

Yin (Admin):
21/03/2017, 12:29:35 PM

Somu, I don't understand what you are asking. Can you rephrase your question about the V/Hz ratio?

jyoti verma:
07/07/2017, 12:53:04 AM

VFD with sensor or sensorless have two control method 1) Scalar control 2) Vector control . In Scalar control we follow V/f method while in Vector Control we follow DTC ( DIRECT TORQUE CONTROL ) and FOC (FIELD CONTROL ). somu if u r using VFD might u have set parameter regarding MOTOR CONTROL MODE ( vector speed, vector torque and scalar frequency )u have to set parameter according to your appication.
For ex : i m using 1hp induction motor for filling conveyor for that i m using 1hp ABB DRIVE (MODEL ACS355) as in my application there is no load in conveyor ( filling purpose) so i m setting PARAMETER 9904 equal to 3 that is SCALAR CONTROL (V/F CONTROL)

Hope u understand this if any issue revert back...

20/03/2017, 02:17:55 AM

hello sirs,

what type of vfd could be used for drag conveyor to lower the Motor rpm but "increasing/maintaining the torque"?

(note; the said drag conv. is next from its feed screw w/ fixed rpm so lowering drag rpm/speed will increase the load to the motor,the purpose of reducing rpm is not to reduce mat'l flow but to increase mat'l bed level for efficient machine operation). the drive assembly is 3hp 440v 60hz 3ph 1780rpm motor coupled w/ 3 reduction gearbox units to achieve lower speed range,the first gb has variable speed adjuster previously where we reduce the speed but it was broken so i suggest to replace it w/ fixed rpm and install vfd to the motor.

Yin (Admin):
20/03/2017, 04:11:19 PM


You will need a VFD that is constant torque (CT), meaning it has at least 150% overload rating. Mitsubishi makes a great constant torque VFD, and that is the A840 series. Size your VFD based on your motor amp rating, make sure the VFD has a higher maximum amperage rating.

03/03/2017, 12:44:52 PM


Can we tell one vfd is in good working condition by only measuring voltage at output terminals of vfd ?

While measuring output Multimeter should be in DC mode or AC more ?

When we increase the frequency in control unit, output voltage at vfd will increase or not irrespective of motor is connected or not ?

We are using sew eurodrive.where can i get troubleshooting manual for this?


Jeff Condit:
08/03/2017, 04:21:00 PM

Comment No, basic VFDs do not reduce the peak voltages and so a voltmeter will not be accurate. Instead, they spread out a series of pulses alternating a group of positive ones then a group of negative ones. The overall duration of the positive and negative pulses combined is the effective period of the VFD. If you have to measure it you would be better to use an oscilloscope if you have one. Otherwise you could make a filter out of an inductor and a capacitor to help smooth out the pulses and see the overall period. Remember, the inductance and inertia of the motor smooth out the pulses coming from the VFD to make relatively smoother motion at a slower frequency that if the motor were run directly of the line.

(NOTE: It is also possible to synthesize a frequency higher than the line frequency.)

Yin (Admin):
20/03/2017, 04:24:01 PM


Some good indicators that show the VFD is in good running condition: (1) no error codes displayed on the LCD screen, (2) the VFD is operating at programmed speed, (3) no strange noises, and no visual dirt or water on the VFD, (4) the VFD is running under the maximum operating temperature - typically below 110-120°F.

You measure in AC if it is an AC inverter/VFD.

The voltage will not increase when you change the frequency/speed.

For manuals, you will need to go to the manufacturer's website. Their support/resource page will have all the documentation you need.

Hope this helps.

02/03/2017, 10:01:17 PM

I am using 2 HP 3 phase ac motor to rotate a 8 kg circular shape cutter mounted on motor shaft. I want to control motor speed such that it will run at constant set speed at the time of cutting action. I used dimmerstat but speed of motor reduced during cutting action. If I use vfd, can I have constant speed as required for my application?

Jeff Condit:
08/03/2017, 04:09:54 PM

Dimmers do not tightly regulate motor speed under varying load. They merely apply less voltage. By the time you've starved it enough to slow down, it my well stall out altogether.

A VFD is different than a dimmer. They chop the signal to make it "look like" the frequency is lower. So to the extent the motor keeps running under such reduces power conditions, it will run more slowly.

Yin (Admin):
20/03/2017, 04:14:01 PM

Yes Mayur. The biggest purpose of a VFD is to maintain and control speed.

George Alai:
16/02/2017, 08:42:48 AM

Good evening,I'm A technician by profession. Just the other day VFD for cane belt conveyor fuses exploded while in operation, what could be the problem?

Jeff Condit:
08/03/2017, 04:33:48 PM

Comment There could be any number of problems. But assuming everything remained in good working condition and this occurred there is a concept which comes into play and should be noted: Fuses open because they melt. they melt because they get hot. They get hot because they have some resistance and the current through it creates a voltage drop and hence power loss. The power lost at any instant goes like P=I^2R. So if you change a slowly moving signal like the AC line into one which toggles between off half the time and twice as big the other half, then the average would be correct, but the Power dissipated in the fuse would be nothing during the off half and 4 times as much during the on half. Hence the average overall heating in the toggled case is twice as much. Hence a fuse would blow at half the current in such a case.

Yin (Admin):
20/03/2017, 04:14:43 PM

George, how long has the VFD be operating with the conveyor?

jyoti verma:
07/07/2017, 01:49:21 AM

george fuse how much amps?? if u r using VFD i don think u have to use fuse for it

10/02/2017, 09:53:18 PM

I am confusing beffor see this article. Now I am understood that how vfd work.
Thanking you

05/02/2017, 06:41:11 AM

I am sure that there won't be any adverse effect eg. being inductive?

02/02/2017, 06:38:51 PM

Dear Sir,

AHU motor encounter incoming phase unbalance problem.
Incoming L1,L2,L3 current 60A, 40A, 60A to VSD outgoing current was balance and VSD was not trip.
May I know whether VSD was at fault???
Please advise.
Thank you in advance

Yin (Admin):
03/02/2017, 02:06:57 PM

What is your voltage and the maximum amps of the drive? What is your VFD model?

Gerald Zimba:
02/02/2017, 08:53:10 AM

hi,i have an iron roller press laundry machine,the vfd displays an error code cf3,and the motor stops after some time it starts, what does the error code mean, and what makes the motor to stop. I v had this problem for a long time I will really appreciate. thank you in advance

31/01/2017, 09:57:39 PM

I am electrical technication I want to know that what requirement we need to set a vfD Into a motor.I am using alitvar 31 telemecanique VFD.where I get the basic troubleshooting programs

Yin (Admin):
01/02/2017, 01:15:11 PM

Hi Lino,

I am not entirely sure what requirements and troubleshooting programs you are asking for. If you are looking to size a VFD, please check out the VFD Buying Guide. If you are looking for programming instructions, here is an example video for the Mitsubishi VFD.

25/01/2017, 07:26:10 PM

Ok I am a little lost on the capacitors? If they are in a DC circuit, wouldn't the electrons just collect and stay put? Or is the opening and closing of the switches on the inverter enough of a potential voltage change to release electrons?

Yin (Admin):
01/02/2017, 04:40:21 PM


Sorry it took us a while to respond. I have discuss this with 2 engineers, here is our answer. I hope it helps you further understand the VFD construction.

It is best to think of this as electrical energy rather than electron flow. A capacitor in an electrical circuit acts like a tank in a plumbing circuit. As current flows into the capacitor, the voltage increases. This is analogous to the level of the tank getting higher as you add more water. Thus, the capacitor stores energy just like a tank stores water. When the voltage on the dc capacitor reaches the peak voltage on the incoming ac source, then the capacitor stops charging. This is just like filling a tank with a hose. When the tank level gets high enough, the pressure in the tank will equal the pressure in the hose and no more water will flow.

The purpose of the converter (6 diodes) is to add energy to the capacitor. When the inverter (6 transistors) needs energy to send to the motor, it gets this energy from the capacitor. So all energy for the motor comes from the capacitor and the converter re-charges this capacitor as necessary to keep it close to full voltage.

sudershan prasad:
15/01/2017, 06:39:14 AM

Benefits of line reactor drive input site or out put site what benefits

Yin (Admin):
17/01/2017, 05:02:29 PM

Hi Sudershan,

Please check out our 3 articles about line reactors, that should help you understand the benefits!

What is a line reactor
How will line reactors help your VFD
Why should you use a line reactor

haris pervaiz:
12/01/2017, 10:10:43 PM


Yin (Admin):
13/01/2017, 09:05:01 AM


No, it will not. If anything, running at 45Hz will actually extend the life of the motor because it will not be running at full speed. Theoretically, it will have less mechanical wear and less deterioration caused by heat. Hope that helps.

daoui elmaati:
12/01/2017, 01:32:48 PM

hello, we have VFD D700-sc for puping water with solar energy and with an automatic system.
the problem is when the tank is empty the system does not work automatically.the VFD shows a message like this E.0u3. I dont know what does that mean? please can you help us?

Yin (Admin):
12/01/2017, 02:01:11 PM


The error code E.0u3 refers to regenerative overvoltage trip during deceleration or stop. Here are a few possible solutions:

(1) Increase the deceleration time
(2) Increase the brake cycle
(3) Use regeneration avoidance function (Parameter 882, 883, 885, 886. See manual page 226, Section 4.20.3 for explanations)
(4) Add a brake unit on your VFD

You can find this particular error code explained in page 254 of your full instruction manual. Hope that helps.

12/01/2017, 12:30:35 PM

Dear Sir,

I have a pump motor 2.2 kw -3000 r.p.m. I want to decrease r.p.m. to 2500 r.p.m so the pump
by VFD power will decrease from 2.2 kw to 1.2 kw can I use VFD of 1.5 kw for that purpose ?

Thank you in advance.

Yin (Admin):
12/01/2017, 01:54:34 PM

Hi Youssef,

No, you cannot. When you choose a VFD, the VFD amps must be equal or higher than the motor amps (FLA). Your running speed should not be a determining factor of sizing the right VFD for your motor.


Sai Srinivas Desabathina:
09/01/2017, 07:26:32 PM

Hello Mr. Craig,

YOur videos and texts have been of immense help. Thank you. I have a question for you. Do these VFD's work with a single-phase induction motor. I have a single phase induction motor ( capacitor start) which I have been operated at constant speed. To meet my present applications I need to vary the speed of the motor. Is it possible to use the VFD to control the speed of the single-phase induction motor.

Thank you

Yin (Admin):
12/01/2017, 01:52:37 PM

Hi Sai,

Yes, you can use a VFD to control the speed of single phase AC electric motors. Most VFD manufacturers make single phase VFD in 230V class up to 3HP. For example, Mitsubishi has the D720S series for single phase motors. When you choose a VFD, you should make sure the VFD amps is higher than the motor amps.

Hope this helps.


04/01/2017, 06:02:58 PM

What effect on vfd and motor are both different rating installed
Like vfd 40 HP and motor 25hp

Yin (Admin):
05/01/2017, 09:44:43 AM


Generally speaking, that is a good thing. It will work great when the VFD is bigger than the motor. The VFD will not be using its full capacity, and hence it will run slightly cooler.

You will need to check the overload rating of the VFD to see whether it is 110% or 150%. If your application requires 150% overload rating, make sure your VFD is rated for 150% also.

Second factor is if the ambient temperature of the installation is above 100°F or 37°C, you will need to make sure the VFD is bigger than the motor in terms of amps. Whether how much bigger it needs to be, it will depend on the temperature. The process of oversizing the VFD is called derating.

03/01/2017, 10:27:17 PM

Hello Sir,

Assume a six-pulse VFD which is fed by a 400 V line-to-line(rms) ac line. In this VFD, the dc-bus voltage will be approximately, 540 v. It seems that this VFD can not generate 380 v line-to-line rms voltage. (the maximum line-to-line voltage will be 330v!). Is this true? in other words, six-pulse VFD can be used in 400 v grid to drive 380 v motors? in this condition, which kind of VFD should be used?
another question is that in six-pulse VFDs, over modulation for PWM-inverter is legal(in order to achieve increased voltage level in ac side?

Yin (Admin):
04/01/2017, 10:40:44 AM


VFDs have a voltage range. Typically 230V class has a range of 200-240V and 460V class is 380-480V. You can use these drives as long as your input voltage is within the range.

Regarding which drive to use, as I have responded to your other question, it depends on a few things, such as the motor amps, the type of machine (application), power supply, environment, etc. Without all the information, you cannot determine what VFD should be used.

I am not sure what you are asking in your last question about PWM.

10/01/2017, 09:38:48 PM

In the sample VFD in this page, assume that the input voltage is 400 v. Thus the dc-bus voltage will be: 1.35*400=540. It means that the maximum peak-to-peak voltage in the ac side will be 540. So the maximum peak voltage of each phase in ac side will be 270v. By this, the maximum achievable value for rsm voltage of each phase can be: 270/1.41=191v.
However, in order to generate 400v line-to-line voltage in the ac side, the rms value of ac phase voltage should be 230v,(191<230). Can you help me in this regard?

Yin (Admin):
12/01/2017, 05:31:34 PM


Assume input voltage is 400V. The 1.35 figure is an approximation. When the motor is off, the dc bus voltage will be (SQRT(2)) x 400 = 566V. As you load the motor, the voltage will begin to drop. When the drive is loaded, the dc bus voltage will be approximately 1.35 x 400 = 540V. The output voltage is a series of pulses. Although the peak of the voltage on the output is 540V (as opposed to 566V for a sine-wave), a 400V rms signal can still be generated by shaping the waveform. It is typical to use 400V rated drives (with 400V on the input of the drive) to provide a 380V output for 380V motors. When the output is programmed for a 380V motor, a 380V line-to-line voltage will be generated (not 330V).

The voltage on the output of a VFD cannot be higher than the voltage on the input, but it can be the same. The previous statement is not 100% true, but it is true for all larger industrial drives. Trying to use special modulation techniques to increase the motor voltage will have deleterious effects on the motor.

Hope that helps!

15/01/2017, 04:09:01 AM

Thanks for your response. Assuming that the input voltage of a six-pulse VFD is 400v, when the motor is loaded, the dc-link voltage will be 400*1.35=540v. If the inverter uses for example Space Vector Modulation, the maximum possible output line-to-line voltage can be:
My question is exactly this, if we are using a six-pulse VFD which is fed by a 400v line-to-line rms voltage grid, can we provide 400v line-to-line voltage in the motor side? or the maximum possible value is 380v?

Yin (Admin):
18/01/2017, 09:27:37 AM


I have been talking to our VP of engineering about your question. He agrees that this is a difficult question to answer since it depends on so many factors such as power system voltage, power system voltage regulation, D.C. Line reactors, ac line reactors, drive isolation transformer, harmonic filter, motor loading, motor lead length, and etc.

For instance, if you have a 6-pulse drive with 5% line reactors, 400V power supply, and the motor is at full load, then you may not get more than 380 to the motor. But, if you put a harmonic filter on the drive, then there is a small voltage rise through the filter and you can get a higher output voltage. Fortunately, 400V power systems use 380V motors, so we seldom worry about getting sufficient output voltage.

02/01/2017, 03:12:28 PM

In Mitsubishi inverter A700 series 25hp show error code err and inverter cannot reset I do all think

Yin (Admin):
03/01/2017, 09:33:29 AM

What is the error code? Is this the drive you are using to run the 2900 RPM motor?

03/01/2017, 10:49:23 AM

No this another drive for different.
Drive fault code :err

03/01/2017, 10:51:51 AM

No drive run on 1400 rpm 25hp

30/12/2016, 08:19:37 PM

No same rating vfd .What perameter for pole change

And I have suggested to you please add photo attached ment with comments in comment box

Yin you are doing wonderful work

Yin (Admin):
03/01/2017, 09:32:59 AM

Hi Ashish,

You are welcome to send us the photos at bdt@emcsolutions.com


29/12/2016, 06:45:47 PM

I have mistubishi vfd
Modal fr-D740-080ec
Input 13.9A output 8.0A
Problem is in drive run 1400rpm 2hp but when we connect 2900rpm drove indicated fault

What is problem

Yin (Admin):
30/12/2016, 09:53:20 AM

Ashish, what is the error code?

30/12/2016, 12:19:32 PM

Show overcurrent ,when connected 2900rpm motor ,1400rpm run without problems,
Mitsubishi vfd have any pole parameters in drive which perameter I changed

Yin (Admin):
30/12/2016, 02:26:30 PM


Check your amps. Make sure your VFD has a higher amp rating than your 2900 RPM motor. It sounds like you need a bigger VFD.

ravi kiran:
28/12/2016, 12:05:31 PM

i am having a 55KW motor used for mixer purpose(constant speed nearly 50hz)and i want to vfd to run.can i save energy by using vfd for this

Yin (Admin):
30/12/2016, 09:58:28 AM

Ravi, you could potentially save energy for a motor at that size. It depends on your run speed, run time, load, utility structure in your area. If you are running at 50Hz, which I assume is full speed for your motor, it is quite unlikely that to save any energy using a VFD. If you are running the motor at full speed, there is probably no need to use a VFD. Hope that helps.

Mukul Mondal:
23/12/2016, 12:41:08 AM

I have one problem of VFD ..I started the motor 30 minutes after automatically stop and there shown phase unbalance fault..how can I solved this problem...

Yin (Admin):
23/12/2016, 12:00:04 PM

Hi Mukul,
You are losing a leg, so the VFD is tripping. Meaning a wire is coming loose somewhere in your system. So check your connections. It is usually the connections at the VFD. If not, check inside the junction box of the motor, or the contactor (if you have one) between the motor and the VFD. Hope that helps!


22/11/2016, 08:30:23 PM

Motor Model : ABB, 415V, Frequency 50hz, Power 90kw, Speed 3950 rpm
Application : Pump
Product : Condensate

Questions : Soft starter procedure using VFD

20/11/2016, 09:21:10 AM

Hi sir,
What is the problem in VFD if in running time its ok but motor stopping time vfd D.C. voltage high and tripped VFD and give the message for reset.

Yin (Admin):
21/11/2016, 03:09:03 PM


What drive do you have?
What is the power setup? (phase, voltage, horse power of the supply power, motor, and VFD)
What is the error code?

26/11/2016, 10:37:48 PM

Dear sir,
I driving centrifuge that is control all data with plc showing on screen. Vfd belongs to yaskawa company.there are two motors in our centrifuge one is main drive motor 150hp.and other is back drive motor attached with gearbox 40hp.
Vfd no :400v.3phase 88A/
Vfd no:400v.3phase 208A/180A
Power 460v ,60hz.
Motor 150HP,40hp
Motor RPM1800
Panel supply output 640,639 dc volts showing on screen. But motors starting time voltage come down at 620,619 like
With control panel 150hp motor rpm 3000.

19/11/2016, 08:23:19 PM

Hi admin
I am having motor of 250 Hp 1400 rpm.If i reduced rpm of motor to 800 by vfd does it will affect the power of motor?

Yin (Admin):
21/11/2016, 03:05:46 PM


What are you referring to when you say "power"? If you are referring to torque, you will not lose torque when you reduce the RPM of the motor.

09/11/2016, 10:41:05 PM

Hi, can you explain to me why overload is tripping when my 160KW motor is reaching it's rated rpm(3,600rpm). I'm using Danfoss VFD aquadrive. I already check my parameters. Thank you in advance.

Yin (Admin):
10/11/2016, 08:56:07 AM

Hi Jeff,

We will need a little more information to go on. Can you tell me the following?
(1) Your motor's FLA
(2) Your VFD's amp rating at 110% and 150% overload rating
(3) What is your application?
(4) Are there any error codes when it trips?

Feel free to respond here or give us a call at 800-800-2261, and let us know you left a comment on the blog. We look forward to hear from you. Thanks Jeff!

14/11/2016, 05:26:10 PM

Hi, (1) My motor's FLA is 222A
(2) The VFD's amp rating at 150% overload is 140 amps
(3) My motor is used as pump.
(4) There are no indicated error in the Control panel display of the VFD.
Thank you for your response.

Yin (Admin):
16/11/2016, 08:20:36 AM

Jeff, a team member of ours have sent you an email. Have you had a chance to send over the motor nameplate info or photo?

09/11/2016, 07:37:33 PM

Thanks and good web page

Givan sagwa:
08/11/2016, 09:59:42 PM

Thanx for the information

Ambaliya meraman:
07/11/2016, 12:15:42 PM

We can use vfd in place of vvfd?

Yin (Admin):
07/11/2016, 02:05:32 PM


I don't think vvfd is a real term. What are you referring to? If you are trying to control the speed of a 3 phase electric motor, you can use a VFD.

Ambaliya meraman , India , , gujrat:
07/11/2016, 12:12:13 PM

Very well information. Thanks

Mateen Uddin:
02/11/2016, 11:02:53 PM

Hi, i want to know that, i have a motors of fixed RPM so in that condition can vfd save the energy?

Yin (Admin):
03/11/2016, 08:34:36 AM


What exactly do you mean when you said "a motor of fixed RPM"?
What is your application?

Mateen uddin:
03/11/2016, 10:58:40 PM

i have a motor for constant speed, so in that condition can i use vfd?

Yin (Admin):
04/11/2016, 08:56:27 AM

Hi Mateen,

Yes, you can. You can use a VFD with just about any 3 phase AC electric motors. Check out the video of how to choose a VFD and let us know if you have other questions. Thanks!

Sunday Adegunna:
28/10/2016, 11:59:46 PM

What is Different between VLF and VVVF and also VFD,
What is advantage and disadvantage of VFD.

Yin (Admin):
31/10/2016, 09:27:08 AM


VVVF means Variable Voltage Variable Frequency, a term more commonly used in Asia. It is essentially the same as VFD.

VLF means Very Low Frequency. It is a particular range of radio frequency. It is not related to VFD.

VFDs are commonly used for speed control, and often a means of phase conversion (single phase to three phase). One of the disadvantages is that it distorts the current and puts out this so called, "dirty power". A line reactor will correct most of that. For more information about maintaining clean power, you can check out this video: VFD Harmonics and power quality.

Hope this helps.

Sunday Adegunna:
28/10/2016, 11:51:56 PM

I really like this lesson and it has help me to understand more about how a motor can be control by VVF.

24/10/2016, 11:27:55 PM

Sir, Some motor manufacturers data sheet have mentioned "Type of starting: Variable voltage/frequency" and some have mentioned "Type of starting: DOL" but they also have written "VFD fed motors" What in diffence in these two motors?
Also explain is there any difference in using VFD for starting purpose and VFD for speed control,are these two related and does it affets motor selection?

Yin (Admin):
25/10/2016, 08:23:33 AM

Hi San,

Any synchronous motors can be powered by a VFD. Newer motors are generally inverter (VFD) duty, some older motors are not. However, our VP of engineer said he has used many motors that are not inverter duty with VFDs and had no problems. From what you are describing, it seems like both are inverter duty motor.

VFD can be used to start the motor as well as speed control, it will not affect your motor selection. Note that you should get a 3-phase AC motor if you intend to pair it with a VFD. I have listed a few videos below that will help you, feel free to check them out!

VFD buying guide

Motor buying guide

How to read a motor nameplate

Khalid Ziad:
12/10/2016, 05:01:02 AM

Should VFD frequency increased gradually until approaching the required speed to run?
or can we set the frequency immediately to the equivalent speed thatwill give and run the motor?
Any side effects?
Because I tried one time to run a VFD motor which is designed at 3600 RPM 60 Hz and I put the frequency 50 Hz to get the 2900 RPM, but the motor was suffering to accelerate to the wanted speed.

Usually I start from low frequency increasing gradually until reaching the frequency I want.

Yin (Admin):
12/10/2016, 04:27:19 PM

Hi Khalid,

Generally speaking, there are no side effects. You can set the VFD to run the motor up to 60Hz in 1 second. The VFD will get there, but the motor might take more than 1 second to get to 60Hz. It depends on the application and its load.

For your specific scenario, what is your application? What VFD do you have? What did you set the acceleration rate at? Is it getting to 50Hz or is it not going past a certain speed?

Animesh Bhowal:
11/10/2016, 07:35:16 PM

Very fine I am enriched from this article

10/10/2016, 08:49:50 PM

Hello if I use a motor that produces 237kW and 17000Nm torque at 127rpm and use a VFD to bump down the RPM to about 3 which is my requirement, will the torque be amplified respectively?

Yin (Admin):
18/10/2016, 10:42:20 AM

Hi Sahil,

The torque will remain constant. However, your motor will likely overheat if you run it at 3 RPM because the motor fan is not spinning fast enough to cool down the motor. We generally suggest not to run the motor lower than 20% of its rated speed because of that reason. I hope this helps!

Shiv shanti petroleum co. Vijapur road, near garden.mansa 382845:
04/10/2016, 02:35:00 AM

98 kw control panel required
Contact no. 9426044445

Yin (Admin):
05/10/2016, 08:42:56 AM

Where are you located?

27/09/2016, 02:41:08 AM

Your comment is 100 % correct but our problem is drive running up to 10.5 Amps(5.5kw) more than 10.5 Amps its immediately tripping ACS550-01-12A-04 we have to go how much drive capable FLA setting with safe running condition. can i know your contact no.

Yin (Admin):
27/09/2016, 08:16:53 AM

Hi Nagula,

Did you by chance see the response I sent to your email yesterday? I don't quite understand your question. You are welcome to call us at 800-800-2261.

22/09/2016, 03:05:03 AM

we are having acs550-01-12a-04 for application is fine coal discharge serew conveyor 5.5kw problem is immediately tripping with overload alarm limited seting is 12.5a replacing vfd to motor and arrange to dol starter running with 10-12.5a why it is not running with vfd.

Yin (Admin):
22/09/2016, 03:16:26 PM

If your VFD does not ramp up at all but trips immediately; you should check your FLA (amps) parameter. You need to set the FLA to match your motor's FLA. If that is correct, check all of your wiring of the VFD. If that is also correct, I would pull the leads and check your motor with a meter. You are having some sort of ground fault or line to line short circuit. Hope that helps!

21/09/2016, 10:31:45 AM

Can two motors be controlled by one VFD controller. Have have both running a the same time??
We have this situation at our water plant. THE VFD of course run warm to hot?

Yin (Admin):
21/09/2016, 10:48:22 AM


Yes, you can with a couple of conditions. You will need a VFD with an FLA (amps) higher than the two motors combined, plus possible derating based on altitude and ambient temperature. The limitation is that you have to start and stop the two motors at the same time with the same setting. If you need help choosing one for your pumps, feel free to contact us at bdt@emcsolutions.com or call us at 800-800-2261.

Ali bedaiwe:
21/09/2016, 09:00:29 AM

appreciate your attention
so if I want to control frequency in an induction heating system (without motor) what can I use

Yin (Admin):
21/09/2016, 11:15:08 AM

Ali, we have no expertise in induction heating system, so we cannot make any recommendations. I would suggest contacting the manufacturer of your system to see what they advice. Sorry we cannot be more helpful.

Ali bedaiwe:
21/09/2016, 08:18:38 AM

very helpful article
can I use VFD for induction heating system ?
If so, is it suitable for for to regulate volt and frequency in the sane time in stead of solid state power controller?

Yin (Admin):
21/09/2016, 08:52:59 AM

If there is not an electric motor in the system, you cannot use a VFD. VFDs are designed for 3 phase electric motors.

20/09/2016, 12:15:32 PM

Very nice

Roly Agbayani:
18/09/2016, 08:46:13 PM

What is the problem if the fuses before the transformer gets busted? it always happen in the Plant on the VFD's for Cooling Tower fans. your advise would be highly appreciated.

Yin (Admin):
31/10/2016, 10:59:09 AM


Are the fuses blowing every time you start the motor? Then you need to have an electrician check all of your wiring. It could be a thousand different things, control wire, power wire, power to neutral, short to ground, cross phase, etc. You need to turn off the power and check everything. Use the method of elimination to narrow down the possibilities. Make sure you follow any safety protocols when you inspect your equipment.

If the fuses are blowing randomly, then you should start by checking your current and see what you are getting.

Ashutosh singh:
18/09/2016, 03:20:41 AM

very good

08/09/2016, 02:48:20 AM

Very nice

John Saunders:
07/09/2016, 04:59:11 PM

Hello - would a VFD be useful when the power supply is single phase 240V 50Hz ... but the motor is a 110V 60Hz one ?

VFDs.com Admin:
08/09/2016, 06:59:18 AM

Hello John,

VFDs output three phase power, therefore, cannot be used on single-phase motors. A VFD rated for 240V input can accept an input voltage of 200-240V at a one frequency, single- or three-phase power, and output the same or different voltage at a different frequency. For example, if you had single-phase, 200V @ 50Hz power, you could use a VFD to supply power to a three-phase, 240V @ 60 HZ motor.

Asim Jan:
03/09/2016, 12:18:33 PM

I have a question what will be the voltage at motor terminals when RPM of motor is zero?
Motor is 37 KW and is connected with VFD made by ABB.

Yin (Admin):
07/09/2016, 08:55:48 AM


When the motor is not running, you should have minimal voltage readings (close to nothing) at the terminals. Be careful when you check the readings, you should always wear proper protective clothing and equipment. Hope that helps.

01/09/2016, 10:50:11 PM

Extremely useful information.

Balikuddembe Ibrahim:
11/08/2016, 03:12:02 AM

Am pleased with this technological innovations. The explanation about VFD system triggers every industrialist to run, purchase and install. In reality, the benefits are tangible. Even a lay man can understand this. Infinity Thks. Ibra - Production Supervisor.

22/07/2016, 12:17:33 AM

Operation of capacitor in the circuit??
How it will remove.a c ripples??

19/07/2016, 08:50:12 PM

What is expected life of VFD?
Is its costs worth over its useful life?

Yin (Admin):
20/07/2016, 04:39:41 PM

Hello Alind,

What is the expected life of a VFD?
If a VFD chassis is simply mounted on the wall, with no protection from dust and particulates, many manufacturers are prediction a lifespan of 5-7 years. The secret to VFD longevity is to keep it cool, clean, and free from dust, particulates, and other environmental hazards. In most instances, this is done by putting the VFD in a positive pressure ventilated cabinet with air filters. The air filters should be accessible from the outside of the cabinet and easily changeable. The filters should also be readily visible. Otherwise, the maintenance staff tends not to change them as they get dirty. We have many VFDs in cabinets of this type that have been in operation 25 years and longer.

Is a VFD worth the cost?
In most applications, a VFD will pay for itself within 1 to 3 years. Of course, this is only a general rule of thumb. In some cases VFDs can pay for themselves in only a few months. In other cases there is little or no savings. But, in the wide majority of applications, there is a significant energy savings.

Hope that answers you questions!

19/07/2016, 11:23:51 AM

Thnke you

17/07/2016, 06:50:54 AM

sir is there any vfd inverter stablizer for air conditions which i can save money on electicity and run my ac slilent with out tourq and

Yin (Admin):
18/07/2016, 10:47:56 AM


I am not quite sure what you mean by VFD stabilizer.

You cannot use a VFD on household air condition units. If you are using it with an industrial chiller, VFDs will allow you to control the speed of the motor which may in turn save electricity consumption, but it will not make your chiller run any quieter.

16/07/2016, 11:01:03 AM

very easy to understant about VFD controls and good explanations

16/07/2016, 05:08:08 AM

We want to buy VFD for our machine, to reduce the rpm of the Electric motor (10hp and 7500w)

The rpm to be 5-10 rpm. The barrel load is 800kgs and rotate for 4hrs continue.
We are based in Nigeria.
Please reply promptly
Thanks and best regards

14/07/2016, 11:23:51 AM

Thanks sir great information for beginners

mafwere muhozya mazigo:
13/07/2016, 10:42:18 AM

Very good information about VFD,Pls send me more information about VFD



Tanveer Ahmed:
13/07/2016, 02:16:02 AM

Very good information about vfds. Please keep me updated about vfds in future.

08/07/2016, 04:04:25 AM

It's really a nice explanation. thank you very much

02/07/2016, 12:22:13 PM

This session was very helpful for me.....thank you....

11/09/2016, 09:12:14 AM

can i use VFD to control the frequency of vibratory feeder?

01/07/2016, 10:18:54 AM

Got very nice explation about vfd.

27/06/2016, 01:00:29 PM

Thank you sir for providing very useful information
Thanks sir

Kabwe Edgar:
25/06/2016, 09:19:33 AM

This is a very helpful article,it has cleared some of my doubts.... thanks for sharing, continue with the same spirit of sharing and share more if you can.

14/06/2016, 07:49:25 PM

very good explanations,but i wounder kindly if you show more details in process controller related to vfd and trouble shootings

13/06/2016, 07:01:25 PM

It is more helpful for me

10/06/2016, 06:16:57 PM

good article.thanks for sharing

santosh Pagade:
05/06/2016, 10:08:40 AM

VFD is good part of electrical motor operating system ang easy to handle

rajan soni:
05/06/2016, 03:59:14 AM

Dear sir,

Please informed me why using any AC drive's ID run mode and Auto tuning running.

31/05/2016, 11:53:34 PM

how I can use VFD AC power Input 1000V ,F = 60H
I Cannot Find in the Market VFD with this input 1000V or Soft Starter for 410 KW motors.

Yin (Admin):
01/06/2016, 12:32:20 PM

Hi Yaser,

Try looking at TMEIC or Emerson. They both have 1000V VFDs.

Gurvinder Sandhu:
26/05/2016, 07:20:29 PM

Great article - I understand how a VFD works.

Naseer Muhammad:
16/05/2016, 11:45:58 AM

Very good

sisay abera:
10/05/2016, 08:31:08 AM

very good presentation

11/04/2016, 09:18:05 AM

Great article - I understand how a VFD works. I'm looking for more info on control of the VFD vs control valves. I have a central plant (hot water) feeding multiple air handlers, each has its own valve for the heating coils, current circulating pumps run full-bore with a by-pass loop for when control valves are closed. Boilers run as required to maintain loop temperature. If I upgrade to VFD pumps, can I drive the speed of the VFD (say 1-100% speed) based on the valve positions (say 10 @ 20% to 10 @ 80% open, or some combination) through my BAS system? The BAS system drives the actuating valves - I'd want to summarize their positions to create total current system demand, and drive the pump at that speed, and more or less eliminate the need for the by-pass loop. Any good articles on how to control the VFD?

Here's the key question - any good studies / white papers on the economics of this? The powers that be want to know... Technology is great and all, but without something simple to understand to put in front of decision makers, it's hard to 'sell' it without getting into the technical lingo. Nothing sucks more than trying to explain technical stuff to a non-technical crowd - *blank stare*, but talk $$$ and we can implement energy savings measures.

Yin (Admin):
13/04/2016, 09:14:06 AM

Hi Steve!

I have chatted with our VP of engineering Craig, who is in the video, and unfortunately he has not done any white papers about energy savings. He said he had been involved in two energy saving projects (one of which we wrote about, is the Industry Spotlight: Using VFDs with Reciprocating Compressors article posted on March 20, 2015) and he had done the calculations for each of the project, but he did not create any white papers since that was not his goal.

We understand all too well how difficult it is to explain the benefits of an equipment and trying to convince someone to spend a large sum of money for it. However, based on our experience we are not completely convinced that having white papers will change the minds of our customers more than having professionals like Craig here to talk to them. So as much as we would love to provide you with some more materials on energy savings, we cannot help you with it at the moment. On another note, we have created an energy saving video, have you seen it? Saving Energys Using Variable Frequency Drives

13/04/2016, 09:30:44 AM

Thanks for the response Folks!

Great quick little summary, the chart showing operating curves of damper/valve control vs VFD is a great visual to illustrate the savings. I especially liked the 107% pressure requirement for flow restricted conditions. Discussion around a <1yr pay-back on the investment really sells the case.

When you design the system, the pumps/fans have to be sized for 100% load, however in reality 100% is rarely called for. Variable speed (VFD or otherwise) simply makes sense - why run the motor at 100% all the time? Especially for HVAC, when the operating point is typically 25%-50% of total demand load for most of the season.

Interesting that this technology has been around for a couple of decades, but not widely adopted. I've heard a lot of chatter about signal interference / stray frequencies generated by VFDs, which causes all kinds of nightmares (blown motor windings, control system interference, etc.) - especially for retrofit to existing pumps/fans. Do you recommend replacing motors or just installing the VFD control module in this case? I trust the technology has come along far enough to control these hiccups. Is there design guide, or do you offer design support to engineers looking to apply this technology (like me)?

Yin (Admin):
13/04/2016, 10:10:39 AM


You are right about HVAC. HVAC and pumps are among the most common applications for VFD. Many modern VFDs also have a set point control function called PID (Proportional–Integral–Derivative) and it is very important to many HVAC and pump users.

We like to think that VFDs are pretty common these days, you will unlikely notice them outside because they are always in electrical boxes, or they are hidden in a basement corner of a building. But we also know there are many opportunities out there to expand this technology. Unfortunately VFD is not a cookie cutter type of equipment, if you will, and people may not be willing to invest the time to learn about it even though it provides a great deal of benefits in their operations.

Regarding to signal interference and stray frequencies, you might be referring to what we call harmonics. Here is a video of Craig explaining the gist of harmonic distortions . VFD Harmonics and Power Quality VFDs do produce harmonics and could potentially cause a problem to power quality. It is a real thing, so much so that we actually have a power quality expert in our company. The bigger the VFD, the more you need to pay attention to it. We think the most cost effective way to eliminate harmonics is using line reactors or harmonic filters. These additional equipment may also be part of the reason that turns people away from this technology. Here is a more lengthy article about harmonics written by Craig: Harmonics Mitigation .

Now about retrofitting existing motors, or any motors in general, we would always recommend pairing with a VFD if you need speed control. What kind of design support are you looking for specifically? Our company specializes in automation integration, from generators to motors to VFDs. I am sure we can help you with what you need. If you would like, you are always welcome to get in touch with us about your project. You can email us at bdt@emcsolutions.com, or call us at 800-800-2261, or continue to chat with us here!

25/04/2016, 01:21:36 AM

Steve forget the guessing using valve position. Use a differential pressure transmitter across mains, usually at a higher location in building as input to bas and let bas control speed. Transmitter could also be wired to vfd for feedback as most decent drives have built in pid controllers. bas is better so you can motor or log pressure.

Surbhi Hagavane:
06/04/2016, 10:23:11 PM

Thanks alot. Truely, excellent information is provided. Cleared all my doubts.

Durgaprasad shety:
31/03/2016, 09:37:34 PM

Thank you very much for giving useful information

Ramaswami Sundar:
29/03/2016, 03:17:33 AM

Dear Author,

If there is variation of input voltage to VFD will the output voltage also will fluctuate and will lead to tripping off the motor?

28/03/2016, 03:49:13 AM

good jobs but I need more information about vfd .

22/03/2016, 11:39:20 PM

What,s the work IGBT & how does it work.plz details

20/03/2016, 12:25:17 AM

I have 2kw motor.I need 3kw VFD.am I correct.

21/03/2016, 09:04:36 AM

Nazmul, you need to size your VFD based on the amps of your motor. For more details, please check out our VFD Buying Guide

Krishna V Pefnekat:
16/03/2016, 08:30:42 AM

Good information I get, but I needs more information regarding that I already fwd some messages, buy overall very good information ur giving through this media. So thanks to u n ur full team. Krishna pednekar from India presently n Egypt.

12/03/2016, 02:15:56 AM

Hi, Good technical forum,

can we fed single phase power to run 3 PH motor via VFD.

14/03/2016, 07:04:45 AM

Yes, you can provide single phase power to the VFD, which will output 3 phase power. It’s a actually a very common application for VFDs.

11/03/2016, 03:54:34 AM

dear sir please guide me . for one application I am using 3 phase 450 V 50 hz RPM 1000 motor. I want to use VFD controls for to obtain 250 rpm 500rpm . can we use vfd controls for 3phase ac motor. who is making & what is the cost?is there any limitations . lese inform
Best regards

10/03/2016, 08:59:55 PM

good morning. I have confusion in VFD rated motors. We are running our equipment with constant speed. We are exporting our equipment to different countries. Since power supply in different countries are different, each time we have to purchase the motor according to the country specified power supply. to overcome this issue, we are purchasing VFD rated motor. Will the VFD rated motor works in different countries?. To elaborate this, I am putting below example.

I am rotating a cooling drum with constant speed of 10rpm. I have used a VFD rated geared motor with 0.75kw & connected to power supply of 3ph,415v, 50Hz. Now can I use the same motor with power supply of 400v, 60Hz. there will not be any change in o/p speed (10rpm). Could you please reply.

02/03/2016, 02:56:32 PM

Could you please help me in developing energy model of the cooling unit in Simulink/matlab? Edit

I would like to develop energy model for the HVAC equipment (Energy model of the variable speed fan) and energy model of of cooling unit.

Thank you

26/02/2016, 11:17:09 AM


md akbal ashraf:
23/02/2016, 08:56:18 PM

thanx. for such a helpable article abt vfd .this made it so easy to understand ..thanks

md akbal ashraf:
23/02/2016, 08:55:06 PM

thanx. for such a helpable article abt vfd .this made it so easy to understand ..thanks

22/02/2016, 07:50:33 AM

Nice I need more details about vfd can u sent ur mail I'd to this id

antu moonjely:
19/02/2016, 10:24:48 AM

Very clear explanation.. Thanks

13/02/2016, 12:19:43 AM

Than you

s pagare:
10/02/2016, 04:04:56 AM

very nice explaination ,demonstration of VFD theory, use , benifits

Eric Watlington:
01/02/2016, 11:28:12 AM

Can a VFD work with an A/C cooling tower pump motor using differential water pressure as feedback for the frequency control? If so what equipment is needed?

01/02/2016, 03:41:42 PM


Absolutely! The vfd has I/O capabilities and PID control. It is common to use a pressure transducer to send a signal back to the vfd to control frequency. Give us a call if you have more questions.

29/01/2016, 08:01:14 AM

Good article Sir

Can we use lower HP motor with higher HP motor? I guess we can but just want to make sure.


MD Ekramul Haque:
24/01/2016, 12:34:00 PM

Very most important and I like it vfd

08/01/2016, 01:50:45 AM

Thank you so much for the article.
This made it so easy to understand.
I really needed this...!!!!

08/01/2016, 01:13:17 AM

good morning .regarding we need run 35 kw 440v 60hz fan motor but we have 380v 50HZ supply available so please give which model vfd we can use and approximatly cost. regards sivadas

01/02/2016, 02:28:08 AM

teri maa ki choot.. thankyou!

01/02/2016, 09:43:51 AM

Hello Sivadas,

Please give us a call at 1-800-800-2261 and we can talk you through your options.

03/01/2016, 05:30:58 AM

nice information

zain ul abdin:
30/12/2015, 02:30:34 AM

Is Static Frequency Driver(Converter) is also same as VFD....???

Aditi bhelawe:
27/12/2015, 06:54:39 AM

Very informative for learning

milind shinde:
23/12/2015, 12:31:47 AM

Great article!!! Thanks for sharing .i am in solar please guide me regarding solar pump

23/12/2015, 07:06:33 AM

Glad you liked it! Do you have any specific questions regarding your pump?

16/12/2015, 02:14:45 AM

thank you

Engr.Nur Mohammed:
14/12/2015, 09:22:55 AM

Thanks a lot for for your working description of VFD.I required single line diagram and part to part description.Please send me.
Thank @ regards.
Engr.Nur Mohammed.

09/12/2015, 08:00:44 PM

Is it possible to variable frequency drive a brushless dc motor without using a microcontroller? Says 60Hz give 1800rpm and 50Hz give 1500rpm of a BLDC motor.

siva rao T:
07/12/2015, 10:53:10 PM

Good.Thanks for sharing.

ritesh Chakravarti:
05/12/2015, 01:51:53 AM

Very nice content

ritesh Chakravarti:
05/12/2015, 01:51:51 AM

Very nice content

Md.kafil Uddin:
04/12/2015, 09:34:03 AM

Very nice

25/11/2015, 07:24:01 PM

i am a bit lost on VFD/rotary phase converters. would they supply constant on demand power while it is on? i've got a sewing machine with a servo motor. its MAYBE 1/4hp (the motor itself is about the size of a 12oz soda can around, slightly shorter height)

the only thing i am not sure about is if VFDs would be okay for low load frequent start/stops

this machine also has electronics/small LCD display. would a VFD be okay to use with the electronics? i really want to avoid using a rotary converter if i can because of the size/noise

Presley Chilumbu:
24/11/2015, 12:40:54 AM

Good topic on VFDs, just made my understanding. Thanx

Lisa Chen:
22/11/2015, 11:24:31 PM

Nice post. If using VFD motors, better install an insulated bearing at the non-drive end.

23/11/2015, 09:28:11 AM

Insulated bearings are a great option. You can also use shaft ground rings to protect the bearings already in place: http://www.vfds.com/shaft-grounding-rings

Often, for large power motors, we recommend a combination of both insulated bearings and shaft ground rings.

20/11/2015, 03:19:40 AM

nice yr its esey to understand thanx tu u yr thnxx

Abdul Basit:
10/11/2015, 09:05:04 PM

Please share that what will happen to the motor power and torque after the installation of VFD when it is operated at the lower frequency and rpm then its designed one. Will the torque reduce after reducing the rpm?

Abdul Basit:
10/11/2015, 09:05:03 PM

Please share that what will happen to the motor power and torque after the installation of VFD when it is operated at the lower frequency and rpm then its designed one. Will the torque reduce after reducing the rpm?

Abdul Basit:
10/11/2015, 09:05:01 PM

Please share that what will happen to the motor power and torque after the installation of VFD when it is operated at the lower frequency and rpm then its designed one. Will the torque reduce after reducing the rpm?

rajendra singh:
30/11/2015, 09:33:22 PM

how to work vfd and there connection.show me by picture.

27/10/2015, 07:42:51 AM

Great article!!! Thanks for sharing

16/10/2015, 08:21:34 PM, none

Why is the voltage to frequency (V/Hertz) important for inverters?

Is the switching time programmeable??
And why?

Thanks for any input

Appreciate your Time

Ken Salvail:
15/10/2015, 07:57:22 AM

Is it possible to utilize a VFD on a single phase system?

19/10/2015, 08:30:09 AM

Hi Ken,

If you have a single phase motor, no.

If you have a three phase motor and single phase power, yes. You can find single phase input VFDs from many manufactures. Typically they go up to 3HP. Anything above 3HP, you will have to derate the drive by getting a VFD that is twice the size (in Amps) of your motor.

If you go the route of derating the VFD, it is important to know that the VFD has to go directly to the motor and nothing else should be powered downstream by the VFD. Any lights or switches should be powered from a separate source.

Hope that makes sense. If you have other questions, feel free to send us an e-mail. Thanks.

Joe helms:
26/09/2015, 04:20:40 PM

I've noticed some inverters can be fed with single phase but output three phase. Is this true of al inverters. How does it produce the phase shift required for the third leg. Are the three legs 120 degrees apart. Unlike single phase.

28/09/2015, 04:02:35 PM

Hi Joe,

All AC Variable Frequency Drives are designed to control 3-phase motors, but not all of them will accept single phase power input. The output of the drive is not exactly a true 3-phase AC power, it is a DC generated square-wave, simulated 3-phase power.

All of the input power is inverted through diodes to create DC power so the drive is able to monitor and control the power, then the DC power is ran through IGBTs that “pulse” the DC + and – currents to create the simulated 3-phase power.

The output legs are 120 degrees apart.

AC drives are specifically designed to control 3-phase AC motors, they are not designed for any other function. For more information about how a VFD works, here is a video of our VP of engineering explaining what a VFD is: https://www.youtube.com/watch?v=wDZANW2HeJ8

Hope that helps. Let us know if you have other questions.

Tom oconnell:
25/09/2015, 11:52:30 AM

When do you know when a vfd has past it operating life . Do you have a standard to follow . A motor has a L 10 life .

01/10/2015, 09:19:22 AM

Hi Tom,

Every drive is different, but most modern drives have a 10 year expected operating life if they are kept in a cool, clean, and dry environment. Hope that helps.

mosoti D:
17/09/2015, 03:21:05 AM

thanks it is a crucial information.

12/09/2015, 11:48:21 AM

Thanks for your explanation. And I understood total theory of vfd.and we need more information about vfd

Sanket Naresh Bavkar:
31/08/2015, 10:48:16 AM

Dear Admin,

Many many thanks for this very useful information.
Your Diagrams and simple explanations has made this complicated topic very easy.
I feel like I understand all about VFDs now only :)
and I am excited to read and reply to all your blogs .

26/08/2015, 07:59:13 AM

Dear Admin,

Could you explain how a VFD really saves electrical power with the help of equations?



si bolah:
24/08/2015, 12:30:09 AM

The first time I visit your kesitus this unique and interesting I really like it

24/08/2015, 12:29:03 AM

I am very happy to read this article because of you greatly helped and thank you very much

shad md:
11/10/2015, 08:07:53 PM

I am very happy to information

Mas bram:
24/08/2015, 12:27:43 AM

thanks for sharing dude, I was greatly assisted by the article from you this

24/08/2015, 12:25:34 AM

wow this is information very important

15/08/2015, 10:57:04 AM

Hi, thanks for nice site. Does the output of the inverter 200 V to 12 V, 12 V, 50 Hz with reduced and motor launches. Thank you. - See more at: http://www.vfds.com/blog/switching-it-up-igbt#sthash.3koTVK4B.dpuf

11/08/2015, 03:19:11 AM

How the VFDs handle the power factor correction and the reavtive power?

09/08/2015, 08:16:55 AM

That was good information regarding VFD, VFD itself the answer of speed control.My question is if my Process Reactor's RPM is set with 68 max.so is it possible with the help of VFD i can make my RPM more than 68? if no that mean VFD means always decrease the RPM not increase...am i right?

abhas singh:
07/08/2015, 07:27:03 AM

sir, by which mechanism the voltage is reduced in vfds

07/08/2015, 04:00:44 AM

sir plz tell me how much % of total current take v.f.d. in starting.

06/08/2015, 05:30:39 PM

What is the typical efficiency range of a VFD controller? How many watts of power are drawn for the energy consumption compared to the watts of electricity passed through to the motor?

I presume this is impacted by the size of the load (motor), but am interested in a range of efficiency at the range of controlled output speeds.

Any suggestions on where I might find some information on the controllers?



03/08/2015, 08:50:22 PM

In india some wind mill generator available at 3ph 80 volt, 120 volt series. what kind of load used for this voltage? Normally in india ac is 3ph 440volt.

31/07/2015, 02:47:40 AM

What is minimum frequency of vfd that my motor will start to rotat.

bharat jadav:
31/07/2015, 02:20:12 AM

Thanks for your guidance....

bharat jadav:
31/07/2015, 02:19:04 AM

Thans for your guidance.....

sivaraj palanichamy:
28/06/2015, 09:30:35 AM

Sir actually i want to run 415v 5hp motor with this drive, so what the capacitance value i want to use for dc bus?

Prabhakar v patil:
06/06/2015, 02:49:26 AM

Good diagram & spcificatio

20/05/2015, 07:52:09 PM

Please let me know with so many electronic components in series.What is the overall reliability of VFD
RS Yadav

13/07/2015, 10:03:00 AM

If you size the VFD properly, keep it cool, dry, and clean; they should run for years. In our experience, we have heard them last between 5-25 years.

sivaraj palanichamy:
04/05/2015, 11:39:11 PM

Dear admin, actually in my area only 3hours will be 3 phase current available, the remaining timetime will be 2phase current only, in this situation can i use VFD for my submersible water pumb on 2phase current?

Azeez Monsur:
14/07/2015, 11:22:35 AM

I doubt if this can work, as some VFDs experience undervoltage when required phase is not complete. You need a complete 3-phase input to avoid the devise from being tripping off.

Nishant Shah:
01/05/2015, 12:38:42 AM

If we have VFD does there is need of Stabilizers or Voltage Controller equipment to protect our motors, VFD's if Yes why, if no why ?/ please explain.

13/07/2015, 10:06:00 AM

No Nishant, you do not need them to protect your motor. However, you might need line reactors to reduce the harmonic distortion.

Azeez Monsur:
14/07/2015, 11:24:23 AM

You don't really need any protection appliances once you are using a VDF, it comes with many protection funtionalities.

29/04/2015, 06:00:44 PM

I'm running 5.5 kw motor coupled to 7.5kw inverter. The motor draws 10.7 amp when 400v and 50hz when running with inverter its frequency will drop to 28hz and how much the vo lol tage and current would be at this time will burn my motor.

13/07/2015, 10:11:00 AM


We need a little bit more information. Did you set the parameter for speed to 50 Hz maximum? Does it ramp up to 28 Hz and stop?

Raj kumar singh:
24/04/2015, 10:33:04 PM

Does vfd reduce starting current.If yes than how much in percentage.

26/04/2015, 10:12:03 PM

Yes it does. A VFD virtually eliminates "inrush current".

22/04/2015, 07:58:09 PM, VFDs.com

Thanks For the Information.

Tim G:
18/04/2015, 09:33:47 AM

I really over spec'd a ventilation fan/motor. 30 HP 460V. Should have been 20 HP. Does the VFD have to be rated for the existing motor or the speed/draw I want to operate at?
My guess is the VFD has to be 30 HP.


13/07/2015, 09:06:00 AM

Tim, you are correct. You have to size the VFD based on the motor's spec. More specifically, you have to find a VFD that has a higher or equal amp rating than the motor.

sheetal :
16/04/2015, 07:15:52 AM

which power vfd can display on panel ? induction motor input power or shaft power?

Navneet Gill:
06/04/2015, 01:56:03 AM, www.yogijidigi.in

Thanks For the Information, It is very useful for us specially schematic diagrams helped a lot.

06/04/2015, 09:22:00 AM

You are welcome Navneet, we are glad that you found the article useful.


Pardeep :
04/04/2015, 07:26:21 AM

I have Schneider altivar avt312 ac drive
My motor running load is 15 amp
I want to get load under 12 by ac drive
Is it possible
With changing frequency

07/04/2015, 09:48:00 AM

Hi Pardeep,

What application/machine are you with your motor?
What do you mean exactly when you say "running load"?
What exactly are you trying to do?


Roberto Perez:
06/03/2015, 12:58:00 PM

How much can we load a VFD for ESP's (electro submersible pumps) applications? Its true if we under load a VFD do we have more chance to get harmonics than if we load it properly ( let's say 80-90% )

11/03/2015, 02:47:00 PM

Hello Roberto,

Sorry for the delayed response. We consulted our field engineer about your questions. The lighter you load a VFD, the higher the harmonic distortion will be. If you stay within about 15% of the full current of the VFD, it should be fine.

We are unsure what you mean exactly when you "load the VFD". If you are asking how close can you get for sizing, then it is typically within 5%; possibly closer if the pump is only moving water. Technically, you can use the full range up to the rated current rating. However, we generally like to be conservative and not be right at the top of the range of the VFD rating.

If you are asking about overload conditions, the drive will run to the preset overload values that are in the drive as it relates to the parameter set points (i.e. 110% for 60 seconds at SLD rating of hte FLA in parameter #9 [Mitsubishi], or 150% for 60 seconds at LD rating of the FLA)

Let us know if you have more questions! Thanks Roberto.


rana noman:
04/03/2015, 06:53:54 AM

can v use single phase phase motor with single phase vfd? in other words i m going to make my course project i m going to make a prototype of my idea and in this idea i m going to design a vfd motor and initially i m going to use very low power motor with vfd

Yaseen Subahani:
05/03/2015, 09:49:07 PM

Yes u can use single phase motor with single phase vfd. And I already done this project.

11/03/2015, 02:50:00 PM

Theoretically, yes you should use a single phase vfd for your single phase motor. However, single phase VFDs are not very common. We haven't heard of that many in the market.

26/02/2015, 10:32:09 AM

Does it make a difference between 480Y or 480-Delta, corner ground, services with regard to input wiring?

02/03/2015, 11:16:00 AM

Hi Mike,

No, it makes no difference for a VFD whether you have 480Y or 480-Delta input. Most incoming services are 480Y. Hope this helps!


22/02/2015, 11:16:46 PM

Is it possible to use 3 phase variable frequency drive for 1 phase motor to differentiate the speed of the motor?
Please give me your advice

23/02/2015, 10:02:00 AM

Thanks for the question Raj. No, it is not possible to use a 3 phase VFD to power a single phase motor.

Bakare Kehinde:
21/01/2015, 05:49:32 AM

How does the VFD work in varying the frequency and voltage supplied to the electric motor.

21/01/2015, 10:45:00 AM


The VFD is able to vary the frequency and voltage through the use of IGBTs. It is through the fast switching of IGBTs, which creates PWM wave, that allows the VFD to alter the frequency and voltage supplied to the motor. You can read more about IGBTs in another post on our blog here at:http://www.vfds.com/blog/switching-it-up-igbt.


03/01/2015, 05:35:59 AM

what type of motors can be used with vfd?

09/01/2015, 04:25:00 PM

For the VFDs available on our site you would need to use a three phase motor. Please let us know if you have any more questions about finding the right VFD for your motor.


silviu dima:
27/12/2014, 10:01:19 AM

How should we choose an appropriate VFD ? Let's say we have a X KW motor, what kind of VFD shall we consider ? I mean, the maximum and minimum limits in KW.

29/12/2014, 07:42:00 AM


When sizing a VFD to a motor you want to match the FLA listed on the motor nameplate to the amp rating on the VFD. You will need to consider what application you have because this will determine what overload rating you will need on the VFD. Take a look at our VFD buying guide here:


This article will help you better understand everything that needs to be considered when sizing a VFD.

24/12/2014, 11:47:19 AM

pls. advise if any motor operate with fixed speed for example (1500rpm, 50HZ) CAN OPERATE WITH VSD ?

22/12/2014, 12:31:00 AM

This is really informative material which you shared with us. Thank you very much... Can you help me out with this, I were working on micromaster 440, it gives fault indicates overcurrent error. I unplugged the motor termination, on the drive but still found the same error. I know the drive is faulty but I am interesting to know what were the reason.. Is it the transistor malfunction or capacitor or any other? I will be very thankful if you upload some troubleshooting case studies related with VFD repairing.

Service engineer

22/12/2014, 12:45:35 AM

I would be very thankful if you clarify me in below contents
I found at motor input from drive, we occasionally placed chock transformer. I heard the purpose of it is motor protection, but how it protects if AC square wave is appropriate for motor operation as you told in article..

Thanks in advance

22/12/2014, 12:38:00 PM

It is really hard to say the exact reason for your overcurrent error without being able to directly take a look at the drive. There could be several reasons why you are having problems. Our recommendation would be to take it somewhere for diagnostics. If your location is close enough to us, you could send the drive in to us fpr diagnostics to address the issue. If you would like to do that, we can send you a repair quote.

As for your other question about DC chokes. A choke reactor is usually used on a dc bus of a drive to help with harmonics that goes back on the line.A Dv/dt filter or sine filter will help with the square wave form, which you mentioned. If the motor is not too far away from the drive it isn’t too much of a concern if you don't have one, but if it is 100 ft from the drive you should take a look at using one.

Bryan Charlton:
17/12/2014, 07:48:53 AM

Why would the switchgear that is feeding the VFD show a different current reading to that showing on the VFD?

17/12/2014, 08:43:00 AM

Without knowing more about your application it is hard to give a definitive answer. But, typically they will be different because the VFD and switchgear are not calibrated the same. The amperage that you will see from your switchgear will include everything that is on the switchgear while the amperage from the VFD is just from the motor.

Bryan Charlton:
17/12/2014, 08:49:06 AM

Sorry that was a bit misleading by me the current reading on the MV switchgear is of the CB feeding the VFD so it is dedicated to this application only.

Bryan Charlton:
17/12/2014, 09:08:16 AM

I should add also that the VFD is reading less than the switchgear up until the rated frequency which then they are identical.

15/12/2014, 09:29:10 AM

What would cause a DC overvoltage message on an AB 300HP VFD?

16/12/2014, 08:27:00 AM

There are several reasons that might cause a DC over voltage. It is hard to identify the reason for this with out knowing more about the application. If you would like to call in and talk with one of our engineers at 800-800-2261 we can help you figure out what is causing your over voltage.

05/12/2014, 08:48:35 AM

Can I use your definition in a publication?

Asmat ullah khan:
28/11/2014, 04:08:29 AM

what would be the minimum DC voltage from DC voltage source on DC bus of VFD to run the induction motor?

03/12/2014, 09:27:00 AM

The DC bus voltage is directly related to the supply voltage. There is a DC bus voltage at which the VFD will trip on under-voltage and will not run at all. This will vary depending on the drive manufacturer. For one brand of drive that we offer, the DC bus under-voltage trip is set at 430V for a 480V drive. The typical DC bus voltage for a 480V drive is about 650V. Technically speaking, there is no absolute minimum voltage that the DC bus will function at, but rather a minimum source voltage that the VFD will consider acceptable voltage to operate safely.

25/10/2014, 02:50:39 AM

Does vsd help for heavy load start

11/11/2014, 04:42:00 PM

Yes, it does. Base on the overload rating of the VFD, it can give you full load torque and more at all speeds, including dead stop without the typical high current associated with across the line motor start.

Ralf Meister:
16/10/2014, 07:03:02 AM

I have seen VFDs offered with 120V single phase input and 230V output. How can you get 230V out of 120V without a transformer?

Jon Novak:
22/10/2014, 11:55:35 PM

240V output is no more than 2x 120V lines phased @ 180degrees. Likewise 208V 3phase is 3x 120V lines phased at 0, 120, and 240 degrees. If you are handy with how you capture the AC power and convert it to DC, you can get a + and - DC rail at the cost of needing more current. Which will allow you to use the VFD portion to phase the output and get you the phasing you need to get "2 phase" 240, or 3 phase 208.

FYI in your house, this is exactly how its done. You generally get a neutral and 2 hot legs legs of power each having 120V (to neutral). But hooking Hot/Hot will give you 240, since they will be 180 out of phase.

Jun Pascasio:
29/01/2015, 10:38:41 PM

A device called Joule thief can do that. It is a configuration of a capacitor and an inductor. The configuration causes a build-up of charge at the output terminals. The oscillations on the R-C circuit makes it possible.

08/10/2014, 02:48:28 AM

What is the relation between speed and power consumed by VFD

08/10/2014, 04:40:00 PM

HP = (Torque(ft-lb) * Speed(RPM)) / 5252
KW = HP * 0.7457

The above equation shows us that there is a third element outside of speed and power that must be taken into account. Torque is determined by the load. Essentially while there are small losses in power in the VFD and the motor (both are extremely efficient) you will not be able to determine the consumption of power without knowing the torque.

12/10/2014, 02:14:11 AM

what must be the rpm value, full or sync rpm?

28/08/2014, 08:59:51 AM

What controls are out there to determine the output frequency in order to match the load? In an heat pump application is this controlled by temp sensors and programmed logic similar to a traditional technology?

25/08/2014, 02:22:10 PM

I've been told to purchase an inverter for a pump application. Is there a difference between an inverter and a VFD?

12/08/2014, 01:23:56 PM

Is it possible to use 2-wire hard contact to remotely vary the speed of the motor between 50% and full speed when using your VSD device.


Engineer Samson rotimi Oladipo

12/08/2014, 06:17:00 PM

Yes, the drives include preset speed inputs. The two wire contact would be wired to the preset digital inputs.

01/09/2014, 04:51:13 PM

Thanks for the answer, the actual thing we want to achieve is, if the two-wire hard contact are bridged we want to have 100% full speed and if the wires are disconnected, the motor should be running at 50% speed. Is it possible ? and how can we achieve this with the preset digital inputs. Could you help us with a typical sketch or diagram or drawings.

Thanks for using your time to help out.

Engineer Samson Oladipo

04/08/2014, 06:39:22 PM

I feel am already expect in VFD's. This presentation was clearly explained from what is to why we use it.


31/07/2014, 08:37:14 AM

Thank you for the great information on VFDs.
When you reduce the voltage to maintain the magnetic flux ratio (V/Hz), what happens to the current?

31/07/2014, 11:32:00 AM

If the motor is running, the current will be roughly proportional to the torque required by the load.

31/07/2014, 12:56:13 PM

Forgive me if I am being obtuse; I'm new to this. If you reduce the frequency from 60 to 30 Hz and maintain the same load, what will the current do?

08/08/2014, 03:43:00 PM

If the V/Hz is constant, the Amps will be roughly proportional to torque, regardless of speed.

Ikhtekharul Islam:
13/07/2014, 12:59:11 AM


Myo Kyaw:
11/07/2014, 06:11:48 AM

Thank you very much for very useful information. I wish I could also read how switching with transistors is done to achieve required frequency and about frequency modulation.

15/08/2014, 02:57:00 PM

Thank you for your comment and the idea for additional content. We have written an article about the switching of the transistors. Here is a link to it:


15/08/2014, 02:57:00 PM

Thank you for your comment and the idea for additional content. We have written an article about the switching of the transistors. Here is a link to it:


09/07/2014, 01:11:40 AM

Very very good information

01/07/2014, 09:17:18 AM

In the V/Hz discussion I can't find the reference "(see the VFD Motor Theory presentation for more on this)" . Where is it located?

This site is a great, informative discussion of VFDs.

01/07/2014, 04:56:00 PM

Thanks for the kind words and for your question! We are currently in the process of editing the motor theory post but I think I can help answer your question about the V/Hz ratio.

Motors are driven by magnetic poles. The strength of the magnet is proportional to the ratio of the voltage divided by the frequency (V/Hz). If the ratio is too low, the motor will be too weak to provide full torque on the motor shaft. On the other hand, if the ratio is too high, the iron in the motor will saturate because it is being pushed too hard. It will overheat and start to smoke, and eventually fail. Therefore the ratio must remain constant.

To illustrate this further, at 460V and 60Hz, the magnetic flux ratio (V/Hz) is 460V/60Hz = 7.66 V/Hz.

Now it’s important to remember that this V/Hz ratio must be maintained in the VFD. When you reduce the frequency you must also reduce the voltage. If you were to reduce the frequency, say to 30Hz, the new required voltage to maintain the ratio would be approximately 230V.

V/Hz Equation:
Magnetic Flux = V/Hz
Example: New Voltage (230V)/30Hz = 7.66 V/Hz

I hope that answers your question. If you have other specific questions, let us know and we would be happy to answer them for you John.

01/07/2014, 04:03:09 AM

thank u .... super tutorial guys

29/06/2014, 10:33:04 PM


29/06/2014, 08:09:43 PM

it is a interesting subject.attach more of the same

26/06/2014, 02:07:59 AM

here good and knowledgeable information about vfd.

amancio tapasao jr:
09/08/2015, 09:55:20 AM

Even big motor its ok using vfd?

jonah mutua:
04/01/2018, 04:55:04 AM

An alarm "converter failure " pops on dispay panel and trials to clear it have failed. The drive is siemens mm440. please help.