# How to test center-tap transformer?

1. ## How to test center-tap transformer?

hello everyone:
There are only function generator and digital CRO for tseting the transformer. I have problems on ways of connections and input signal for testing on center- tap one. Pl give some suggestions to me...

Best regards

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2. ## Re: How to test center-tap transformer?

Hi Helenwell,

Connect your generator to the primary of the transformer and the scope to the center tapped secundary. Choose one of the three connections and connect
both ground clips to this connection and measure both remaining connections
with both scope channels and observe both outputs.
There are two possibilities:

1. Both signals have the same amplitude but are opposite in phase, the
connection you chose to connect your ground clips to is the center tap.
2. Both signals are in phase, but one connection has the double amplitude of
the other, your ground clips are attached to one of the extremities of the
secundary and the one with the largest amplitude is the other extremity.

Regards,

on1aag.

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3. ## Re: How to test center-tap transformer?

thanks on1aag:
The problem for me is my primary side of the transformer is center-tap, which is 12V-0-12V, secondary side of the transformer is 220V. So i dunno how to give the input signal to the transformer:(

regards

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4. ## Re: How to test center-tap transformer?

Plug it (with necessary precautions) to a wall socket... you'll
get your 220 / 110V there. Then measure the secondary
voltage...

5. ## Re: How to test center-tap transformer?

Hi Helenwell,

Switch your function generator to sinewave and adjust it to the line
frequency. Set the output voltage at 1 volt. Connect it to your
transformer, any way you like and measure the opposite side of
your transformer. If the output signal is about nine times larger than
the input signal, you're measuring at the primary side of your transformer.
If the output signal is about nine times smaller than the input signal,
you're measuring at the secundary of your transformer. You don't
have to be afraid to perform this measurement, you won't damage your
transformer or your scope, it's absolutely safe.

Regards,

on1aag.

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6. ## Re: How to test center-tap transformer?

Hi Helenwell,

Yours appears to be a power transformer. Just connect the 220v side to the mains power through a fuse (preferabaly). Measure the 12 v between centre tap and one winding. Do the same with centre tap and other winding. You should get 12 v each. Now measure the two windings (end leads). You should get 24V. This is correct configuration. If end to end measures 0 or few volts ( instead fo 24V), the one of the phase is reserved. Invert any one winding (make end as centre tap and centre tap as end). You should now get 24V fron end to end.

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