Rpc idler motor question

A while back I built an rpc and it has been great. My question is can I use the idler motor to run a piece of equipment?

I built a 2x72 belt grinder a couple years ago and love using it but it tends to bog down easily doing heavy grinding. It currently has single phase 120v 1hp motor on it. I thought about finding a small 3 phase motor to power it thinking it wouldn't bog so easy being three phase which led me to thinking just to use the rpc idler to power it. So here I am asking if it can be done or not.

My idler is a 5hp unit and sits on the floor so I thought just putting a pully on it and getting a longer belt would work just fine. But I'm not sure if the 3 phase idler only running on single phase power could carry a load.

You can, with limits.

Input power gets used to produce power.... That can be generated electrical power, or it can be shaft power. The motor has a limited amount of power available, AND as an RPC, there are some more limits, like the allowable voltage drop, etc.

Use up some of the available power as shaft power, and that leaves less for RPC uses. And, because it slows the motor, it drops the output voltage also.

So, basically, yes you can, but it is best when the idler is used as a motor only when there is not any 3 phase RPC output power needed. Grinders might be doubtful only because it depends how much you like having a large "synthetic stone" spinning unused and unwatched in the shop.

As JST says. If you use the idler strictly on the grinder, you will get about 70% of rated power single phase. It would be less than that without capacitors. If you only use one machine at a time, it would work well. But don't try using belt sander at the same time as another machine. You will overload the idler motor. You should also have a clutch between the belt sander and the idler.

Tom

Ah... Saw "grinder", missed "belt". So no synthetic stone.... just two rollers and a belt, maybe

Yeah, a clutch would be good. Saves belt wear, and makes less noise, at least.

Just spinning things without a load is not generally a problem for the output power, but using it hard and also wanting power to something else might not work well.

And, even though the idler is a 3 phase motor, it IS running on single phase, just GENERATING on the 3rd wire... So you'd only have about 2 HP at best vs the 1 HP you have now.

Thanks for the info guys. I only ever use one three phase machine at a time anyhow on the rpc. Maybe I'll just look for a 2hp single phase motor. Sounds like it would work the same and be a whole lot smaller. I just thought maybe the three phase motor would have more power but now I known running on single phase it really wouldn't.