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Start capacitors on 2 phase equipment

  1. Aug 1, 2014 #1
    Hi there. So here goes.

    I have been having issues with a replacement chiller unit that requires 230VAC single phase.
    An identical unit was running on 2 phases of a 110VAC 3 phase supply. I had a start capactior fail in this unit. When I connected the replacement unit, the compressor failed to kick on however it started when bumped with my fist. After kicking off however, the compressor would not always kick back on when required.

    So..... Since the power supply I'm using to "mimic" a single phase 230VAC supply is ACTUALLY a 2 phase 110VAC (2 of 3 phases) ie. not 180° opposed but 120° then 240°, does this mean that with regard to starting capacitors, polarity becomes an issue?

    I am aware that the resultant voltage is 208VAC, however the original unit has run on this supply for a number of years without issue.

    Thanks for any insight.

  2. jcsd
  3. Aug 1, 2014 #2


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    Science Advisor

    The starter capacitor with the new motor may be insufficient to pass the necessary starting current at the lower voltage.

    Induction motors do not like low voltages, as they then draw a high current.
    The starter capacitor has less voltage and a higher current demand. It will be too small.

    New motors are built closer to the minimum spec. Old motors are more tolerant to abuse.
  4. Aug 1, 2014 #3

    jim hardy

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    Gold Member

    Are there two or three power wires going into the motor ?

    A 208/120 system
    is 120 single phase when connect from phase to neutral
    and when you connect with just two wires from phase to phase it's 208 but still single phase

    so your assumption about phase angle
    is not correct unless all three phases, not just two of them, are carried to the motor.

    Draw your phasor triangle.

    Baluncore seems on right track. A bigger start capacitor may help. Electrical supply houses sell "hard start" kits for residential airconditioners - basically just more starting capacitance.
  5. Aug 7, 2014 #4
    Thanks guys. I appreciate the input.
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