Re: SSTC update

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

Original poster: "by way of Terry Fritz <twftesla-at-qwest-dot-net>" <Fucian-at-aol-dot-com>

In a message dated 1/21/02 1:19:31 PM Eastern Standard Time, tesla-at-pupman-dot-com 
writes:

<< 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
  >>
Ok no wi soldered it onto a proto baord and the output 
SUCKS!!!!!!Why?EVERYTHING is the same.MAybe the traces are just too small?

I was getting close to 4in output with like 70volts in and was using a large 
harddrive disk as a toplaod.Now it stopped doing that great performance.Back 
to the trial and error.It seems the solderless breadboard is the only thing 
aside from etching a real baord.

About the detuning, it seems there is a spot or comboniation of the tuning 
that keeps it happy.There are several spots in the pots that results in a 
flare up of corona, it just detunes when i THINK of getting close to it!LOL!

About the MOV, no it was rated for the double input.I guess if i get the 
highest possible voltage It should solve the hot MOSFET probs?

Oh well, more tinkeringto do....

Matt