A much better idea would be to find a datalogger that can monitor 0 to 5VDC
and an amploc hall effect current sensor.
http://www.ampsense.com/AMP25.html These things cost about $5 and need a
stable 5V power source like an Artesyn AFC5-12S05F, 2 little resistors and a
small capacitor. Loop one of the compressors power lines through the sensor
and you can monitor not only when it turns on but how many amps it is
drawing. With that information you can adjust the speed of the little
Danfoss compressors to get the most cold for the least amps.

If you can't find the Artesyn you can have one of my spares for $12.

--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com

"GBM" wrote in message
...
Some of the dataloggers have the possibility of monitoring an event such
as
a switch on/off, but not all.

I think I have finally come up with a simple method - I will just use two
independent temperature loggers. One in the ice-box and one just above the
condenser fan. The latter will get an upward spike in temperature when the
compressor comes on. This way, I should be able to plot box temperature vs
compressor on/off cycle. This should do it.

Thanks for the input.

GBM

"nimbusgb" wrote in message
oups.com...
simpler is to take a couple of turns of the positive feed to the
compressor round a reed switch. Pump on, reed closes, pump off reed
opens. A lot simpler than having to read the current.

Ian M