"Dennis" wrote in message
...

"ignator" wrote in message
...
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

==================================

I had a good look around and could not find a full data sheet, even
ferreting through the chinese language website didn't help.

I pulled the pump out of a very small refrigerator (probably 20 Liter
capacity). The wiring was very simple and looked like it just went via the
thermostat then direct to the compressor. Is the thermistor likely to be
internal?

When I tried to restart the motor it was with the intake & exhaust both
open to ambient atmospheric pressure. Is there pressure internally that
needs to bleed back or something to reduce the required starting torque?

Thanks for the reply.







I found a wiring diagram on the frige metal work.

http://www.metalworking.com/dropbox/VacPumpWiring.JPG


It shows an overload protect device. The overload and the start cap are
inside or at least part of the compressor. There is a small plastic cover on
the side of the compressor, I'll pull it tomorrow and see what it conceals.