How to Size a VFD for 3 Phase Motors

Are you looking to match a VFD to a motor? Join Keith from eMotors as he guides us through the ins and outs of selecting the right size VFD for a 3 phase motor. You'll learn about how to read the motor nameplate, matching Full Load Amps (FLA), Constant and Variable torque VFDs, voltage, RPM, and different applications and enclosure types.

0:00 Introduction
0:28 VFD Sizing Intro
1:15 Matching Full Load Amps (FLA)
2:00 When to Oversize the VFD
2:13 Voltage, RPM, & Speeds
2:59 Modern VFD-Rated Motors
3:30 Different Applications
4:57 Altitude Effects
5:38 Environmental Temperature
6:10 Conclusion

[garbo]

Another important thing to consider when purchasing a VFD. Purchase quality line reactor & if critical loads go with the bypass feature that has three contactors. M1 powers drive in put M2 is on output side & M3 when closed urs interlocked so M1 & M2 contactors remain open. Had some bypass VFD'S have a test position on hand, off, auto selector switch that I never done it but you can troubleshoot drive while motor is running full speed thru the M3 bypass contactor and believe it allows M1 input contactors to supply power to drive.

[garbo]

We had over 500 VFD'S from where I retired from 2 to 1, 750 HP. The extremely knowledgeable salesman that I ordered replacement or a drive for a new location he always told me that drives are rating in power ( KW ) & not horsepower. Of course every VFD he sold us had a horsepower rating along with ampere. Would send him a picture of the think it was a combination of 26 letters & #'s from serial # on old drive and he cross referenced that also. On a few critical pieces of equipment we ordered the next size HP. For a 40 HP motor would order a 50 HP drive and a 60 HP motor would order a 75 HP drive. Would downsize input fuses and adjust trip Amps on overload block.

[tomglenn]

This for me was a timely piece....'sizing'... I've looking for reasons for a overheating issue with the ( a supposedly 150% 'appropriatley' rated chineese generic) VFD .
My project is a current Commercial Front loader Washer but with 'cooked' control electronics: but everything else in good seviceable order for the decade or more. Mind you; 'she's no longer what could be strictly described as automatic.
Happy now to put down a few hundred bucks on a nameplated VFD unit..
Big thumbs up.

[HamidShazin]

Hi, thanks for the useful information. I'm having a speed issue on a 3 phase asynchronous motor with specs as 4kw/1435 rpm/ 380v. Upon startup it rises to 15+ bar pressure which is too high for a petrol line. Would a VFD (5.5kw) solve the issue of controlling the speed on it?

[looseslacks]

Hi keith, awesome video. I'd like to know if a vfd is suitable for my 3phase, 4kw, 2900rpm reciprocating compressor? I think I should use a soft starter but those are hard to find where am at. Main reason for the installation is to reduce the starting amps draw of the motor as it will be connected to (3) 10kw inverters with a 15kw lithium battery. Nnoruka from Enugu, Nigeria

I also have a 7.5kw - 11kw inverter I'll like to install on a 3phase, 11kw, 1400rpm reciprocating compressor if the first installation works out fine. Altitude and temperature are within spec. Waiting for your experienced insight. Thank you

[dennisleazott]

I would like to add a big red STOP mag-switch with a VFD I'm installing on a old rockwell delta bandsaw (1.5hp). I could put the switch between the source and VFD or VFD and motor. Any recommendation for placement?
Thanks,
Dennis

[robertwalton]

Say you double the rpm of the motor by doubling the frequency, does that also double the motor's power output?
Would you need a VFD with twice the power rating?

[bushratbeachbum]

I've got a bandsaw with a CMG 3Phase 380-420v 3.3kw 4.5A 1430rpm motor on it.
Can you recommend a drive to run it on single phase 230v please?
Could you mention the potential current draw on the single phase supply also?
Many thanks!
Great video!!

[fuzzfacelogic]

Thanks very helpful. I'm using a 55 year old 3ph 2 speed 1.5hp Swiss made EMB motor and it works very well but I only have a single phase supply. So I connected up a 2kW VFD and it is working okay apart from not enough low speed torque. Is there a way to correct for this?

[mustehsankarim]

I want to run 5hp centrifugal pump 3phase on single phase supply which vfd will be suitable is 5.5kw vfd is enough?

[nileshkharde]

Kindly guide for crane application which VFD should be used

[sanjaykumarsharma]

Great video. However I have one observation about the statement that VFD Horse Power( say Power Rating) shall match with motor Horse Power. In my understanding motor rating means shaft power out put which will require bigger electrical input depening upon the efficiency of motor. Further there will be electrical power loss( I2R loss) in the connecting cable between VFD and the motor terminal, whatever small percentage it may be. So in my opinion, VFD output shall not only be able to meet shaft power, but also total power loss in motor plus cable loss. Kindly correct me if you feel otherwise.

[rilindmushica]

I have a 3 kW Cavity pump in my factory that is driven by a VFD Drive. The datas of my VFD are (3 kW CT, 4 kW VT). Now, I want to change the 3 kW pump with one that is 4 kW, should I change the drive also? As a Note, my pump should carry the pressure of oil almost constant.

[apolinariomercado]

Hi Sir, can i use vfd to a press drill machine with the name plate of 3 phase induction motor, 4pole, 1.5hp, 60hz, 440volts, 2.75ampere, 1700rpm, ins F, amb 40degC, cont.rating. Thanks in advance, Paul Mercado

[ahmadsaaty]

Hello, I would like to know what size should the vfd be if I have an urban lift motor rpm 1385, cv.:5.5, volt: 220/380, Amp: 23/13.3 as shown on the motor plate. also what is the recommended electrical installation that should be used as protection for both the vfd and the motor? thanks

[PeterHatch-mxzc]

Have 1.5 hp 3phase rpm 3450 what VFD do I need or will it work thks

[firetoy]

can the vfd be far away from the motor it serves?

[SpringCleaningLOC]

Are most VFD's capable of converting single phase to three phase? It looks like you just use L1 and L3 as the input, then oversize the VFD, is that correct?

[kingsize]

I want to use VFD for three phase 10 HP water pump on single phase electricity

[GHohn]

A compressor is not constant torque. The torque will vary with the pressure head the pump must overcome.