Re: [CAD_CAM_EDM_DRO] VFD's, running a larger motor than the rating....

dougrasmussen@... wrote:

> Group,
>
> Maybe someone knows the answer....
>
> Are there any bad effects of running a larger motor than a VFD is
> rated for? For instance, if I had a 5hp motor and only had a VFD
> rated at 3hp. I would set the VFD's max amps output at the
> approximate setting for a 3hp motor, so the 5hp motor would never be
> running at it's nameplate current rating. Would I get the equivalent
> output of a 3hp motor from the 5hp?

Yes, there could be problems. The larger motor has lower resistance and

inductance than the smaller one. The difference between 3 Hp and 5 Hp
is
small enough that it is not likely to cause a problem. but, I blew up a
1/2 Hp
VFD with a 1 Hp motor, due to this problem.

Also, when running a motor designed for higher frequency with a VFD
designed
for lower (60 Hz) the same problem comes up, only worse. I had to add
series
inductors in the motor leads to get the high freq. motor to work.

Yes, you should get the full 3 Hp out of your 5 Hp motor, assuming there
are
no problems with the lower inductance.

> This seems like an easy question, but every motor guy I've asked
> doesn't know the answer (or tries to sell me a bigger VFD).

I got this info from talking to the people who design the inverters at
Magnetek.
I needed to run a 400 Hz motor, and their inverter DOES go all the way
to 400
Hz.

Jon