How to test a pulse transformer

Discussion in 'General Electronics Chat' started by Jotto, Dec 15, 2011.

  1. Jotto

    Thread Starter Member

    Apr 1, 2011
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    The easiest way to test a pulse transformer is using your oscope. The people with a Fluke scope that has three different cal tests is probably the best one to play with. Others will have the 1 or 5 volts cal that can be used. But all work equally as well as the other. I just like playing with more then one.

    Right now I am testing using a 1 vpp signal @ 1khz. You have to remove one of the terminals on the primary side to open the circuit. Apply your signal there and put the scope on the secondary. If you have amplification the transformer is good, if its flat or lower then the signal applied its bad. To get an idea of what a bad one looks like, put the cal on the secondary side and the scope on primary and you will get a idea what a bad one will look like. Also remember that you must disconnect the secondary if you wish to try that.

    vpp input .488 output 2.28
    acv input .172 output .808
    freq input 5khz output 13.1khz
    db input 13 dbm output .3 dbm

    I am using the scope on the primary and secondary. Notice the change in frequency from the 1khz being applied and then changing to 5khz on the input.
     
  2. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    What do you get on the output with different duty cycle input?
     
  3. Jotto

    Thread Starter Member

    Apr 1, 2011
    159
    17
    That would depend on the signal your using. This is just a quick test to determine that the transformer is good.

    Are you asking if your using a 5 vpp cal on the scope or using one of the extra ones that Fluke gives you? Or using a function generator. I can test the Fluke out tomorrow. I can take pictures also, but as I stated before the file size allowed here is too small for my pictures without cropping them.

    The smallest file size for me using my camera is 2mb. The only other option I can think of is making a pdf file.
     
  4. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    I've been interested in pulse transformers since I somehow got one and played with it.

    It acted really differently between 5% and 50% Duty, that's why I asked. I think I tossed mine away since I didn't know the full ratings.
     
  5. Jotto

    Thread Starter Member

    Apr 1, 2011
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    I did a few more tests at different frequencies. This is using the Fluke scopemeter.

    488hz
    vpp .208 input 16.72 output
    acv .07 input 5.90 output
    freq 1.32khz input 2.44khz output
    db -20.2 input 17.6 output

    976hz
    vpp .21 input 16.87 output
    acv .07 input 5.9 output
    freq 2.3khz input 4.88khz output
    db -20.3 input 17.7 output

    1.951khz
    vpp .22 input 16.8 output
    acv .08 input 5.92 output
    freq 3.6khz input 9.76 output
    db -19.7 input 17.6 output

    Sine wave
    vpp .06 input .11 output
    acv .02 input .04 output
    freq 102khz input 12.43khz
    db -30 input -26 output

    The only significant change is frequency, except on the sine wave which is not a good test for the transformer.
     
    Last edited: Dec 16, 2011
  6. jimkeith

    Active Member

    Oct 26, 2011
    539
    99
    There are numerous parameters that can be tested--each requires a different set-up:

    *V-us rating (when does it saturate?)
    *Leakage inductance (how tight is the coupling?)
    *Inter-winding capacitance (how well does it isolate?)
    *Turns ratio
    *Phasing
    *Winding resistances
    *Hipot voltage test

    Beyond that, there is voltage isolation rating that is inherent in the physical design
     
  7. Lundwall_Paul

    Member

    Oct 18, 2011
    220
    19
    The first thing that I do not see mentioned yet is the you need a copy of the specification for the part you want to test. Please post that if you have it.
     
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