Needing help with power transformer

Discussion in 'The Projects Forum' started by innermuze, Sep 26, 2006.

  1. innermuze

    Thread Starter New Member

    Sep 26, 2006
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    I have an analog synthesizer that is set up for european voltage. The Transformer inside can be altered so that it can accept US voltage and Hertz. On this transformer there are four wires to which the line load will enter and the other side has a plug to where the voltage should be around +15v, -15v, and ground.

    I experimented slightly with the transformer to see what measurements I could with a small power supply. I measured across the +/- 15v/ground side aith a meter while applying voltage to the different wires on the other side. The colors of those wires are Black, Brown, Orange, and Yellow (in that order). The original wiing was sending the hot to orange and the nuetral to black. This was supposed to be set up for either 220v or 240v at 50Hz.

    Now while using a small load I tested different combinations of wires and found that the fuse blew when I connected the load to the orange and yellow wires. I figure this to be the hot for the 50hz load and the 60Hz load respectively. Therefore, I am left with the Brown and Black wires for the nuetral line.

    Since the Orange was the hot for the 50Hz, I should presume that the Yellow would be the hot for the 60Hz hot, correct? It just seems to make the most sense by the action of the fuse to me.

    Now if this is true, I found that with a 110v line load with hot to yellow and white/nuetral to the brown I got a reading of 17.2v and 10.37v when I applied the white to the black transformer wire. Would it be safe to assume that the correct wiring for an American line load would be the hot to yellow and the nuetral to brown at 17v? I know it is only a couple of volts over, but I want to be as sure as I can before making the wiring permanent and reconnection the power supply to the Korg synth.

    I appreciate any and all help!

    J
     
  2. kubeek

    AAC Fanatic!

    Sep 20, 2005
    4,587
    774
    Were the yellow and brown wires connected together for 220V? If yes, then it is double primary transformer.
    There are no windings made specially for 50 and 60Hz, there are only two windings for 120V, connected ins series for 220/240V, connected in parallel for 120V.

    To change it for 120V, I suggest you should measure first with an ohm-meter on disconnected device the resistance between the four wires. You should get two pairs showing conductance, black+something and orange+something.

    Then you leave hot on orange, neutral on black. You add the second end of the coil connected to black to the hot, and the fourth wire to neutral.
    This way it should be connected right.
     
  3. innermuze

    Thread Starter New Member

    Sep 26, 2006
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    Thanks for the reply!

    The yellow and brown wires were not connected to each other. Instead they were banded off to the side and covered so they could not touch anythig else.

    If this helps, the Transformer has KA-331 stamped on the top and also 100v 220v 240v 38v 14v

    I guess it would be so much easier if I could find someone with this particular synthesizer and just see what wires are right for use here. Until then, your info seems like it may be of help.

    Thanks again!

    J :)
     
  4. innermuze

    Thread Starter New Member

    Sep 26, 2006
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    I measured the wires and here are all the combinations...

    Black+Yellow = 134 ohms
    Black+Brown = 31 ohms
    Black+Orange = 119 ohms
    Orange+Yellow = 15 ohms
    Orange+Brown = 88 ohms
    Yellow+Brown = 103 ohms
     
  5. Gadget

    Distinguished Member

    Jan 10, 2006
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    I would expect the output voltage to be a little higher than +&- 15 volts, as there is bound to be a couple of regulators that need a couple of extra volts to work properly. Check the board for something like "7815 and 7915" 3 terminal regulators. If they have the 17 volts going in and 15 coming out, then all is well.
     
  6. kubeek

    AAC Fanatic!

    Sep 20, 2005
    4,587
    774
    So the resistances of the coils are 31-88-15 ohms.
    I would first try to connect it first to black - yellow, then to brown - orange and brown - yellow is the last possility.
    As you are trying those possibilities, measure the ac voltage at the secondary of the transformer and choose the option that is closest to the 14V value. If you can´t get reasonably near it, choose the higher one, but before this check the voltage capability of the smoothing caps, it should be at least 1.414 times higher than the AC voltage, but in practice at least 5V more than that number.
     
  7. innermuze

    Thread Starter New Member

    Sep 26, 2006
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    0
    Thanks a lot for all the help to both of you! I cannot express how grateful I am for all the help!

    After everything, I believe my initial thoughts may have been correct on which wires to use but it feels so good to have it confirmed in so many other ways.


    Just to show the details...

    When I applied the 110v load to the following color combinations, these are the values that I received... (N=Nuetral/H=Hot)

    Black (N) and Yellow (H) = 10.37v

    Brown (N) and Yellow (H) = 17.2v

    Black (N) and Orange (H) = 11.25v

    Brown (N) and Orange (H) = 19.94v


    The two best choices would then be either the Brown/Yellow and the Brown/Orange. I believe I feel comfortable with the Brown/Yellow unless there is something that I may be missing or if anyone feels that I should set it to the higher level just in case.

    I did look on the board and it has the 7915 as a regulator. I did not check the value at te 7915 as of yet, but I will shortly.

    Thanks again! :)
     
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