Re: SSTC update

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Jan Florian Wagner by way of Terry Fritz <twftesla-at-qwest-dot-net>" <jwagner-at-cc.hut.fi>

Hi,

> Im using a 2 resistor type adjustable duty cycle config.The coil seems to 
> resonate with R1 being 9KOHMs and R2 being 3.3KOHMs.The capacitor is a 
> ceramic disk 470pF.I dont know its frequency.If someone has a calc that wil 
> use capacitor values below  .005uF, will you calc this for me?

Isn't there a formula in the LMC555 or NE555 datasheet? www.national-dot-com

If it says "not valid below 5nF" then you have to measure the frequency
yourself... :o(

> My coil DOESNT like top capacitance for some reason.Why?I add small amounts 
> and then retune and get poor output.

Well somehow there seems to be an "optimum" capacitance. I would imagine
that the "optimum" depends on your interruptor frequency and input
power, as well as how smooth the topload surface is. I don't know, maybe
someone has already derived a formula for the relation?

> My MOSFETs seem to have stopped their overvoltage deaths(Still no snubbers 
> except i have a .047uF Ceramic cap across the drain and source).

Congrats! :o)

> It gets real 
> hot when i give it a lil juice.I had solved this with a MOV until it burnt 
> up:-( WHY?

The MOV burnt? Then you probably have too high voltage spikes with
considerable power. Is the MOV rated two times the peak input voltage to
your SSTC?

> Anything else will help it?I had read about that on a site that deals
with an 
> IGNITION coil circuit.Thats why i have a .047uF cap across the MOSFET.

An ignition coils doesn't behave like a SSTC!

> Sometimes this coil detunes.How can i stop this self-detuning?

If you find out how to do it, please tell us! ;o)

Well actually this IS a big problem. An experiment: tune the coil, have it
running, the slowly bring one hand closer to the secondary (not TOO
close, of course) => watch streamers shrink.

Also, tuning the coil today doesn't mean it will still be in tune
tomorrow. It seems to me like it depends on the surroundings, the
grounding, weather, moon phase, and what you ate for lunch...

The higher-frequency your secondary coil is, the easier it will detune. 

There's no real way to stop this. :o(

You just have to keep on retuning... Either manually or automatically. The
"automatically" part is a bit tough to do, though. With manual, your
circuit can be small. With automatic, it ain't small.

cheers,
 - Jan

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