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Re: 24 turns center tap neon primary.
Tesla List wrote:
> I also discovered that you can not build a DC to AC converter using SCR's.
> It won't work. When the SCR is triggered it won't open again until the
> power it turned off. After about 2 seconds every solder connection melted
> and the entire circuit fell apart into a pile of parts on the work bench. I
> didn't know what happened the first time so I soldered it all back together
> and did it again. Its a little funny, wish I had it on video tape, the
> circuit is soldered together one second, then all at once the entire thing
> falls apart all by itself. Look its magic.
Actually you can but you must include a commutating SCR. The simplest circuit
is
to parallel the main scr with a second one in series with a cap. The cap is
chosen so that it will conduct the load current long enough to allow the
primary
SCR to commutate. When it is time to commutate, the commutation SCR is fired.
The current is diverted away from the main SCR which turns off. When the cap
is
charged, the commutation SCR turns off. A discharge transistor (or resistor)
discharges the cap and the cycle repeats.
A different scheme uses an inductor to induce enough bucking EMF into the SCR
line to stop the current long enough for the SCR to commutate.
The first scheme is very old. It is used in the 60s vintage UPS's used in
Westinghouse nuclear reactor systems. All the logic to make it happen is plain
old transistor. These inverters were bullet proof.
With modern IGBTs and power FETs, SCRs are of less importance but if you happen
on a box of husky SCRs at a hamfest, rest assured that they can be used for
inverter service.
John
--
John De Armond
johngd-at-bellsouth-dot-net
Neon John's Custom Neon
"Bendin' Glass 'n Passin' Gas"