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Air compressor tripping 20 amp breaker

I have a Sears 25 gallon/4HP horizontal compressor. When I first turn it on it runs fine and shuts off at 150psi. The problem I have is when the pressure gets at the level where it automatically kicks on again it then pops the breaker off and I then have to reset the breaker before it will run again. I have a dedicated 20 amp circuit with 12/2WG using a Square D breaker and a 20 amp duplex receptacle for the compressor, and nothing else is on this circuit. Do any of you folks have any suggestions as to how I can cure this problem? Thanks for your help.

Reply to
Tom
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If this was working and it stopped I would suspect a bad check valve. If it is new you will have to look at the nameplate FLA rating on the motor to see what you are dealing with. The number on the tank label is usually a fantasy.

Reply to
Greg

Hi, There are breakers with different peak surge and trip delay rating, what kind of breaker do you have in there? Tony

Reply to
Tony Hwang

Congratulations, your electrical system is working as it should.

Obviously, the compressor motor has a current surge problem on starting. You have several options: 1) Run it from a dedicated 30 amp circuit, new breaker,

10 ga wire, etc. 2) If it is a capacitor equipped motor, have a qualified shop check and/or replace the capacitor(s). 3) Replace the motor with one more suitable for the machine. 4) Rewire the system to run on 220 volts after ensuring that everything is OK otherwise. 5) Install a smaller motor pulley. That will reduce the starting current modestly, at the expense of slower output (no free lunch, ya know). One or more of the above ought to work. Good luck.

Joe

Reply to
Joe Bobst

Check motor startup peak amp draw with tank empty and as it trips the breaker, You will be suprised. Then contact sears for maximum amp draw guidlines and remedies.

Reply to
m Ransley

What does the manual say the circuit should be rated for?

Reply to
Joseph Meehan

Tony, It says on the Square D breaker

10KA 120/240V-
Reply to
Tom

Make sure the unloader isnt clogged and the check valve is working correctly--when it shuts down, it should hiss for a couple seconds then stop.

Otherwise it will be under too high of mechanical load on startup, not good as it will draw too much electrical current.

Reply to
PrecisionMachinisT

If the machine starts OK with low tank pressure but trips a breaker with some tank pressure (its low pressure limit), then it's almost certainly the check valve, AKA the unloading valve. These don't last forever, and they're really not expensive.

If the motor is trying to turn the pump against existing tank pressure, almost any motor, even brand new, will draw excess current.

Reply to
Robert Barr

You do not mention the distance the circuit is. I assume you ran #12 copper?

Have you checked the connections on the breaker and recpt. An motor can draw

6 times FLA on start up. With an air compressor with partical pressure the high current draw could be lasting longer than the breaker likes.

Try changing breakers with another in the panel. If it still happens then check out the compressor.

Reply to
SQLit

(Correction -- the unloading valve is an entirely different creature than the check valve.)

Reply to
Robert Barr

Tom, does the compressor make a loud hissing noise after it shuts down at

150 psi? This would be the "un-loader" valve. The unloader allows the compressor to start with little of no pressure in the cylinders. This allows for a low starting amps until the compressor gets up to speed. If the unloader is not working, then the full system pressure is adding resistance to the starting load and may be too much for the breaker.

john

Reply to
John Beckman

John When it shuts off there is no hissing noise. It's just quite.

Reply to
Tom

Check to see what the unit is rated at. Does it call for a 30 amp breaker?

Also, you aren't running it with an extension cord are you? I had a neighbor that had trouble with his. Worked fine for years and it started tripping the breaker. He put a new breaker in - same thing. Bought a new capacitor and then eventually bought a new motor. I asked him what he was doing different and he said he was using it away from his shed and had it hooked to a 100 foot extension cord. Bingo. That was his problem.

Reply to
Red Neckerson

The unloader valve should release the pressure from the output line of the compressor as the compressor turns off. If you don't hear the air release, that valve is not doing its job.

Bob

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Reply to
Bob

No I'm not using an extension cord. I go directly to a dedicated outlet from the compressor.

Reply to
Ace

I have a Sears 25 gallon/5HPhorizontal compressor as well and mine did the same thing after about two years. It was on a 20A 110V breaker 5 feet from the panel on a dedicated outlet. I rewired the motor to 220v (simple jumpers and the schmetic is in the motor junction box) and put it on a 20A

220V breaker and has been fine since. When I was having the problem I checked the motor with a megger and checked the amperage of the load and the motor was fine but the startup current was around 22 amps. My guess is that this was due to the fact that it is a oil less compressor and is now wearing in a bit and has become hard starting. It has been fine on 220v and is drawing 8.5 amps on startup.

Reply to
W. Scott Wohlgemuth

That was exactly my problem too. There is a voltage drop if your extension cord is too long. That plus the start-up load trips the breaker. The solution

  1. Use an extra long air hose instead. There won't be any air pressure drop and the tools will work at full power.
  2. Open the air tank valve to release the pressure so that the start-up load isn't high enough to trip the breaker. This is still a poor solution because the breaker will still trip, though less often.
Reply to
PaPaPeng

my god. . . there were only 2-3 guys that gave you the correct advice. it's 1 of 2 things, the unloader as they suggested is bad or if the check valve is not seating , air will be allowed to flow back into the cylinder thus giving the moter a much larger initial load at start up. Do these couple of checks:

1st start compressor and when it reaches it's cut off pressure and stops, loosen the fitting on the steel line going from cylinder to tank. loosen at the cylinder. you should be able to remove the fitting completely w/ out hearing any hissing. IF it hisses, check valve is bad. No hiss = bad unloader, located by your pressure sw. let me know what you find , but theres a 99.9 % chance iit's 1 of those 2 things.
Reply to
Playintennis5274

are you serious ? ? ? and if it trips the 30 should he go up to . . .ohhh maybe 60? Hell just go directly to the power co. feeder. and going to 220 isn't gonna do a damn thing either. if you go 220 then your F.L.A is 1/2 of F.L.A at

110. the moter is draw as much as it can to try and start.
Reply to
Playintennis5274

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