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.
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.
Congratulations, your electrical system is working as it should.
<< Do any of you folks have any suggestions as to how I can
cure this problem? >>
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.
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.
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
Otherwise it will be under too high of mechanical load on startup, not good
as it will draw too much electrical current.
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.
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.
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.
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.
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.
I was also thinking start up load. Sometimes the electrical switch has an
adjustment, so you can set the "turn on" pressure down a bit lower.
Or you can make a pinhole leak right after the compressor, so that when the
comp starts, it's under zero pressure. Needs a check valve after the pinhole
Best bet is to check the volts and amps at startup, and see if that tells
you something useful.
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.
HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.