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connecting 2 transformers

Discussion in 'General Electronics Discussion' started by polyal, Sep 17, 2011.

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  1. polyal

    polyal

    12
    0
    Sep 8, 2011
    i have two identical transformers 240v / 21v sec
    can they be configured to give me 21-0-21
    regards
    polyal
     
  2. davelectronic

    davelectronic

    1,087
    12
    Dec 13, 2010
    Transformer in series

    Hi polyal.
    I am not 100% sure as ive not done it before, i did read some where if there in phase it will work, i am not sure putting them in series and using a meter to see, then maybe reconfigure if not, try that, personally i dont see the point, ok for series connection or parallel. Somethings telling me its no, but i might be wrong, iam a hobbyist, ive used single series and parallel but not tried what your asking. Dave. :)
     
  3. Resqueline

    Resqueline

    2,848
    2
    Jul 31, 2009
    Sure, it can be done. Being identical their phasing should be the same. Primaries in parallel and secondaries in series.
     
  4. davelectronic

    davelectronic

    1,087
    12
    Dec 13, 2010
    transformers in series

    Hi Resqueline.
    So the center of the series connection can be used at 0 volts AC for a center tap rectification, if yes that answers my own not completely being sure. Dave. :)
     
  5. daddles

    daddles

    443
    3
    Jun 10, 2011
    Cut the top of the transformers off (in your mind, of course :)), extend the central core (I'm assuming an E core) and drop the windings of the other transformer on the core. Then replace the top you cut off. Excluding saturation issues, the two cores should now behave like a center-tapped transformer, as long as the windings' phases are the same. At least that's my mental model...
     
  6. Resqueline

    Resqueline

    2,848
    2
    Jul 31, 2009
    Yes, you wire them just like you would DC supplies, and you get twice the VA rating of each. Of course you also need to pay attention to the primary polarity.
     

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  7. davelectronic

    davelectronic

    1,087
    12
    Dec 13, 2010
    Centre tap transformer

    That answers the op for me, and handy to know, ive a couple of low VA transformers in the cupboard, it adds more options, thanks to you both for your input. Dave.
     
  8. polyal

    polyal

    12
    0
    Sep 8, 2011
    thanks for the replies.....i suppose if the primaries were wired in series
    it would become a 10.5v - 0 - 10.5v since there would be 120v across
    each primary ( and a combined VA )

    polyal
     
  9. Resqueline

    Resqueline

    2,848
    2
    Jul 31, 2009
    Yep, that's right (and the total VA rating would be the same as for one - since the voltage is halved but the allowable current stays the same).
     
  10. duke37

    duke37

    5,364
    772
    Jan 9, 2011
    Two transformers instead of one has the disadvantage that if they are to feed a diode rectifier, there will be a net DC current in the transformer giving the possibility of core saturation.
    If you want a +/- DC supply you might be better using a bridge rectifier on each transformer and then putting these in series.
     
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