Vintage 50's Japanese induction coil, secondary coil repair help

Discussion in 'General Electronics Chat' started by texasdave, Jul 22, 2013.

  1. texasdave

    Thread Starter New Member

    Mar 22, 2011
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    Hey all,

    Long time listener, first time caller:

    I've come across a 50's era made in Japan induction coil that was used in a lab setting. It is so beautiful I would like to repair it. Here is what I THINK is the problem although I could be totally wrong:

    BAD - The secondary shows no continuity, which I'm assuming means there is a disconnect in that portion of the coil.

    GOOD - The primary shows continuity throughout as expected, from the contact breakers to and through it.

    WEIRD - The low voltage inputs do not show continuity, I thought the low voltage inputs went into the primary, they certainly look like they do. Is there some sort of center tap thing going on?

    The capacitor is new and good.

    Any tips on repairing a secondary coil, or should I just make a new one?

    thanks in advance for any help.

    dave
     
  2. t_n_k

    AAC Fanatic!

    Mar 6, 2009
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    Be careful - insulating oils from that era could now be considered carcinogenic.
     
  3. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    It might be wound like an automotive coil (auto transformer). Three leads where one common connects two coils. Similar to a variac but for a different purpose.
     
  4. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    Very good point, poly-chlorinated biphenyls (the wrong kind of PCB).
     
  5. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    After sitting on your story overnight, I am thinking the secondary may appear to be shorted out because the secondary is in series with the spark plug gap. It will only conduct at high voltage.

    Try shorting out your spark plugs and then testing continuity of the secondary again.
     
  6. shortbus

    AAC Fanatic!

    Sep 30, 2009
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    Quote "WEIRD - The low voltage inputs do not show continuity, I thought the low voltage inputs went into the primary, they certainly look like they do. Is there some sort of center tap thing going on? "

    The primary will only show continuity on the inputs when the breaker points are closed.
     
  7. shortbus

    AAC Fanatic!

    Sep 30, 2009
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    Automotive coils are like this because they share the vehicle ground. Both the primary and the spark plugs share the vehicle ground/common. They aren't a true "autotransformer". Even though they are a transformer in an auto.:D
     
  8. MaxHeadRoom

    Expert

    Jul 18, 2013
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    What is the reasoning there?
    Max.
     
  9. shortbus

    AAC Fanatic!

    Sep 30, 2009
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    Well an autotransformer only has one winding, like a Variac.

    An ignition coil is a transformer that exists in an automobile.

    And the ignition coil has two windings, a primary and secondary.
     
  10. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Well all the old Delco-Remy coils I have used in experiments have three terminals.
    + & - and H.V.. the common end of the H.V. connected to -ve.
    Auto transformer mode?
    Case is isolated.
    Max.
     
  11. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    Some automotive windings of yore had only one winding as well. They are normally shown as two windings on a schematic (as below) but were one winding with an off-center tap. Note the comment in the image, "internal connection" so the user does not look for the second coil.

    [​IMG]
     
  12. shortbus

    AAC Fanatic!

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    Wow, that's really old. Must also be 6V positive ground too. That also shows what I'm saying, the secondary and primary SHARE the ground. Even the coils on a lawnmower are made that way.

    If you ever took apart a coil you would see what I mean. I've taken apart many of them for the wire when I was a younger guy, 6V an 12V. They all had two different gauge wires in them, a larger gauge, shorter length primary and a smaller gauge longer length secondary. Had all different makes and models to work with, all the same inside.
     
  13. texasdave

    Thread Starter New Member

    Mar 22, 2011
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    Wow thank you all so much for the help, this gives me a lot more confidence to test / repair this tiny piece of history. I'll have an update as soon as I can.

    thanks again!

    dave
     
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