I constructed a rotary phase converter from a 5 HP motor. The converter converts 220 single phase to 240 3 phase. Well, it is supposed to. I am getting some very odd results that I am wondering if someone can help explain.

I wired up the circuit exactly how is done below: enter image description here

I used a ~420 uF starting capacitor and it works just fine starting up. However, the legs are out of phase when it is running. The weird part is, even if I remove the run cap completely, it is STILL out of phase! I had 3 caps on hand, a 15uF, 30uF, and 50uF. So I did some experiments and I am getting confusing results. Here are the voltages between the wires: enter image description here

So there doesn't appear to be a capacitance value I can choose to get all of the legs in phase. Furthermore, why is it that the legs are out of phase with NO run capacitor? Is the back emf from the potential relay causing an unintentional phase shift???

  • \$\begingroup\$ I thought a rotary phase converter was essentially a motor driving a generator. You seem to be trying to use a single-phase induction motor as a phase converter by itself. Am I just ignorant, or is what you are trying to do kind of sketchy/impossible? At best, I would think this arrangement would be VERY load dependent. \$\endgroup\$ – mkeith Mar 24 '17 at 3:22
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    \$\begingroup\$ I may be using the wrong terminology, but this kind of thing is done very frequently by machinists wanting to run 3 phase machines on single phase power (which is the reason I want to do it too). From what I can find, many many people have claimed to have done this successfully and have had it work for years. That doesn't mean it isn't load dependent though. I am sure the legs go out of phase a bit when under heavy load, but apparently it isn't enough to cause obvious harm. \$\endgroup\$ – user41178 Mar 24 '17 at 3:27
  • \$\begingroup\$ I was thinking that it may only work properly when the load is connected. The load, being a three-phase motor, would be reactive, too, and may affect the balance. Anyway, I will bow out since I can't help. Watching with interest. \$\endgroup\$ – mkeith Mar 24 '17 at 3:31
  • \$\begingroup\$ Maybe just clarify one point. The 5 HP motor. Is it a three-phase motor, or a capacitor run, capacitor start single phase motor as shown in the schematic? And if the latter, where are you taking your three-phase power from? The videos I found on youtube all showed a three phase motor being used to create three phase power. \$\endgroup\$ – mkeith Mar 24 '17 at 6:04
  • \$\begingroup\$ Yes the motor is a 3 phase motor. Two of the phases come from L1 and L2, and the third one comes from one of these lines but is phase shifted by the starting cap. I will be taking 3 phase power from the motor itself after it has been started, as once it is running, it generates the third leg. (At least according to my knowledge) \$\endgroup\$ – user41178 Mar 24 '17 at 12:34

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