On Thu, 04 Mar 2010 05:13:31 GMT, lid (Sparks
Fergusson) wrote:


I'm having a problem with my 20 gallon, single stage electric air
compressor. It's acting like the motor is underpowered - it pumps up
to about 95 psi ok, but then the motor stalls. The unloader bleeds the
pressure off, the motor restarts, runs for a couple of seconds, and
then stops again...repeat...repeat...

It worked fine for years (The pressure switch would shut it down at
about 120 psi) but over the past few months, it's gotten worse and
worse, and now will only make about 90-95 psi before the motor stalls.

I cleaned and lubricated the compressor itself, and it spins freely
and doesn't appear to be binding or otherwise have excessive friction.
The check valve/unloader is working and the piping is all open and
clear.

It seems like the electric motor (1/3 hp) just no longer has the oomph
it used to. It starts up fine, no humming, no smoking, no bad smells,
no clunks. It just doesn't seem to have enough running torque to
handle the load like it did before.

Anyone have any ideas?

Thanks!
After reading all the posts, several things stand out. The most
significant: There is no excessive current draw when the motor stalls.
By all the laws of physics, that is flat out impossible. There are
two explanations (well, three, but I'm assuming you aren't making this
up). The first is slippage at the belt, motor pulley, or rotor.
Given the knowledge you have exhibited, I say that can't be the
problem; it's pretty hard to miss the fact that the motor is spinning
but the belt is slipping.

That leads to only one conclusion: The actual voltage to the windings
is dropping. Possible causes are a bad thernal overload protector,
bad run capacitor (some motors hide the starting capacitor inside,
while the run capacitor is in a cupola on the side), or a corroded
terminal so only one of the paired windings is used.

All of these possible causes result in a lot of heat generated at
one small point EXCEPT the single winding and the bad run capacitor.
The single winding explanation is unlikely because it would not
deteriorate gradually. That leaves the bad run capacitor.

PlainBill