In article ,
John Fields wrote:
On Mon, 10 Feb 2014 00:11:40 -0800, Kevin McMurtrie
wrote:
In article ,
John Fields wrote:
begin 644 Hand calcs0003.pdf
LOL! Isn't that one of the early "150 in one" finger shocker circuits
that didn't work.
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Dunno, but I've gotten hit with HV off the secondary when a few
volts across the primary was disconnected.
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The transformer saturates before the relay engages.
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That depends on the transformer's primary's inductance, the
transformer's saturation current, and the relay's actuation time.
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If the 1.5V battery
can overcome the transformer's current, it turns into a little arc lamp
because the voltage rises too fast for the contacts to open.
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I don't understand.
If the contacts don't open where does the arc come from?
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Inductors are constant current sources for small periods of time. As
the relay contacts begin to separate, the voltage will rise as fast as
needed to maintain current flow. It draws a very tiny but brilliant
little arc. The arc doesn't quench because the coil provides negative
feedback, keeping the gap the perfect size for that tiny arc.
It's how carbon arc lamps work. You can try it with a relay and an
inductor now. It might chatter as you'd hope for a while but eventually
it will fall into a steady state of an arc. (A relay by itself usually
doesn't arc because it has a shorted path in the coil to reduce
inductance.)
A capacitor slows the rise of voltage so that the contacts can finish
opening without arcing.
There are a few working variations of the relay transformer driver.
It's how tubes were driven from batteries in the old days. (Hint: add a
capacitor)
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Actually, in the old days, B+ for the tubes was obtained from a
low-voltage battery (usually a 6 volt "A" battery) and a vibrator
driving the primary of a transformer.
Here's a beauty for your perusal:
http://www.tubebooks.org/Books/mallory_vibe.pdf
They were also used as synchronous rectifiers, so the rectifier tube
could be done away with:
http://www.radioremembered.org/vpwrsup.htm