New question about VFDs

dr sportster · Jun 26, 2015

If the single phase motor is 1/2 hp how do you rate the VFD size. The VFD is not much more money than the static converter. So can it be for more HP or does it have to be an exact match.

Steve@Advance · Jun 26, 2015

The VFD provides overload protection for the motor, so it needs to match.

1/2 HP sounds small for a lathe, sure you read the tag correctly? Also might double check that the motor is wired for 220v, not 480v. Simple to change if it's a 9 lead motor.

Sparktrician · Jun 26, 2015

Within reason, it can be oversized. The vid does provide overload protection, but that is one of several parameters you program into the drive

buickanddeere · Jun 26, 2015

I think you are asking if a 1/2 HP three motor is supplied through a VFD from single phase. What should the VFD rating be ? Absolute minimum capacity margin is 1.73 times larger and 2 times larger is better.
A 1HP drive can be programmed to protect and operate the 1/2 HP motor.

David G · Jun 26, 2015

That is not correct.

There are 2 parts to a VFD, the first part charges a DC Bus, the second part provides the 3 phase output. The VFD should be sized at least 1.73 times the KW of the 3 phase motor so that the DC bus can get charged from the single phase input power. You can set the output FLA and service factor whatever you need for the motor, if it does not exceed the VFD capacity.

dr sportster · Jun 27, 2015

Thanks to everyone who responded. I think Im going to go with the VFD as the idea of the static converter seems obsolete.

Tramway Guy · Jun 28, 2015

When using a 3-phase VFD with only 1-phase input, the power throughput is limited by the input section. That's why you need to oversize the drive.
As others have stated, you program the drive to match the motor nameplate. You might also have to set a parameter to ignore a phase failure fault as well.

Hogleg · Jun 29, 2015

I did this on my Craftsman lathe around 10 years ago. Used a Baldor 1/2 hp, 3 phase motor ( bought NOS on ebay for $50) and a used Alan Bradley VFD from ebay. The low HP ones go for pretty cheap so I bought 2, one to use and one for spare. Bought from a dealer that guaranteed not DOA. Got the programming info from a google search.

Net - worked perfect. Could set startup and shutdown parameters. Also could vary frequency to get 2:1 speed control without having to change belts. Had to be the best modification I ever did to that old lathe.

I did have to change the pulley sizes because the motor had a different RPM than the original. The lathe had a jackshaft so was easy to do.

Read the instruction manual on proper sizing. Download it first. I recall I used a 3/4hp VFD on that motor and had no problems with it.

John

New question about VFDs

dr sportster

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Steve@Advance

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Sparktrician

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buickanddeere

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David G

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dr sportster

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Tramway Guy

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Hogleg

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