i have a question about variable frequency drives.can one unit run more than more than one motor of the same horsepower & voltage?the reason i ask is we have a machine that turns spindles for buffing stainless steel. we use a 40:1 ratio gearbox now , but that is still too fast.this machine has 12 spindles. i belive each motor is 3hp 3 phase 440 volts 1725 rpm.if a VFD can control more than one, how many max?THANKS for any replies!

I am no expert on vfd's.You usually install one for each motor.But I have also not installed them on such small motors.I would think a cheaper type of speed control would be better.I do not see why you could'nt supply two motors with one.Just my two cents I guess.

You can. But you will have to add motor protection for each motor, whereas with just one motor the vfd usually will do that job also.

wolfgang,would you add up the total horsepower of all the motors & buy that size unit or would the single motor size work?the example would be 3hp X 12 for a total of 36 hp.surfinsparky, what kind of speed control could be mounted in a starter cabinet? all 12 of these motors run at once.

I have never tried multiple motors on one VFD....and I'm not sure I'd want to!
Regardless of the nominal RPM of a motor, every motor is going to run a little bit different. Likewise, the load applied to each motor is going to vary slightly.
Invariably, production lines have some means to adjust the line between stages, to account for these factors. Yet, I still would not count on every motor running at the same speed. I'd really like there to be separate VFD's.

circuit man, I have seen it done but all the motors were working on the same load. We had a large diameter pipe puller with eight tractors each with its own motor. I am not sure that it would be a good idea if all the motors were not under the same load. If your loads are close enough together it might be better to link your gearboxes with driveshafts and run only one motor.

VFDs supply current. Simply add up all of the motor currents (do not use HP) and purchase a single drive of at least that size. Check with the VFD manufacturer, it would be normal for them to require some type of load reactor/filter (maybe even one per motor).

Also each motor will require it's own overload protection.

All motors need to start at the same time, do not have the VFD "at speed" and then turn on motors. This is called "slamming" and requires more complicated sizing.

Have you tried smaller diameter mops?

hi guys! thanks for all the info.we can't use a single motor because it's a revolving table.the motors all start at once.there connected by a collector ring.what's a mop?

circuit man. I imagined, from your description, a machine using 'mops' or rag-wheels to polish stainless-steel components. Reducing the 'mop' diameter reduces the peripheral speed.

Alan