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dual voltage motor issue

Discussion in 'Compressors, Boosters and Blending Systems' started by rjack321, May 22, 2020.

  1. rjack321

    rjack321 ScubaBoard Supporter ScubaBoard Supporter

    # of Dives: 1,000 - 2,499
    Location: Port Orchard, WA
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    So I picked up another shop compressor to run my booster. I has a 3hp 120/240V motor on it. Unfortunately the wiring sticker is worn away so I can't tell if it's jumpered for 120v or jumpered for 240v. The 4 terminals are not labelled at all. How can I tell these apart with a multimeter?

    (it has 2 capacitors on top if it matters)

    100042830_324518535199589_3796239584828850176_n.jpg
     
  2. BRT

    BRT ScubaBoard Supporter ScubaBoard Supporter

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    I don't know if I can get you all the way but I believe #1 and #2 are 1 winding and #3 and #4 are the other winding. With no jumpers you should get continuity from 1 to 2 and from 3 to 4. Connecting #1 to #3 and #2 to #4 puts the windings in parallel, connecting the power to #1 and #4 and the jumper between #2 and #3 puts the windings in series for the high voltage. Kind of like this
    #1-WINDING -#2 #3-WINDING-#4

    One jumper in place would be on 2 and 3, two jumpers in place would be from 1 to 3 and from 2 to 4. If it has one jumper it is set up for high voltage, 2 jumpers and it is set up for low voltage.

    It is almost certainly wired for 240 because it would require a large breaker and large wire to run it on 120 volt.
     
  3. rjack321

    rjack321 ScubaBoard Supporter ScubaBoard Supporter

    # of Dives: 1,000 - 2,499
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    I won it in an auction. There's no power wires on the motor at all (and the pressure switch is unpowered). There do seem to be jumpers coming off two of the 4 terminals inside the motor case, but they route inside and I can't tell where they go.
     
  4. BRT

    BRT ScubaBoard Supporter ScubaBoard Supporter

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    Pictures of that might help. Lots of different ways to do 1 phase motors.
     
  5. BRT

    BRT ScubaBoard Supporter ScubaBoard Supporter

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    Pictures of the motor nameplate might help too.
     
  6. iain/hsm

    iain/hsm Manta Ray

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    It's a typical American wiring logic diagragm, a thing of mysticism that defies logic.
    Most electricians conect any wire until it stops emmiting sparks or runs in the correct rotation.

    Failing that the British contingent on here would look at the wires inside to see if they have numbers printed on them
    Then for a 240 Volt supply single phase, wire No 1 is live and wire No4 is the neutral.
    The remaining wires No 3 and No2 are connected together.

    Photo enclosed below of one I built earlier with the added complication of being wound for both 50 and 60 Hz as well as the usual 110V or 230 volt

    IMG_1828.jpg
     
  7. Wookie

    Wookie Secret Field Agent ScubaBoard Business Sponsor

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    And the 2 capacitors probably indicate a reversing motor...
     
    iain/hsm likes this.
  8. iain/hsm

    iain/hsm Manta Ray

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    The motor data plate with the wire colours or numbers together with the wire hook up drawing you have is all you need. Edit photo enclosed to fully show reverse rotation winding option

    IMG_1093.jpg IMG_1649.jpg
     
  9. broncobowsher

    broncobowsher Solo Diver

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    2 Caps are a good sign. It is a capacitor start/capacitor run motor. More efficient. Nothing to do with reversing.

    How is it wired? Real easy. Count the number of jumpers.
    If 2 jumpers are present (or 2 wires are spliced together twice) it is 120V. That is 1+3 together and get power, 2+4 get neutral
    If there is one jumper (or a single splice present) and two single wires out in the open, 220V That is 2+3 are spliced together and buried in the junction box, 1+4 are dangling in the breeze.

    This is only true for the data plate presented in the 1st post.

    Now if someone went in and took all the splices out, and all you have are 4 wires hanging out in the breeze, no telling how it was wired before as it is not relevant.

    Another tip, look at the picture in the 6th post. There are numbers printed on the wire insulation. That is fairly common. That will also help.
     
  10. Wookie

    Wookie Secret Field Agent ScubaBoard Business Sponsor

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    Every one of my 2 capacitor 240v single phase motors are reversing, and one capacitor starts the motor in one direction, and one starts the motor in the other direction. I am busy swapping them for 3 phase motors, and I am not the all knowing motor guru, but the only cap start cap run motor I have does not have the capacitors mounted to the motor, they are in the motor controller, and the caps are very different.

    Again, I am well versed in 3 phase squirrel cage motors, but all of my 2 cap motors that have the caps mounted on the motor are reversing.
     

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