View Full Version : Problems getting rpc started

05-12-2009, 01:34 AM
Hello All, I'm new and found this site because I'm having problems getting an rpc up and running.

I've got everything roughed together and wanted to test it out before hardwiring. Although it will eventually be capacitor start, I have been trying to start it with a rope. I wanted to make sure I could get the motor to start and run by itself before adding the capacitor start circuitry.

My symptoms are that the motor vibrates quite a bit, never gets above ~150rpm est., and will eventually cause the breaker to trip within about 5 seconds. The wiring on the L1 lead only gets hot enough to melt the (temporary) electrical tape connection. L2 and phantom L3 stay cold, the capacitors are not warm to the touch. I'm using 2 banks of run capacitors, 160uf each, between legs 1,3 and 2,3. Yes, I'm a bit below the 12-16uf/hp rule of thumb at this time, my understanding is that this should not have any effect other than not perfectly balancing L3.

I'm using a 15 horse wye-wound motor, Baldor CM2513T and the contactor is rated at 15hp single phase 208V. My connections to the motor are as follows:
(L1,9,3 and one wire from cap bank)
(L2,2,8 and one wire from cap bank)
(1,7, and both remaining wires from cap bank)
Capacitors are all connected in parallel.

Please help if you can. I'm a diy'er doing my best to figure this out for myself. I'm attaching a word file showing my setup. Yes, it is a test setup only and will require proper hardwiring to be safe. Thanks in advance!

05-12-2009, 10:15 PM
Figured it out. Turned out to be two things. The heat buildup and smoke was due to a poor connection to the motor wiring from the input power. Once that was corrected, it still wouldn't reach speed and was blowing the breaker while trying. I connected up my start capacitor circuit and it started just fine.

I have about 20 minutes of run time now with everything staying nice and cool and the motor sounding good. Power appears to be pretty balanced using 160uf between each leg, within 5-7 volts unloaded. I will load test it next week and may make slight adjustments based on the results.