Air Compressor Intermittent Failure to Start and Run

[kjohnson1]

Campbell Hausfeld 80 Gal Compressor
Pump model: FP070000AV
Motor Number: BM74

Not every time does it fail to start. Just sometimes. It does not trip the circuit breaker. To start it I go to the circuit breaker, turn it of then back on.

Motor capacitor is within spec. Other than the intermittent start and immediate crash, everything works just fine.

 

[Trey T]

If it fail to start, can you "safely" assist to start the pump flywheel to get it going?

 

[C96]

Not every time does it fail to start. Just sometimes. It does not trip the circuit breaker. To start it I go to the circuit breaker, turn it of then back on.

Motor capacitor is within spec. Other than the intermittent start and immediate crash, everything works just fine.

Sounds like what you are actually describing is resetting a tripped circuit breaker.

Sometimes a tripped breaker doesn’t always appear to look as though it’s in the tripped, or off position, but in fact it is.

It’s very possible the compressor is not unloading the head pressure after it shuts down from completing a pump-up cycle. This will cause significant stress on the electric motor when the compressor tries to re-start again often resulting in a tripped overload protection device, or tripped circuit breaker.

Again, you stating having to switch the circuit breaker to the off position then back to the on position in order to get the compressor to start is typical of resetting a tripped breaker.

 

[redmondjp]

I'd say that you have a defective circuit breaker. They do go bad. It may not be tripped, but could have a high-resistance contact inside of it that is temporarily cleaned by flipping it off and on again.

Replacement breakers are inexpensive. I'd change it, and pick up a few other spares for your panel. I've changed out a few of my 1977 GE circuit breakers for similar reasons (when you hear buzzing/crackling/sizzling sounds coming from inside of a circuit breaker, well, obviously this isn't good).

 

[mikegt4]

Swap a breaker from another spot in your panel (same rating of course) and see if the situation improves.

 

[Charles (in GA)]

Does the compressor make a loud hiss from the pressure switch when it shuts down? If it does not, then it is not discharging the pressure off the head in preparation for the next start. This will overload the motor the instant it tries to start. You could also have a pump to tank check valve (Usually found where the pipe enters the tank) that is leaking, so that the tank pressure leaks back into the head after the compressor shuts off. Again, this is overloading the compressor on shutdown.

Could also be a weak or undersized breaker. If the FLA amp draw of the motor is close to the breaker capacity, it is probably being overloaded on startup. Code allows the upsizing of breakers supplying electric motors, up to 250% of the Full Load Current rating of the motor. Is the whole circuit undersized? (wire size and breaker size?)

 

[kjohnson1]

I think you nailed it. Today when it happened again I listened very closely. The circuit breaker did trip, it just did not flip all the way to the 'OFF' position.

Sounds like what you are actually describing is resetting a tripped circuit breaker.

Sometimes a tripped breaker doesn’t always appear to look as though it’s in the tripped, or off position, but in fact it is.

It’s very possible the compressor is not unloading the head pressure after it shuts down from completing a pump-up cycle. This will cause significant stress on the electric motor when the compressor tries to re-start again often resulting in a tripped overload protection device, or tripped circuit breaker.

Again, you stating having to switch the circuit breaker to the off position then back to the on position in order to get the compressor to start is typical of resetting a tripped breaker.

 

[kjohnson1]

This is a possibility I did not consider but should have. Given the proliferation of Chinese goods in our country coupled with their very questionable quality and my refusal to buy 'Made in China', it should have been a suspect early on.

QUOTE=redmondjp;4615463]I'd say that you have a defective circuit breaker. They do go bad. It may not be tripped, but could have a high-resistance contact inside of it that is temporarily cleaned by flipping it off and on again.

Replacement breakers are inexpensive. I'd change it, and pick up a few other spares for your panel. I've changed out a few of my 1977 GE circuit breakers for similar reasons (when you hear buzzing/crackling/sizzling sounds coming from inside of a circuit breaker, well, obviously this isn't good).[/QUOTE]

 

[kjohnson1]

Yes, the loud hiss does happen when the compressor shuts down. I will have to look at the wire size and get back, however I did myself install that breaker box and I 'usually' go overkill on the wire gauge. The breaker is Eaton BR240 40Amp.
Model Number: BM74
Brand: Emerson

Description: OEM to CAMPBELL HAUSFELD CO Customer part # MC024500AV
Capacitor Start- Capacitor Run;
DM motor type; 7.5HP; 3550 RPM; 60Hz; 230 Volts;
184T Frame;
ODP; 31.4 Amps;
1.15 SF;
Standard Efficiency;
Rigid; Insulation Class F; 40 C Ambient; 17.91 C
Dimension; 1.125dia x 2.88 Shaft size;
Ball Bearing

Does the compressor make a loud hiss from the pressure switch when it shuts down? If it does not, then it is not discharging the pressure off the head in preparation for the next start. This will overload the motor the instant it tries to start. You could also have a pump to tank check valve (Usually found where the pipe enters the tank) that is leaking, so that the tank pressure leaks back into the head after the compressor shuts off. Again, this is overloading the compressor on shutdown.

Could also be a weak or undersized breaker. If the FLA amp draw of the motor is close to the breaker capacity, it is probably being overloaded on startup. Code allows the upsizing of breakers supplying electric motors, up to 250% of the Full Load Current rating of the motor. Is the whole circuit undersized? (wire size and breaker size?)

 

[redmondjp]

Motor starting current is most likely tripping the 40A breaker. 32A is maximum full-load current (80%) on a 40A breaker as well so you are right at the maximum load on that circuit.

You may need to upsize wire and go to a 50A breaker if the replacement breaker does the same thing.

You also may want to carefully check all of your electrical connections in the motor circuit (one local compressor technician/rebuilder I know does NOT use wirenuts at the motor junction box - only split bolts heavily taped, due to high-resistance connections from the wirenuts), as any additional resistance in the circuit can cause the motor to take longer to start meaning that it will draw a high current for a longer time (which can cause breaker to trip).

Another thing to check is oil temperature in the compressor crankcase. If really cold, this can significantly increase the motor starting current. In this situation you can either go to a thinner weight oil and/or synthetic.

 

[kjohnson1]

50 Amp breaker fixed the issue. Thank you very much. New problem. Sounds like a rod is knocking....loud.