Multiple hp motors on same vfd?

[PT Doc]

I have a kb vfd for a 3hp grinder. If I wanted to add another motor, for say a disk grinder, could I add a 1hp motor? I remember there was a toggle I side the unit to picks the hp that it was running.

Thanks for the help.

 

[DAMNENG]

Depending on the make of the VFD, generally you can specify in the setup what HP is for the motor you are controlling. The VFD then limits the maximum current draw to what is typical of that HP motor. You can drive a smaller motor with the drive but it won't limit the current unless you change the setup.

You can put a multiple pole switch on the output of the drive to select which motor is being driven. Make sure you don't switch between motors without securing the power to the first. You night fry the VFD or yourself if you aren't careful.

Jim Arbuckle
ABS JS

 

[timgunn1962]

I have a cheap Chinese 3 HP VFD mounted in a dust-proof box with a 3-phase power socket and a remote control box on a trailing lead. Any of machines in my "shop" can run off the box with the remote control moved to the machine in use.

It runs everything from a 1/2 HP blower, through a 1 1/2 HP lathe to a 3HP work-in-progress grinder. As Jim says, there's effectively no overcurrent protection from the drive itself when running a small motor on the big motor settings. It doesn't bother me much, as the protection is an "extra" and would not be there if I was plugging the machine directly into a mains 3-phase switched-socket.

It's no problem with V/F drives, but if you have a Sensorless Vector drive, it's unlikely that the rating plate power factors of the different motors will be the same. I don't know how much of a problem, if any, this will cause, but SV drives have some fancy electronics inside to tweak the voltage and maintain the programmed power factor. V/F drives "just" increase Voltage and Frequency in a fixed ratio.

Tim