Transformer repairs

der Mouse mouse at Rodents.Montreal.QC.CA
Sat May 31 21:33:09 CDT 2008


>> It is probably possible to build a current limiter that provides
>> immediate visual feedback.  I challenge you, or anyone for that
>> matter, to come up with such a design that is as cheap, easy,
>> simple, and foolproof as an incandescent bulb.
> How's this?  Grab a glass jar, fill with water and a salt of your
> choice, say, bicarbonate of soda, drop two electrodes into it
> (stainless steel or carbon is good; aluminum will tend to polarize
> after awhile and form a leaky rectifier).  Apply current and watch
> for bubbles and/or steam.  Vary resistance by varying the distance
> between electrodes.

Ingenious.

However, it tends to produce an explosive atmosphere.  It also is
substantially slower to produce visual feedback, and requires looking
fairly directly at it to see the feedback (which is true of
incandescents only for the low end of the current range).

> What I don't like about incandescents used as a load-limiter is the
> very low cold resistance.  I'd much rather have a "soft" start--but
> then carbon-filament incandescents haven't been easy to find for the
> last 80 years or so.

If you don't like the cold inrush, maybe you should get that 144 ohm
100 watt resistor I mentioned...and parallel it with some kind of
voltmeter, maybe as simple as a diode bridge, resistor and meter
movement.

Seems to me that, at least for power supply applications, a cold inrush
is actually a good thing, since it gets the smoothing caps up to
voltage faster - and doesn't last long.

					der Mouse



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