[sdiy] Unmarked transformers

[harrybissell]

TIm Daugard wrote:  <snip>

> Yes it can - it puts out spikes of current at 60 Hz. The theory is that the
> spikes have higher frequency harmonics the the orginal power frequency. Higher
> frequencies are less dangerous for the transformer than lower frequencies -
> higher frequencies require less metal in a transformer. Thats why the military
> use 400 Hz for aircraft.
>
> Inductance = 2*PI*F*L

The higher harmonics have little energy and there is no danger there. The danger is
asymmetrical firing of the dimmer, a real possibility of putting DC into the primary

windings.

> How? If you are using a meter it's looking for a sine wave current profile. I
> don't think that monitoring the output current of a dimmer would give any kind
> of accuracy. I monitor the transformer voltage on the leads that I hope are a
> secondary. I generally lightly load the secondary with a 100K resistor. (Forgot
> to list that, sorry.)

ahh yes.  I was thinking "current transformer" or "Current Probe" and oscilloscope.
Possible to use a series resistor (albelit a really high power one) and a TRUE
DIFFERENTIAL scope probe... none of this pseudo-differential crap.  I never ever
connect a scope ground to either side of the AC line.  Without one of these you
cannot
estimate the saturation starting...

> I don't fuse when I'm testing the transformer. If I thought it was a power
> transformer and it's not, it's either going to be disassembled or thrown in the
> trash. I rely on - circuit breaker in my workshop, very little current through
> the dimmer to start (doesn't always work - some time the breaker trips), and a
> quick hand on the dimmer located at least 4 to 5 feet from the transformer under
> test (don't forget the clear plastic panel to deflect any blast damage.)

Yes that would work... and large guage wire so you don't fry the lamp cord as well.

H^) harry