View single post by Keinokuorma
 Posted: Sun Jan 21st, 2007 01:14 am
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Joined: Mon Jun 26th, 2006
Location: Finland
Posts: 1248
 Not sure if I'm exactly following what you wrote. But if I am only measuring 5 ohms, does that mean the compressor is drawing something like 25amps at 125Volts?
No. There will be inductance. That leads to reactance, which is frequency dependent. Inductive reactance is proportional to frequency. Trigonometrically summed up with the resistance, you get impedance. Assuming that the compressor run winding draws 3A at normal running status, we can calculate that the impedance of the winding at 60Hz is 125V divided by 3A, result is 42 Ohms. But your meter will say it's 5 ohms because you're measuring at zero frequency.

The bottom line is, if you want to know the current draw, you can't calcualte it plainly by voltage and resistance in this case. Were you measuring a dryer or range element, or light bulb, things with next to no inductance, that would be plausible. but in this case, you must go right to the spot and measure the current. Clamp-on meter isn't as invasive as the conventional method where you connect a meter in series with the load.
So since the compressor runs for a few minutes and doesn't just shut off when I temporarily hook it up the way That Guy suggested, I guess I'd like to check out how to hook up the 3-in-1 to see if it will run for an extended period of time. I can't seem to figure out how to hook it up correctly though. Any ideas on how to do it?

 Why not try the wiring above. This is of course a simplified system with no defrost system etc... but most of the cheap-o Yurup fridges are done just like this. Much can't go wrong with any rocket science elecronics there. Just plainly thermostat turning comp on and off, and the door switch only operating the interior light. But the wiring between the relay and compressor is what we need of this. And, with your supco relay, the packaging slip shows just this. Two wires for power, three for comp. Thermostat controls power to the relay.

Note that in this diagram PE stands for Protection Earth, or just Ground. Its only purpose is to keep the chassis potential at ground potential. Also the L/N polarity should not really make a difference in a healthy system.

Last edited on Mon Jan 22nd, 2007 01:52 am by Keinokuorma

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