I got a call from a good customer of mine today regarding a slurry pump issue. This is a 16 hp 230V single phase submersible pump. It has a control panel with capacitors, circuit breaker, contactor, and a relay. The pump wouldn't start, and tripped the breaker upon trying to start.
I found that the coil on the start capacitor contactor was bad. So, I robbed the contactor from his spare control panel. When I engage the switch to start, the capacitors snap. Why???? When I left it running for about 3 seconds, one start capacitor started boiling.
So, I decided to install spare panel. Now the pump just hums and sometimes snaps at the run capacitors. Why??? It acts like a bad start circuit but all capacitors check out o.k. It is driving me crazy that I can't seem to figure out why this won't work.
Yes, the pump was pulled and checked. It was free with no mechanical binding. I did ohm all the leads with no short to ground and phase to phase resistance. The strange thing is that it ran once until the caps started boiling. That is when I decided to switch to the spare identical panel.
Electrolytic caps do not like AC current. When the dielectric fails, they become resistors and the electrolyte usually boils and vents. I suspect that the start cap is failing because the starting circuit is remaining energized. That points to a centrifigal switch not opening up or an insulation failure between the start cap and motor frame or earth.