romeyn

I have a Bell & Gossett series 100 booster pump. The motor/power pack shuts down after 5 seconds of operation, cools down, runs for 5 seconds, etc.

The motor makes no abnormal noise, and this happens even when it starts cold. I suspect a failure of whatever mechanism it is that detects and determines that a thermal fault has occurred. I've confirmed that the power reaching the motor is constant, and I've removed it from the pump with the same results.

All the manuals for these system offer little to nothing in the way of servicing these power packs beyond oiling and replacement of the motor mounts. The mounts on this unit are in good condition, and it's been oiled. Does anyone know if it's possible to "fix" this problem beyond replacing the entire power pack?

CraigFL

Does the motor use a capacitor to start? If it does, I would replace it. If not, the motor is bad or the load is too high for some reason...

romeyn

Please excuse my ignorance. I know what a capacitor IS, but not sure of its implementation in this context. Are you referring to something external to the motor, or something inside it? I have had the motor apart and there is "something" at the far (from the pump) end that's part of the circuit.

It that something is the capacitor, where could I look for a new one, assuming I can manage to remove and replace it?

kok328

There are a few possibilities here:
1) the motor is bad
2) whatever load the motor is turning, is binding up and causing the motor to trip the thermal overload. Once the motor cools and the overload resets, the motor tries again. Check the load resistance manually.
3) a bad capacitor (if applicable)
4) you may have misplace a wire upon reassembly of the motor. perhaps wired it for alternate voltage if applicable. Does the nameplate indicate hi/low voltage wiring options?

romeyn

Thanks for the reply.

1) Perhaps. But for the brief period that it DOES function, it appears to do so normally. No abnormal noise or apparent struggling.

2) I can spin the pump's shaft freely with my fingers. (The motor drives the pump.) This also happens when the motor is disconnected from all load.

3) See my question above, please. This seems most likely to me!

4) No wires were removed when I disassembled the unit. In fact, I'm not even sure it's POSSIBLE. These things are built like brick outhouses! Probably why there are no parts listed for them anywhere. :-(

CraigFL

Usually capacitors are mounted outside of the motor and across the motor leads. They tend to be metal cans with two terminals about 2" X 4" X 1"

CraigFL

You may have to check the motor current to see if it is within the nameplate rated current. This is usually a good indication if there is a problem. If it is within nameplate current, you may have a bad overload sensor. When the motor circuit trips, is the motor HOT??