Perhaps my statement:

"It may be possible to start a 10 HP, or so, idler with capacitors but I
think starting a 40 HP motor with capacitors alone is out of the question.
Someone on RCM a while back said he was starting a 15 HP idler with no
problems." should have been more clear. I should have pointed out that
running motors of 10 HP or greater on ordinary residental service is likely
to require larger circuit breakers than normally provided in residences.
Circuit breakers are sized for full loads. A rotary phase converter "looks"
much like a single phase motor in operation - but not an ordinary single
phase motor. RPCs draw large leading currents in proportion to their size,
and it is unlikely an RPC of much over 5 HP, with full load, could be
operated from a 30 amp residential-size breaker.

Note that Pete's 30 HP, capacitor started idler, was fed from its own 240 V,
100 amp (dedicated) panel. I'm sure it started and ran OK but he probably
never loaded it up to near its capacity. A fully loaded 30 HP RPC would
require more than the 100 amp capacity of Pete's panel.

Bob Swinney


wrote in message
oups.com...

Mark Main wrote:
Why are you looking for an 8 or 16 pole idler motor?

My goal is to have 20 HP available and so I sized my idle motor at 2
times that; and it appeared from my reading that more poles would have
the advantage of easier start and slightly improved stability for the
3-phase power. If I'm wrong let me know. My hope is that 8 or 16
poles on a 40 HP will make starting difficulty closer to a 10 or 15 HP
2 or 4 poles.


Yeah, I'll probably have to go with the pony motor. If I can actually
find a 16 pole motor then it will be interesting to play with it to see
if I can get it going with larger capacitors. I'd like to avoid the
pony motor if possible...I can be stubborn when I have a goal in mind.
g probably a trait shared by many who play with metals.

I've used a 30 HP RPC for years, and always started it on just the
capacitors. It was a 4 pole (1750 rpm) motor. It was fed from a 240V
100 amp panel. No problems for me.
I don't see why you need anything more than a 4 pole motor. Unless you
have a big grudge against your wallet.
No pony motor, Just about 2000 MFD to start. THUMP!. Running. Cut
metal.
Pete