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Transformer wiring

Discussion in 'Power Electronics' started by zii000, Sep 22, 2021.

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  1. zii000


    Sep 22, 2021
    Hi, I have a question about the polarity of secondary windings on a step down transformer.
    Both secondaries are 15v but my circuit needs 15-0-15 so I'm assuming I can just connect in series to emulate a centre-tapped winding. Does it matter which end of the secondaries are connected together for the zero connection? I realise this is elementary stuff but I'm lacking a bit of knowledge and understanding. Because this is AC there's no polarity so I just have four colour-coded wires for the two pairs of 15v but no indication of how these relate to the actual physical windings laid out on the secondary core. Does this matter or can I just connect together any way round ? Thanks for any help.
  2. dave9


    Mar 5, 2017
    You cannot connect together any way around, because the phase will be reversed if hooked up backwards so they would cancel each other out.

    See if you can find the datasheet for it, or look at which direction each lead is wound around the core. If one winding lead is going clockwise around the core and the other (of same winding) lead counter-clockwise, you'd connect the clockwise to the counter-clockwise of the other winding.

    If you don't yet know which two are pairs for each winding, measure for resistance as there will be none if they aren't the same winding (with none connected together by you yet).
    Last edited: Sep 22, 2021
  3. bertus

    bertus Moderator

    Nov 8, 2019

    You will need to watch the phase of the two coils.
    This image from the ILP transformer datasheet shows a dot for the start of the coils:
    Keep in mind that the colors apply for the ILP transformers.
    Try to get a datasheet for your transformer to get the correct connections.

    Some transformers do have the 0V indicated (start of the coil) .

    Also a picture may help.


    Attached Files:

    Harald Kapp likes this.
  4. Minder


    Apr 24, 2015
    Connect the transformer with the two secondaries in series, test outer ends, it will be either zero or when correct, 30vac
  5. zii000


    Sep 22, 2021
    I get it now (finally), thanks for the help, much appreciated.
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