RPC produced voltage
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  1. #1
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    Default RPC produced voltage

    The roto phase i have produces 240v, the other two lines are 120v from my service. Is it producing to much? I got 2 buck boost transformers to buck it to 208 because of my 200v motor. I did realize that one leg was producing 240v. when i turned it on going through transformer it read one leg read 208v and other 84v then i shut it down worry that i would fry something. any suggestions?

  2. #2
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    You are measusring the voltage to ground and that tells you very little for a 240 volt system. Measure the voltage from phase to phase and see what it is. You should find it is something near 240 volts on all three phases without the transformers. A closed delta 3 phase system has a "wild leg" which will measure about 208 volts to ground while the other two will measure about 120 volts to ground. A RPC produces a closed delta 3 phase output and this is all you measured. It is what one would expect to find and is the way to find the "generated or wild leg". The RPC genereated leg is a higher voltage than true 3 phase closed delta due to the capacitors used in the RPC.

    Here is a hypothetical solution to your problem as I do not know the real output voltages until you measure them.
    T1 to T2 = 240 volts (you single phase line voltage)
    T1 to T3 = one generated phase (should be a little higher than your single phase line) maybe 260 volts
    T2 to T3 = the other generated phase (should be a little higher than your single phase line) maybe 250 volts.

    all three phases will need to be reduced about 32 volts.

  3. #3
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    Thanks for the reply. I got my transformer producing what it needed to, I put the wild leg on the wires that tied the two transformer together. Voltage is within 10% of tolarence. Lathe runs smooth and cool. It just Throwed me off, that high voltage, I see how it works now.


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