Transformer question

Discussion in 'General Electronics Chat' started by rcullens, Jan 9, 2014.

  1. rcullens

    Thread Starter Member

    Apr 26, 2008
    15
    1
    Hell all,

    I pulled a mini transformer out of a circuit and looking at the schematic it has two legs on one side and three on the other. But the physical transformer itself has two legs on one side and four on the other. Can anyone tell me why that is?
     
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  2. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    Possibly to allow two secondary (or primary) windings to be connected in series or parallel.
     
  3. rcullens

    Thread Starter Member

    Apr 26, 2008
    15
    1
    Ok so how do I tell which one the schematic used? Also the "unused" fourth lead was soldered in the PCB but im not sure what it was going to.
     
  4. #12

    Expert

    Nov 30, 2010
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    By looking at the circuit board. There is no unused lead. Somewhere, two of the legs were connected together to make a center tapped secondary.
     
  5. JohnInTX

    Moderator

    Jun 26, 2012
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    Agreed. PREM and others make transformers with split primaries and secondaries so that various combinations of input/output can be handled. It sounds like your secondaries were stacked to make a center tapped transformer.

    BTW: PREM makes great stuff. First mfr. to come to mind.
     
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  6. huang

    New Member

    Jan 8, 2014
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    0
    help u to mark this thread ask some other engineer help u,sorry i am not engineer here,
     
  7. rcullens

    Thread Starter Member

    Apr 26, 2008
    15
    1
    Ok so which leg would i use? the schematic shows 3 and the transformer has 4?
     
  8. #12

    Expert

    Nov 30, 2010
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    Look at the circuit board and see which 2 pins were connected to each other. If you can't do that, you will have to give the primary some AC current and measure the secondary windings to find their ends and their phase relationship.
     
  9. rcullens

    Thread Starter Member

    Apr 26, 2008
    15
    1
    could I ohm it if i put it back in the circuit? or check voltage across it with power applied?
     
  10. #12

    Expert

    Nov 30, 2010
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    Ohms will do nothing for you. Voltage measurement is the only way.
     
  11. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    Can you post the schematic, showing the transformer connections?
     
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