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I burn wood and salvaged an old 1/20 hp 1550 rpm two speed GE single phase motor (5KSM59CS12K6AS if anyone can find more info, curious what speeds are). I'm trying to make a digital fan controller that will kick onto low as stove heats up, high while hot, and then step back down.

I found some pretty slick (from my limited knowledge of chinese) dual relay controllers Inkbird ITC-2000 that has 10A hot/cold and an alarm relay. I'm not sure that it shuts off the temperature relay when the alarm relay is powered. Ie low and high would be simultaneously powered.

What I'm wondering is how exactly is the speed decided on this motor (three wires)? Right now I'm running the stove the stove on wire nuts choosing which coil/speed to power, but the other day I powered the black AND red wire and nothing blew up and the speed remained unchanged on high. I'm just looking for a some sort of confirmation that I won't burn up the motor or some knowledgeable person telling me I'll eventually burn it up as motor is fighting itself.

Thanks in advance

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I suspect that the motor is the shaded pole type. If it is, there is only one coil of wire that is connected to power. There is also a short loop of wire that has the ends shorted together. That loop goes around a small section of the steel laminations. The speed is probably changed by applying voltage to either the entire coil for low speed or to only a portion of the coil for high speed. When voltage is applied to both the black and red wires, current flows through only part of the coil. The unused part of the coil is shorted rather than disconnected. It is unused either way. One or two good close-up pictures would help to confirm what you have.

It is likely that the last few characters of the part number identify variations of the motor while the first characters identify the basic design. If you search using fewer characters you might find useful information for a similar motor.

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  • \$\begingroup\$ I think it must be as I described. If you could measure current of high speed with and without the low speed wire also connected, that would pretty well confirm it is ok to make that connection. You could also check the temperature of the housing. \$\endgroup\$ – Charles Cowie Oct 26 '16 at 1:42
  • \$\begingroup\$ Upon further consideration, it occurred to me that the unused part of the winding would act like an autotransformer secondary winding with the used part being the primary. That would cause some circulating current produced in the unused part of the winding and the short-circuit connection with the red and black wires connected together. The circulating current may or may not be high enough to cause excessive heating. You should measure the current to make sure it doesn't exceed the normal operating current. It would be better to avoid that mode of operation. \$\endgroup\$ – Charles Cowie Oct 26 '16 at 3:07
  • \$\begingroup\$ OK I borrowed a cheap multimeter from work. It couldn't measure that high of amp load, but I could measure the resistance. Low measured 50ohms exactly, high was 26.1, and the shocker was resistance between high/low together and neutral was 26.1 ohms. Correct me if I'm wrong here, but I think this is good news as I can power both relays simultaneously. I was doodling a wiring diagram and I think I could put in a spdt relay to cut power to the low when high engages...but it's more complexity and another point of failure. \$\endgroup\$ – Schmitey Oct 28 '16 at 1:22
  • \$\begingroup\$ While the motor is running with the high connected, measure the voltage between high and low. What is the supply voltage? \$\endgroup\$ – Charles Cowie Oct 28 '16 at 3:09
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If black wire is hot it is full speed, if red wire is hot it's low (or vice versa I don't remember). I originally cut it off a two way switch. Still not sure what happens when both wires are powered, I suspect nothing that doesn't happen normally unseen.

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