# Test transformer with signal generator and oscilliscope

I would like to see how well a sine wave would pass thru a transformer. (from primary side to secondary)

Is it possible/practical to test small transformers which you might find in small low powered consumer devices with a signal generator and an oscilliscope?

sample transformer:

https://www.hawkusa.com/manufacturers/hammond-mfg/power-products/pc-mount-transformers/161d120

if so, is it really just connecting the signal generator (sine wave) to the primary, and the oscilloscope to the secondary?

(assuming the windings ratio would not blow up anything)

• You probably want to connect a selection of different loads to the secondary as well (10k, 1k, 100R resistors for basic low power tests) in parallel with the scope probe. How a transformer works, with and without a load, are slightly different especially at high frequencies.
– user16324
Commented Feb 25, 2020 at 12:14

Yes, you can perform a basic test of a transformer by injecting a sine wave into one side and monitoring the other side.

Keep the frequency in the ballpark of what the transformer was designed for.

Pick a transformer that doesn't have a giant turns-ratio. Otherwise, if you stepping down, the voltage will be small and difficult to measure accurately.

If you use the transformer as a step-up, be careful. There probably isn't enough current to be dangerous, but you might get an unpleasant shock.

I would use a transformer with wires instead of terminals.

Note that this is only a basic test, you won't be testing many of the important parameters of the transformer (saturation current, ...)

Edit: I just tested a transformer that I have. It is rated: 115 VAC to 6.3 VAC, 4.8A.

With a function generator, 10 Vp-p in yields 0.668 Vp-p out. A ratio of 14.97.

Using the transformer ratings: 115/6.3 = 18.25.

Why the difference? The function generator test is unloaded. This is a good indication of the turns ratio. If I were to put 115 VAC into the transformer and load it with 4.8A, the ratio would be closer to 14.97.