I have an older model electric motor driven compressor that causes my
electrical circuit breaker to trip when the motor kicks in to "refill" a low
pressurized tank. In other words, when the tank is empty and I plug it in,
it starts and works fine, filling up the tank, then stops automatically when
full. After use or when the tank's pressure becomes low, the motor attempts
to start the compressor again, but is not able to. The motor hums for a
short while, then trips the breaker.
The circuit is one a 15 amp breaker, the motor draws less than 11 amps. Any
Have you really checked the motor draw? It can be substantially higher at
start-up than in a steady state situation. I experienced breaker trips for
years in the exact same situation with my compressor. My solution was to
run a dedicated circuit to the shop for the compressor. I think I used a 25
or 30 amp breaker and sized the wire appropriately.
On all compressors there is some sort of unloader that releases the air
pressure at the head or discharge of the compressor pump. My bet is your
compressor's unloader has failed, and does not dump the air at shut off.
Some units have this unloader tied in to the pressure switch, others use a
valve at the tank that looks like a plain old fitting.
The function of the unloader being so the motor doesnt start under
load--allows it to get up to speed before having to do any serious work, as
motor startup draws a buncha amperage as is.
Oftentimes the unloader valve gets clogged with crud from the compressor oil
and simply need cleaning in solvent of some type.
Usually a properly functioning unloader will release a small amount of air
each time the pump cycles off and it makes a short hissing sound at this
warning: thread hijack for another compressor question
i also have one that has a problem. it will go on, charge up the tank to 125
psi and shutoff correctly. however, the relief valve under the electronics
will then open, vent to 75psi, close, and the motor will go on again.
there is another safety release valve screwed into the top of the tank. that
one isn't the one that lets go.
is this also a failure in the unloader? there's a plug in the top that has 2
tubes coming out of it. one goes to the motor, one to the valve that's
giving me the problem. does this plug have some sort of diaphragm that could
be bad? the schematic i have of the compressor doesn't even have this part
listed, so i don't know what it does.
With the unloader that is controlled by the pressure switch, there is a
one-way cheack valve in the compressor discharge line, before the line
enters the tank. Your check valve is stuck open. The function of the check
valve is to stop air from leaveing the tank, flowing back through the
discharge line, when the unloader is working.
Probly a brass plug looking thing screwed into the top of the tank, 1in pipe
threads or so usually--the compresser generally delivers air to it through
copper or aluminum tubing.
The problem is with the compressor.
It is either the unloader or the back check valve, more likely
the back check (on some compressors the same piece performs both
functions). This part is located where the compressor discharge
line enters the tank on many units. Your compressor is trying to
start against the pressure in the tank for which it was never
Keep the whole world singing . . . .
DanG (remove the sevens)
It could be you have a weak breaker. Swap it with another one in the
box (of the same amperage), or just buy another one and try. At most
you'll be out the cost of the breaker, usually around $5, and you'll
have a spare breaker. Motors consume huge amounts of power during
startup. most breakers allow for that. Your breaker may just not be
able to handle it. You could also have a weak/dying capacitor in the
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