TOPIC:

I have an 3HP 8-gallon compressor I use to seat tires that is blowing breakers. It looks alot like the ubiquitous Campbell Hausfield HL4000. When it starts, it struggles a bit, like a car with a weak battery; then RPMs shoot up to normal, and it'll run for 10 seconds or so, then the on-board 15A breaker pops. It used to be that it would only pop now and then, so you could fill-up the tank by resetting it a few times.

I think the breaker is probably OK, because every now and then, it pops the garage GFI outlet instead of the onboard breaker. The compressor has both a Start and a Run capacitor; both look good (no bulging), and I tested both using the "ohmmeter" method, and they are functional and not shorted. I can't test for the exact Farads capacitance because my multimeter only goes up to 37uF, and both caps are spec'd above that, so it's possible that the "run" cap is working but no-longer in-spec.

I'm wondering what to check next. I could buy a multimeter that goes to 100uF (and get one with Dwell while I'm at it!). Or I could pull the head off... do the reed valves break in a way that would make a compressor blow breakers? If it's more than a reed-valve/gasket rebuild kit, or a new capacitor, then I'll probably just give up and buy a little pancake compressor, and use that to fill the big tank. I only need the big tank when I seat the bead on tires.

I'd check the power drop at the wall receptacle when it starts and runs.
Steve

I used a 2hp 20 gallon Campbell Hausfeld compressor for many years and it would pop the 15A breaker fairly regularly if I used an extension cord. There was a funny hp race some years back with regards to compressors which led to class action law suits so hopefully yours fell into that range otherwise there is no way yours can drive a true 3 hp motor (assuming you are running off 110 VAC power.)

More than one electrician has said that a breaker will weaken with repeated trips, leading to "ghost trips" at lower current. Perhaps the breaker is fatigued?

You also indicate the motor "struggles a bit" on startup. Does everything turn freely, plug and receptacle contacts fit tight with no signs of heat or arcing?

We have an ancient 5Gal. Sears compressor that had a repair in the middle of its power cable that was done sloppily by a PO when we got it. That compressor would trip the 15A breaker in the sub-panel routinely toward the end of it's run as pressure built in the tank until we traced the problem to the cable repair; it would get hot while running, probably because of excessive resistance. We replaced the power cable with 10 ga. stranded and never had any more problems.

If you can get your hands on a clamp on ammeter, that would indicate true amp load. Also, if the compressor is connected to an extension cord, that could introduce additional voltage drop, leading to increased amp draw.

Good Ridin'
slmjim & Z1BEBE

If you set your meter at 200 VAC and plug it into the top of the receptacle you can watch the voltage drop as it powers up then runs. As said the breaker can be weak but you must be sure you're not overloading it. How far is it from the meter?
Steve

Move the compressor closer to the main power. The motors in these compressors are fixed frequency drive, if you move the compressor farther away (i.e. using an extension cord) the voltage drops by the time it gets to the motor but motor frequency has to stay the same so it daws more current, eventually tripping the breaker (and possibly burning out the motor).

If you have a long enough hose or a good 12 gauge extension cord the outlets in your kitchen and laundry room are 20 amp
Bath rooms too