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

There are two main types of AC motor speed controllers. The
VFD type supplies full current at different frequencies. The
SCR type runs at line frequency and chops the power
effectively controlling the current. So if you current limit
the VFD it looks to me like you would be in effect combining
the two systems. I don't think the motor would work very
well because it needs its maximum current to start and then
uses less current when it gets to speed.
Darrell

----- Original Message -----
From: <dougrasmussen@...>
To: <CAD_CAM_EDM_DRO@egroups.com>
Sent: Friday, September 29, 2000 3:47 AM
Subject: [CAD_CAM_EDM_DRO] VFD's, running a larger motor
than the rating....


> 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?
>
> 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).
>
> thanks,
>
> Doug
>
>
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