RPC Third Leg Voltage

[Scra99tch]

Is their a way to calculate the voltage you would get off the third leg without being connected to a load? I picked up a RPC from a junkyard that had the box ripped off and 8/10 caps were bad.

I replaced the caps and fire it up and was able to measure the third leg at a higher voltage. Just wondering what that voltage would be +/-

Also what would cause the caps to go bad like that, a power surge? They tops were bent outwards like all electrolytic caps are when they sh*t the bed.

The supplied voltage is 220 and its a 20HP motor.

Thanks

 

[JimDawson]

It depends on the balancing caps. Mine runs about 10 volts high (250V or so with 240V input) unloaded. But settles back down to about line voltage when loaded.

Who knows what happened to the caps. Maybe a voltage surge or maybe they just got tired.

 

[markba633csi]

Capacitors go bad after a long period of use, but poor quality ones go faster.
Also, disregard the third leg voltage under no-load conditions.

 

[John_Dennis]

I was figuring all of this out a few weeks ago, because there is not a normal relationship between the 3rd leg and the neutral, there is no way to measure that. The voltage between 1 and 3 and 2 and 3 should be similar. The voltage between 1 or 2 and 3 is typically lower than between 1 and 2 but everything changes based on load.