Can i connect the ends of a transformer

Discussion in 'General Electronics Chat' started by Manmeyco, Jun 1, 2016.

  1. Manmeyco

    Thread Starter New Member

    Jun 1, 2016
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    [thread name should be "Can i connect the ends of a transformer"]

    If I connect the primary coil of a transformer to a regular (120v 60hz) outlet, what will happen if i connect the ends of the secondary coil together, with nothing else (making a complete closed loop)?
     
  2. Sensacell

    Well-Known Member

    Jun 19, 2012
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    Since you do not specify the type of transformer, I will make the assumption you are talking about a standard step-down power transformer.

    1) the magnetizing current in the "primary" (normally the secondary) with be high.
    The winding has fewer turns - less inductance, therefor greater magnetizing current.
    The inrush current may be high enough to blow fuses.

    2) shorting the "secondary" (normally the primary) will cause sparks - large uncontrolled current leading to destruction of something.
    You are basically shorting out the transformer.

    This is not a good idea.
     
    Last edited: Jun 1, 2016
  3. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    You will blow up your transformer!!
     
  4. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    BANG !!!

    Simon sez do not do this.
     
  5. RichardO

    Well-Known Member

    May 4, 2013
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    Not always. Some transformers are designed to allow for a shorted output. One example is a doorbell transformer.

    One UL requirement is that a transformer can not get to an unsafe high temperature after 4 hours with the secondary shorted. This can be accomplished several ways such as a thermal fuse built into the transformer, a transformer that limits maximum current by design or fuses in the power line or secondary windings.

    p.s. I have done the UL test on a small power transformer (a few VA ratinf) and it really does take hours for the transformer to reach maximum temperature. I was quite surprised.
     
  6. dl324

    Distinguished Member

    Mar 30, 2015
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    For one thing, you'll exceed the current rating of the secondary and likely damage the transformer. If you want to generate heat, there are better, safer methods.
     
  7. Manmeyco

    Thread Starter New Member

    Jun 1, 2016
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    So how can I measure the power output with a clamp ammeter - does it need a load?
     
  8. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    From what I remember of AC circuits, the theory goes, A purely inductive load draws no current in an AC circuit. In practice, the DC resistance of the load is still there so some heating will occur. I have not tried it myself but, according to theory, there will be no "boom" but heating should be fit any non-ideal inductor (I.e. DC resistance) power loss and heating.

    Good luck and be safe. Theory should be tested for your specific application with great care.
     
  9. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    Yes. It needs a load.

    You should measure the output voltage drop across the load as you test bigger and bigger loads. Current should be calculated from the known resistance of the load and the voltage drop across the load.
     
  10. crutschow

    Expert

    Mar 14, 2008
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    What inductive load? :confused:
    The OP is applying a short.
    The only inductance in the circuit limiting the current would be the leakage inductance, which is very small.
     
  11. crutschow

    Expert

    Mar 14, 2008
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    Are you trying to determine the maximum rated output power?
    That's not a straightforward test since a typical power transformer will output much more power with a low resistance load than it can safely continuously deliver.
    The easiest way to determine a transformer's power capability is to look at other transformers with a similar core size and note their power rating.
     
  12. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    Ok, I'm wrong.

    Here is a daring Russian experiment or showing the wrath of electrical power on a poor block if iron and copper to prove how wrong I am.

     
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