[sdiy] Unmarked transformers

[TIm Daugard]

> ahh yes.  I was thinking "current transformer" or "Current Probe" and
oscilloscope.

And we're back to high cost. A Variac is cheaper than a current probe that can
give an accurate reading of a pulsed AC source

> Possible to use a series resistor (albelit a really high power one)

A light bulb. At lunch, I thought about putting a light bulb in series with the
transformer instead of in parallel. This would limit current for at least the
intial test.

> 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

I never connect my scope anywhere need line power - scopes are to hard to come
by. I only use meters with line power. When I was active in the Air Force, I
came back from lunch to the familiar smell of electronic smoke. A civilian
technian with a shortage of skill decided to determine which power cable was
carrying the 400 Hz 115 V power by using a frequency counter. PMEL (test
equipment calibration people) weren't sure they could repair the input amplifier
board.

> cannot
> estimate the saturation starting...

Then we get into the phase angle problem. A series resistor will give us a
voltage that is partially determined by the inductance.

A cheaper way to check a transformer might be to measure the inductance at 60 Hz
and then calculate power draw at line voltage level vs. core size. Charts for
the power capability of cores are fairly easy to find. However we rapidly
approach the point where the poor teenager starting out is totally lost.

BTW my favorite way to get a power supply is just go to the Goodwill Store and
look through their box of wall wart type power supplies. I occasionally find a
power supply with a cord attached that is marked +12V DC at some current rating.
I have found 12 Volt 2 Amp supplies for $1.00. With something like that, who
needs to worry about power supplies.

Of course, then the unmarked transformer, stripped out of equipment or found in
a flea market box of junk, gets tossed in my transformer bin, until it's time to
start this whole process over again.

 Tim Daugard
30.4078N 86.6227W