Primitive RPC question

This may be a silly question, it certainly shows my lack of savey on rpc's but here goes.

I plan on building a poor mans rpc, 3ph motor started with a 110V pony motor.

I know the "idler" should operate without a shaft load but I'd like to direct couple the pony and the idler to make setting up a remote start panel less of a headache.

Would spinning a powered off 110V motor constitute too much load?

I didn't notice any references to this question on other threads so if it's common or has been asked before my apologies.

Any help or info is appreciated, my static convertor just gave me the ominous white smoke.

David

Most people decouple the pony motor from the idler.

If you remove power from the idler so that it is being spun by the idler, I bet it would be fine as long as your idler is decent sized and your pony motor is small.

-Joe

"Would spinning a powered off 110V motor constitute too much load?

"I didn't notice any references to this question on other threads so if it's common or has been asked before my apologies."

This could be called a belted idler.

In theory, you can belt a pony to an idler to an idler, but a pony to a single idler is best.

For lowest starting current, the idler should be rotating at synchronous speed, not rated speed, when it is first placed across the line.

For a four-pole idler, the rated rpm is usually 1725, whereas the synchronous speed is 1800 (60 Hz case, of course).

This would require a 1725:1800 = 1:1.043 step-up.

But, 1:1 is usually good enough.

If the pony is small enough, yet large enough to reliably start the idler under all conditions, and the pony, at least, has permanently lubricated bearings, it is pretty safe to belt-connect the two.

Thanks guys, I know the belted idler is a common design I just know most decouple after the start as you mentioned 2Slow.

I'd been considering a shaft to shaft direct drive like a Lovejoy to make things just ridiculously simple, but if it could be reliably done this way why wasn't I hearing of anyone else doing it?

Idler load I was worried about, alittle wear on a permanently lubed pony not so much.

I'd like to put it in an enclosure and hide it away behind a mill to save floorspace and set up a remote start panel, hence the difficulty decoupling.

This is kinda a quick fix since my static died, later I'll probably add run caps and maybe replace the pony with start caps when and if I can wrap my electronically challenged mind around the how to paticulars.

Thanks again for the advice guys, any other input is certainly welcome too.

David

I seem to recall one poster here in the past that had a problem with a direct-coupled
pony motor which caused a considerable load on the idler motor. Not large enough
to bog it down, but large enough such that a considerable amount of heat was
dissipated in the pony motor, in spite of it being de-energized and disconnected.

It was a pretty subtle issue involving the motor acting, I think, as a self-excited
generator and there were currents flowing in places one might not expect.

I seem to recall it may have been an unusual type of motor, maybe capacitor
run or something. Does this description ring a bell with anyone?

Jim

idler drive

How about an overrunning clutch, maybe a starter clutch from an old briggs and stratton engine

"How about an overrunning clutch, maybe a starter clutch from an old briggs and stratton engine"

That would be fine, but I should think a simple pony, such as a split-phase, and not a capacitor start, nor a capacitor start/capacitor run, would be OK, too.

Definitely the smallest motor which will start the idler within 1 to 2 seconds, if you're going to belt it.