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Single phase motors with 3 wires into motor HElP

  1. Jul 13, 2012 #1

    I was wondering if anyone could help me, I have a single phase motor with a single capacitor,on a woodworking saw, which the switch broke, it was sprung loaded, so I guess a start run switch. It's for a friend and he took the switch off without marking the terminals, I can't find another switch like it anywhere, I have tried making my own start switch using a n/o push button, but I keep blowing fuses there are three wires going in a black brown blue, the blue is connected to a thin brown wire going straight into the motor, the brown is connected to capacitor a thicker red wire, the black goes to another black wire and also a thinner brown, if anyone can help it would make me so happy!

    Thanks scotty
  2. jcsd
  3. Jul 14, 2012 #2
    Here is a picture if anyone can help! thanks

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  4. Jul 14, 2012 #3

    jim hardy

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    is that photo looking at the old broken switch?

    here's a washing machine motor i recently decoded with an ohm-meter.


    Yours will be similar but with no "slow" winding. What i called "fast" is the run winding for you. Sadly there seems no systematic color code.

    Start winding will be a few ohms, run winding will be fewer.

    Isolate start winding.
    Apply voltage across run winding and motor will hum but not start.
    Give shaft a spin either direction and it'll run that way.
    It won't hurt the motor to hum a few seconds but dont let it go on long.
    That'll tell you whether the motor is going to be useable.

    We'll go from there.

    old jim
  5. Jul 14, 2012 #4
    Am I right in saying the neutral will be connected to the negative of the capacitor? Thanks very much for replying really appreciate it, it has become a personel how to myself to get it working again! Thanks again scott
  6. Jul 14, 2012 #5


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    A capacitor for AC use doesn't have a "negative" terminal as the volts alternate as much one way as the other. There may be an 'earthy' side , though, and that is sometimes indicated on the case. That would be connected to the neutral.
  7. Jul 14, 2012 #6
    Ah ok right, I was told find the negative of the capacitor and that would indicate where my neutral of the incoming poeer to the motor would be.
  8. Jul 14, 2012 #7


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    I think that was 'shorthand' for "Earthy end".
    Point is, can you actually identify the right terminal?
  9. Jul 14, 2012 #8

    jim hardy

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    do those wires disappear into the motor or are those the three wires from spring loaded switch?

    i can't tell which is which in your picture.
    is the capacitor shown in your picture or is it external?
    Does it have a value stamped on it?

    What are those brown and blue wires coming in upper left, the ones that somebody added after the top was removed?

    Do you have a multimeter with ohms scale on it? RX1 would be best, or a digital.

    I couldn't decipher this phrase
    by a thicker red wire perhaps?
    and a thicker red wire perhaps?

    perhaps you could use PAINT or something and annotate the picture.

    Here's my best guess at what you have.


    The print came out a bit small

    as you see i made some assumptions about the capacitor
    see if this works

    [apply power between center and rightmost terminals
    measure voltage between leftmost and center
    if motor starts you should read voltage there only after motor has reached speed.]

    if it works my assumptions were good.
    If they were and those two mystery wires are how you applied power, you put it across the centrifugal start switch and may have burnt its contacts. But it'd explain blowing fuse.

    I too feel obliged to rescue old machines. it's usually an iterative process, though .

    Good thing i can't afford an airplane. I Love old Bonanzas but they are a money pit..

    old jim
  10. Jul 16, 2012 #9
    hey i have revised the drawing to show what the parts are, hope this clears it up a little? im still unsure why i would have 2 lives coming from a signle phase supply, i have never seen this before, it would beeen soo bloody good if there was a drawing on the inderside of the plate! it must be the few ive seen withouht this! thanks for help again!


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  11. Jul 16, 2012 #10

    jim hardy

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    that's some help but i too find one too many wires. And i still can't see whether they land on the three terminals or disappear into motor's innards.

    next is it blowing fuses in this configuration?

    How'd it get in this configuration, in other words are we looking for external wiring trouble or internal motor trouble?

    Are you sure there's no brushes in the motor?

    Have you a multimeter?
  12. Jul 16, 2012 #11
    That's how the motor was wired in this configuration it worked, so definitely external problems, so its the configuration of the external, yeah I'm pretty sure there's no brushes,

  13. Jul 21, 2012 #12

    jim hardy

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    perhaps we need to look at the switch, then.

    Have you a photo of it?
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