how to power single phase induction motor?

Discussion in 'General Electronics Chat' started by aardbearst, Dec 10, 2009.

  1. aardbearst

    Thread Starter New Member

    Dec 10, 2009
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    I have a 120 VAC, 1.7A, 60 Hz induction motor that runs a very recently made European blower unit. The motor has an 8 mfd run capacitor and no centrifugal switch. There are 6 wires to the motor, black, white, yellow, green, blue, and red. There is a coil between the black and white wires, and another coil between the blue and white wires, apparently wound in the opposite sense. The cap is between the green and blue wires, and there is an internal connection between red and green (no resistance between these). There is a third coil between yellow and red. I think that the black/white coil is the 0 phase run coil, and the yellow/red coil is a phase shifted run coil. I'm not sure what the blue/white coil does, but it is probably part of the phase shift circuit.
    All coils have about the same resistance, 10 ohms, and the same inductance, about 15 mH.


    The question is simply how to hook this thing up to 120 VAC. I am tempted to hook line to black and yellow, and neutral to white, but I don't want to fry the unit. Diagram is here: (unit is a twin blower)


    http://i70.photobucket.com/albums/i105/smbird2/ScreenHunter_01Dec101804.gif


    All advice welcome! Thanks.
     
  2. BillB3857

    Senior Member

    Feb 28, 2009
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    348
    From the looks of your drawing, the box at upper right is the start relay. It is activated when power is applied and supplies power to the start winding until the current drawn by the combined motors drops to a preset value. If I were a betting person, I would bet that there is a screw sticking out of the box somewhere with a paint seal on it. That is how the dropout current is adjusted.
     
  3. aardbearst

    Thread Starter New Member

    Dec 10, 2009
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    Bill,

    Thanks for this; you are very likely right about the start relay, though I don't have any hardware upstream from the terminal block. I'll have to obtain a proper start relay, and insert it between yellow and black.

    Do you think it likely that the three coils are two run coils and one start coil, where the two run coils can be series (240 VAC) or parallel (120 VAC)? That's my guess.
     
  4. BillB3857

    Senior Member

    Feb 28, 2009
    2,400
    348
    After looking at your drawing again, could the box I thought was a relay actually be a speed switch? Do you have the original fan to check? I may have jumped the gun on this one.
     
  5. aardbearst

    Thread Starter New Member

    Dec 10, 2009
    4
    0
    Bill,

    Thanks again! What I have is the two fan blower unit with a cable that comes
    to a connector that is wired to the main terminal block. The other items on the diagram did not come with the unit.

    I did check to see whether the motors would turn if only the white-black coil was energized, or if only the blue-white coil was energized, and the motors
    were spun by hand. No joy.

    If your original guess was correct, then I guess one would connect the two run coils in parallel, and the cap-coil-relay circuit in parallel with those coils. As it happens, I have a timing relay, so I could hook it up. However, since the motors do not turn when hand spun, I'm not very sure about this topology.

    What do you think?
     
  6. BillB3857

    Senior Member

    Feb 28, 2009
    2,400
    348
    Without knowing exactly what is inside the box, it is really hard to say. Since it is a fan, it would make sense that it would have multiple speeds. One set of windings for high, one for low and the other with the cap for direction.
     
  7. aardbearst

    Thread Starter New Member

    Dec 10, 2009
    4
    0
    Bill,

    Thanks once more. I'll just try some more experiments, say by powering both of the run coils, and the start coil; it seems that I'm not going to fry the unit if
    I only power for a few seconds.
     
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