|
Post by turbokinetic on Mar 14, 2018 2:16:31 GMT
Rheem used to use a dual run capacitor in their central ac units. The 1/2 was in circuit with the contactor open and bled a controlled amount of power through the start winding to warm the compressor and keep from adding a heater. I always though it would not work as good since the motor was on top but the metal of the motor and pump must conduct the heat well enough. That's a good and simple way to do it. For an outside unit, that would surely be great! I would worry that the AC current injection through the capacitor would cause humming which could be objectionable in an indoor application. But might be worth trying!
|
|
|
Post by blackhorse on Mar 15, 2018 17:52:58 GMT
Rheem used to use a dual run capacitor in their central ac units. The 1/2 was in circuit with the contactor open and bled a controlled amount of power through the start winding to warm the compressor and keep from adding a heater. I always though it would not work as good since the motor was on top but the metal of the motor and pump must conduct the heat well enough. This was exactly what came to my mind. Given the much smaller motor size, I'd use a 5 Ufd motor run capacitor, wired across the thermostat terminals so it was "always on". If the compressor wasn't barely warm after 24 hours then try 10 Ufd. (It would be warming the run winding instead of the start winding, but the wiring would be WAY easier than trying to jury-rig something that cut in and out with the compressor cycles.) I have used DC to dry out flood-damaged electric motors. Be aware that it takes WAY less voltage to put a DC current through an AC motor. (This is a good thing when the windings are wet.) And since the motor isn't running, the normal run current will probably overheat it. Given the consequences if something went wrong I'd probably still go with applying heat externally though.
|
|
|
Post by turbokinetic on Mar 15, 2018 21:03:50 GMT
Rheem used to use a dual run capacitor in their central ac units. The 1/2 was in circuit with the contactor open and bled a controlled amount of power through the start winding to warm the compressor and keep from adding a heater. I always though it would not work as good since the motor was on top but the metal of the motor and pump must conduct the heat well enough. This was exactly what came to my mind. Given the much smaller motor size, I'd use a 5 Ufd motor run capacitor, wired across the thermostat terminals so it was "always on". If the compressor wasn't barely warm after 24 hours then try 10 Ufd. (It would be warming the run winding instead of the start winding, but the wiring would be WAY easier than trying to jury-rig something that cut in and out with the compressor cycles.) I have used DC to dry out flood-damaged electric motors. Be aware that it takes WAY less voltage to put a DC current through an AC motor. (This is a good thing when the windings are wet.) And since the motor isn't running, the normal run current will probably overheat it. Given the consequences if something went wrong I'd probably still go with applying heat externally though. Yes, everything has its strengths and drawbacks. I like the idea of a capacitive current limiter circuit to warm the motor, but I would have to advise about one thing. This is from experience two different ways. I built a speed reducing circuit for a small fan using this principle. The circuit had 3 capacitors in it of varying values. A rotary switch would switch more or less of them into the circuit. The problem was, when the switch would close the capacitor into the circuit, there was a snap from the high impulse current. It was quickly damaging the contacts of the switch, to the degree it would weld the switch and stop me from turning it, briefly, then break away and move on. I know that had to be really eroding the contacts. The second issue was adapting a run capacitor to a motor which originally had only a start capacitor. The centrifugal switch would bridge the two capacitors together when the motor would come to a stop. This repeatedly welded the contacts together and caused the destruction of the start cap when it couldn't switch out of the circuit. Motors with a start and run cap from the factory often have two separate start winding taps. One of them is for the start cap (with centrifugal switch) and the other is for the run cap. there are a few turns of winding in between the taps, which have enough inductive reactance to calm down the current spike when the caps connect together. My worry is that allowing the thermostat to bridge across the capacitor to start the compressor would cause some serious contact wear to happen. If the thermostat had a double-throw contact, where it could select the capacitor feed OR a straight feed, life would be grand! I have a feeling that Rheem got away with this because their compressor contactor was "so beefy" (because of the current it had to pass anyway)that the capacitor discharging wasn't enough to really affect its life. The original idea with the DC warming supply could be adapted - keep the relay, to select between power or capacitor - and allow the thermostat to power just the relay coil. Either way you're adding complexity to the system. However, for those of us who don't run their fridges all the time and worry about cold starts; or like myself who has an unheated shop office where they are; either way could be an option to extend the life of the compressor.
|
|
|
Post by ckfan on Mar 16, 2018 0:21:58 GMT
Wow, this is getting complicated fast but I do love the discussion. I’m nowhere near bright enough with electrical knowledge to make any suggestions but what you both said makes sense. The last thing I want to do is to ruin the contacts on the thermostat but simply wiring a capacitor to the thermostat is a very simple solution. Hmm...didn’t someone also mention a heated wrap that could be put over a compressor?
|
|
|
Post by turbokinetic on Mar 16, 2018 0:34:52 GMT
Wow, this is getting complicated fast but I do love the discussion. I’m nowhere near bright enough with electrical knowledge to make any suggestions but what you both said makes sense. The last thing I want to do is to ruin the contacts on the thermostat but simply wiring a capacitor to the thermostat is a very simple solution. Hmm...didn’t someone also mention a heated wrap that could be put over a compressor? I'm sure you could get a pipe tracing and wrap it around the compressor! That's a nice simple solution, too. Just would be immediately visible looking at the unit; whereas the other electrical solutions would blend in a little.
Not sure what the shortest one they commonly sell is, though. I bought one from Lowe's a couple years back and it was too long and had to be carefully doubled back on the other side of the pipe. A 36" one would be good for a compressor, most likely.
|
|