Mike Hawkshaw <mike@spikey-mike.com> wrote:
> If you look at the output on an oscilloscope you will see a sin wave.
> Even if you overload the electrical limits by taking too much current
> through the windings you will see a sin wave. If you overload the
> magnetic circuit it will saturate and the tops of the sin wave will
> start to sqaure off.

Another way to check this (that's a bit more sensitive) is to monitor the
primary current by inserting a small-value series resistor. Put the 'scope
across this, and drive the unloaded transformer from a variac, especially
if there's any doubt about whether it's a 110V or 220V primary. If the
magnetic core saturates as you're turning up the voltage, you will begin
to see some serious spiking at the peaks of the current waveform.
You'll definitely see magnetic saturation if you try to drive a 110V
transformer with 220V.

You might also measure the magnitude of the magnetizing current (prior to
saturation). From this, you can calculate the primary inductance. You can
also try to make a judgment as to whether the wire gauge is sufficient to
carry the magnetizing current without excessive heating. Or, as Mike said,
just let it run for a while and see how warm it gets.

-- Dave Tweed
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