# Re: sstc driver help

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Hi Gary,

> 500 W will not make a very long spark and will not break out of a large
> toroid. I would guess you are looking at a maximum of a 4 inch diameter
> secondary and a 6 inch diameter toroid.

I consider a long and thin secondary, without any respect to spark gap
coil H/D ratios. Should work... In style of "helical resonator" as used in
old HV demonstration labs.
I had planned some sort of large but flat pancake as toroid.

> Watch out for input impedance considerations.  The coils I have built have
> input impedances in the range of 30 to 120 ohms.

Lets see, my 8 turn primary gives 0.147mH * 2pi * 200kHz = 185 Ohm, so
about 2 A in at 300VAC square wave(?).

> If you apply a square wave with rms value of 3 kV to a secondary with
> 100 ohms impedance, you get an rms current of about 30 A, or a power of
> 90 kW.

Do you mean possible current draw from the transformer secondary, or
feed into the TC secondary?

The transformer secondary at 120 turns gives 1.5mH * 2pi * 200kHz = 1885
Ohm... so oops!... 5kV/1.8kOhm => 2.8A => 14kW...

> If you are power limited, you may be designing for too high a voltage.

Yes. The line is maybe 5kW max, counting in all additional household
equipment running from it...

> I run up to 30 kW into my coil, but it does not require more than 1000
> to 1500 V input.

Cool!
Although, I had the impression that higher voltage is better, with
less R*I^2 losses into the TC secondary wire resistance?

> At resonance, input current is in phase with input voltage to a secondary. I
> use a current transformer to monitor current.  When it is maximum, the top
> voltage is also maximum.

Ok! I'll build one, with good insulation...

> I started by using a full wave bridge, but instrumention is simpler with a
> half bridge.

Thanks for the tip! I'll try to get that half bridge running.

--
*************************************************
Jan Florian Wagner
http://www.hut.fi/~jwagner

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