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Re: Twin SSTC (fwd)
---------- Forwarded message ----------
Date: Sun, 08 Jul 2007 21:21:22 +0200
From: Finn Hammer <f-h@xxxx>
To: Tesla list <tesla@xxxxxxxxxx>
Subject: Re: Twin SSTC (fwd)
> Forgive my question, but why do you have to have a trigger for all the
> SISG stages? Wouldn't triggering only one stage (for practicality, the stage
> closest to ground) overvolt the remaining SISG stages into conduction?
> -Phil LaBudde
> Center for the Advanced Study of Ballistic Improbabilities
Many people have asked the same question, and I`l try to make it clear.
Each SISG section holds 4pcs. 250V Sidac`s, so they self trigger at 1000V.
Suppose I start out with a 4.9kV DC supply.
The first time I trigger the stack, this is the voltage on the primary cap.
There is a charging inductor downstream, so after the first ringdown,
and during the second charging cycle, the capacitor attains a voltage of
I therefore need a 10 stack of SISG sections to hold off the operating
To trigger the first ringdown, I`d have to trigger 6 sections, leaving
4.8 kV across the remaining 4 selftriggering SISG sections.
This would also make it a coil that could only run at near full power,
which I don`t like. Terry and others have reported how it is unnerving
to witness a SISG coil burst into life without warning.
So this is what I did:
Each Sidac has 2 sections, so there are 8 sections of 125V to do good with.
By shorting the bottom 7 sections with a SCR, I can produce output from
the coil at only 1250V on the supply, running at 2500V on the primary cap.
And still increase the voltage up to just below 5000V without getting to
the point where the SISG sections self trigger, because at that point
the breakrate increases instantaneously, often up to 1250 BPS.
With these measures, the coil is as docile as an ordinary DC RSG coil,
powered up with a variac, but still has the virtues associated by a
solid state switch.
So although the DC supply dictates more triggered sections than one
would tend to think necessary, an equally good reason was, that I wanted
to be able to trigger the coil at the lowest voltage possible.
Cheers, Finn Hammer