Belted Pony Motor RPC

toolnut · Jul 10, 2008

I am hastily putting together a belted pony motor RPC for another PM member. I have not built this style before and believe I understand how the single phase motor will perform but thought it worthwhile to ask.

Are there any concerns about using a capacitor start pony motor? This will likely be a 1 hp pony motor to start a 15 hp idler. As I see it, the centrifical switch will keep the capacitor out of the circuit anytime the idler is up to speed. If this is correct then the capacitor should have no effect on the system once the switch opens. With this design, the pony motor spins all the time the RPC is in operation, but is under power only for starting.

Bruce Norton
Kingsport, Tn

gpkull · Jul 11, 2008

the pony is only to get the rpc up to speed. there is no need to leave the pony hooked up. why would you want too? i think some one is behind on the home work

jim rozen · Jul 11, 2008

I do take the belt off of my pony motor, once the idler is running.

Jim

DaveKamp · Jul 12, 2008

Behind on homework?

Gee, I read the initial post several times, and don't see where he'd be considered truant in homework performance... noted that it's still spinning, but not powered.

Frankly, I don't see any reason you'd need to even disengage the pone-motor, aside from cutting down on bearing wear. if you wanted to make a pony-start 15hp unit self-starting, you'd really only need a centrifugal speed-detector on one of the shafts, and once running, disable the start motor and activate the main motor...

wippin' boy · Jul 12, 2008

==========================
"I do take the belt off of my pony motor, once the idler is running.

Jim"
==========================

yes
but your system is of a level of sophistication not available to all of us Jim

Lifting up the hinged platform allows the belt to fly
off.

jim rozen · Jul 12, 2008

I mentioned the "remove the belt is best" approach only because one poster here
had the odd situation where he was developing eddy current heating in the pony
motor while it was running, even though it was not powered. Or so I seem to
recall. It was an odd kind of motor I think.

Jim

Carl Darnell · Jul 12, 2008

My RPC uses a pony motor to start it. I used pulleys the right diameter to match as close as posible the speed of the RPC. I still turn the pony motor off after the RPC is up to speed and on line. It serves no purpose to remove the belt as both the motors will last longer than I will and if not I can repair them. If you leave the pony motor on that is another current drain to deal with.

All my switching is manual so I have to be awake and allert when starting up.

DaveKamp · Jul 13, 2008

Removing the belt...

Jim- interesting that you mention that...

...but I understand why that would happen. There are two-phase motors, and a few other centrifugally-switched cap-starters out there, and some brush-type AC motors (not so-called 'universal', but similar) that, if you spin 'em, they'll contain enough residual magnetism to become little generators. IF they have enough going, and there's starting caps, or a shunt-winding, they'll start sending current through themselves, becoming a parasitic load... and the result... a heating motor that isn't being powered.

Cool (er... hot) situation to mention... not common, but should not be ignored.

jim rozen · Jul 13, 2008

I swear this happened to a poster here long ago. I think peter H. was the person
who figured out the puzzle, and how to fix it.

Jim

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