On Sep 25, 6:31*am, "Dennis" wrote:
I picked up a small fridge compressor with the idea of playing around using
it for a vacuum pick up tool for small electronics parts, but it behaves
strangely.

On initial power up it runs fine, very quietly.

It quickly/easily pulls down to 20kpa (-80kPa).

However if I disconnect the power and reconnect there is a quiet hum like
the motor is stalled (motor is not running & there is no airflow).

If I disconnect again then wait a minute or two before reconnecting it
powers on fine and will run fine - I've let it run for 5 minutes
continuously with no problems.

As part of the terminals to the motor there appears to be a thermal overload
switch, it gets warm but not hot (my guess ~30 Celius)

Heres a link to the data sheet:

http://www.transtech-co.jp/electroni...ompressor7.pdf

I vaguely recall something about fridges having protection against rapid
cycling of the power for some reason - but that could be rubbish. If there
is some sort of anti-short cycle timer it must be inside the compressor
housing itself.

Any ideas?

Thanks.

The link (page 7 only) did not have a wiring schematic. But hermetic
compressors use induction motors. There should be a start relay (most
likely a positive temperature thermistor, in series with the start
winding).
Yes the motor is stalled, because the pressure must equalize between
power on/power off cycles, as there is very little starting torque in
these motors. This is true for refrigerators and air conditioning
units.

ignator