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  #1  
Old 11-20-2008, 01:52 AM
milanuk milanuk is offline
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Air compressor keeps tripping the breaker

Hello,

It's that time of year again - time to blow down the in-ground sprinkler lines to get as much water out of them as possible to prevent freezing and splitting, etc.

So, I trundled my Crafsman '6hp' (yeah, right ) 120v 25 gallon horizontal tank air compressor down the stairs to the basement shop and into the back storage room where the isolation valve and connection fitting to the sprinkler line is. Normally this compressor 'lives' up in the enclosed garage, and stays up there for things like filling tires, etc. I have a little Ridgid oil-lubed hot-dog compressor that I use down in the shop for things like nail guns, blowing out dust, etc.

Anyway... I plugged in the compressor and let it fire up (pressure in the tank was almost zero). It ran fine for a while... and then as it got around 95# or so, it tripped the breaker back at the panel. Well, I thought, it *was* plugged into the same outlet as the small chest freezer. I plugged the compressor into a different outlet on a different circuit via a heavy extension cord, and reset the breaker and turn the compressor back on. It ran for a while... and then tripped that circuit too.

I got to digging around, and thought to myself... 'I wonder if the stepson ever changed the oil in this thing like I asked him to'. Pulled the drain plug, and a depressingly small amount of oil came out into the drain cup. I went and found the 30W compressor oil, and filled and filled and filled and filled. I don't have the manual anymore (compressor is about 6 years old) and I've not been able to find one available for download from Sears as of yet. Anyway, I figured the bottom sump area has to be more than full by this point - pretty sure I put in about 4-5x as much as I took out originally. Without a manual and some sort of sight glass I am kind of guessing on this part, which I don't much like.

I plugged it in, and turned it on. It ran... for a while again, and tripped the breaker. Okay, I figured maybe that circuit had too many odds-n-ends plugged into it, so I went to another... ran for a while and tripped again. This time the thermal overload on the motor also tripped. The circuits it had been on before were 15A ckts. Tonight it tripped out even on 20A ckts. I thought maybe it was the voltage drop over the 25' extension cord... plugged it right into the receptacle (no extension cord) - tripped the breaker immediately. Tried another one - same thing.

So... at this point I'm kind of at a loss. *Something* is hosed, or not working as advertised, whether due to running low on oil over a period of time, or something else, and causing the motor to trip the breaker when it gets up to a certain pressure which probably corresponds to a given amount of work/friction/drag that it has to overcome. I'm not really in the mood to disassemble a compressor and go detective on it (although I may after finding out what it'd cost to have someone else do it!), so I'm open to suggestions. Who would you call at this point - Sears, a motor shop, some place else?

Thanks,

Monte
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  #2  
Old 11-20-2008, 08:54 AM
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Wish I knew enough about compressors to help. I have a friend that rebuilds compressors and resells them, I am copying your issue in an email to him, maybe he can help?
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Old 11-20-2008, 09:12 AM
cabinetman cabinetman is offline
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If the compressor ran without tripping the breaker in the past, there must be some "new load" causing more of a draw when the pressure builds up. Extension cords can be a cause, as well as too tight of a drive assembly, plugged air filter, or debris in or around the motor causing it to run hot.

Extended run times may indicate a leak somewhere which would prevent the tank from filling to the point of "pressure release". Other things to check are poor connections at the breaker, outlets, cord/plug, and internal connections at the switches on the compressor.

As for oil levels, many compressor crankcases are designed for a "spill out" when full. IOW, the oil is added until it fills to the top of the fill hole. There should be enough space left for the plug to be inserted without displacing oil.
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Old 11-20-2008, 09:29 AM
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If the compressor runs OK in a location where you are certain the circuit and wiring are of adequate capacity, but pops the breaker in your basement location, suspect the circuit is overloaded, or the wire size too small/distance too great.

If this same compressor has run out fine before in the basement, and you are certain there is no extra load that was not present before, suspect the compressor running harder or the breaker has gotten weak (it happens).

The fact that the compressor is building pressure to a point before the breaker trips would make me look at something else, rather than the compressor, although it still may be the culprit.

Let me point out, without prejudice, that if you replace the breaker, make sure it is with the same size unit. Do not be tempted to get one size larger to make that nuisance tripping go away. You'd be surprised just how many people think the answer is to do exactly that. Your breaker is sized for the capacity of the circuit wiring, and is supposed to be the weak link. They do however get "tired" sometimes, particularly if they have operated routinely near their rated limit, and can actually start tripping at much lower than their intended overload point.
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Old 11-20-2008, 09:41 AM
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Compressors don't like extensions cords. Try plugging it into the outlet without using the extension cord.
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Old 11-20-2008, 10:48 AM
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The garage where the compressor normally 'lives' has its own sub panel with next to nothing on it - some lights, a wall-mount heater, and an exhaust fan. The previous owner had a Victor 16x60 gap-bed engine lathe where my compressor is sitting now - so I'm pretty sure it's the only thing on that outlet circuit right there Unfortunately its not as simple as just rolling it back up there to test it out - it takes two healthy people to haul it up the stairs.

The downstairs shop area where I had it plugged in for this little blow-down event has a fair number of outlets, but typical of household wiring... its not labeled well (I'm working on that) and kind of hard to tell which outlets are scabbed together on which circuits. Case in point - one of the 'ceiling' outlets I had the compressor plugged into that it tripped is also the circuit that feeds the switched outlets (floor lamps) upstairs in the living room. I know because SWMBO hollered at me when her lights started flickering and then went out as the breaker tripped

As mentioned, I did plug the unit straight into a receptacle last night, no extension cord.... instant trip of the breaker. The starting current once up above ~100# seems to be dumping the ckt pretty quickly. Almost like an unloader valve isn't working or something.
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Old 11-20-2008, 11:38 AM
Uncle Cracker Uncle Cracker is offline
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Sounds more and more like your circuit is just not hefty enough to handle the compressor, while the one upstairs apparently is. Your circuit breaker is probably just doing the job it was intended to do, although it still may be a weak breaker. You could try switching the wires in the breaker box with another breaker of the same rating. If the problem goes away, replace the breaker. If the swapped breaker also trips, then the compressor's too much, although that doesn't necessarily mean there's something wrong with it.
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Old 11-20-2008, 12:25 PM
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Guess I'll have to get some help and haul that beast back up the stairs to the garage and see if it still works okay in there (it doesn't get used all that often).

I think one thing that may come of this is going to be some dedicated tool outlet circuits in the downstairs shop... haven't had too many problems with other tools (well, the DW735 planer has tripped the breaker on an outlet string a couple times), but I think the peace of mind of being able to know that a tool is adequately supplied might be worth it.
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Old 11-20-2008, 01:13 PM
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i think the first order of business (as you've already concluded) is to make sure the units runs or fails at the last known working location/plug outlets.

If it doesn't fail then you've go some wiring issues in the basement.

It its now failing then there's too much load on the motor that's not normally there.
Maybe you damaged something running real low on oil. Or, maybe some check valve/unloader valve is broken. Though this would usually manifest itself as a problem in starting up when there's already some pressure in the tank.
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Old 11-20-2008, 05:22 PM
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Until I upgraded my circuits, I had difficulty with my 24 Gal HF compressor, blowing the breaker. It would run fine until the tank was nearly up to 120. The motor would labor under the additional pressure and pop the breaker. Until I had a new circuit installed I lowered the regulator to 100 lbs and it did not trip the breaker.

Steve
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