One trick worth trying is to put a pretty good sized (say, 100 amps or so)
load across the contactor when in the closed position and then open the
contactor. The arc thus formed will be enough to melt any oxidation on the
contacts and you will be left with a fresh metal surface nearly as good as
the original.

Do NOT put the load across the line and then turn the contactor on. You
have every chance of welding the contact surfaces together.

Jim

"rich" wrote in message
...
My homebuilt's master contactor is going bad. Sometimes when I turn it
on it doesn't make connection. It's got 1700 hours on it, so I'd just
as soon replace it. But the way the builder wired it, he's has
positive power from the battery going through the master switch to the
small terminal on the contactor. (cole-Hersey type) But the master
contactors, such as Spruce sells, are set up to actuate with ground
power going to the small terminal. They also have plastic around their
mounting feet so their case doesn't make ground. A starter contactor
would work perfectly with the way the plane is wired. I just wonder,
are starter contactors made to withstand continous use, like a master
contactor does? And how can one tell the difference in the two, they
look identical? And if not, can the master/continuous duty type be
made to work with postitive power to the small terminal?