Re: Power curve
Subject: Re: Power curve
From: mrbarton-at-ix-dot-netcom-dot-com (Mark Barton)
Date: Fri, 17 Nov 1995 03:54:49 -0800
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> Not sure if you are including this in your calculations
>but if you make a "resonant charging" circuit such as you
>describe rememb er that the voltage on the capacitor will
>end up at TWICE the input DC voltage. That assumes that when
>the spark fires it discharges the capacitor to zero voltage.
>Standard radar modulator circuit and has been built by the
>millions. However, wonder what you plan to use as a charging
>choke that will withstand that much voltage?
> Seems to me the beauty of such an arrangement is that
>you can make the spark frequency completely independent of the
>power supply frequency (assuming you have a large enough filter
>capacitor), and still get a nice regular series of sparks. I
>have been thinking of trying something like that here, just using
>a half-wave doubler from each end of a 15 kv transformer, paralleling
>the outputs to get around 18 kv DC, still average current limited
>by the transformer reactance. I have an old radar charging choke
>which I think will take the voltage, but not sure.
> If you ever try the experiment, please let us all know
I have built this exact arrangement and ran it at 25-50KVA. It works
fine. The only difference was that I used a 4 diode full-wave bridge
in the power supply. The filter cap was 7uF/40KV. The choke was home
made by winding multiple sections on a 3' x 3" ABS pipe. Each section
was about 1.5" long and were kept separated by 8" squares of 1/8"
plexiglass which had 3" holes fly-cut in them so they could be stacked
on the pipe and siliconed in place. Each section was scatter wound
with 22awg 1KV stranded hookup wire out to a diameter of about 6".
Straight transformer laminations ran down the pipe for its entire
length. Moving this core in and out provided variable inductance. We
got about 5 Henries out of the thing. That's the ballpark these chokes
have to be in. If you use a smallish primary cap, you must use a
bigger choke still (to maintain the time constant). A diode was in
series with the choke to prevent the primary cap from discharging back
into the filter cap during the backswing of the resonant charge cycle.
The system worked fine, however I saw no real advantage over the AC
charging system, especially if the interrupter break rate is
significantly higher than the line frequency. I will still use DC, not
for the sake of resonant charging, but because I want to voltage double
the transformer this time!