Time for a new rotary phase converter. This one is 20 HP. It's balanced,
but to avoid the monstrous starting surge current, I spin the idler up to
speed with a 1HP single-phase pony motor before kicking in the idler
contactor.

Here's the strange part: while the idler is running the pony motor
housing gets hot. I don't understand why. It's a continuous-duty rated
motor with good bearings. It's an old pool-pump motor that had a bad
start cap.

Now, it *seems* like the heat is coming from the stators -- what you'd
expect if the motor were powered up and driving a load. That is, the heat
isn't concentrated around the bearings, but seems to be coming from the
body of the motor. But, whenever the idler contactor is engaged, the pony
motor contactor is disengaged. I double-checked and there is no line
current into the pony motor when the idler is running.

WTF, mate? Eddy currents? Leftover heat from startup slowly making its
way out to the case? ???

Jim