Re: SSTC probs

["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 11/23/01 10:01:19 AM Eastern Standard Time, 
tesla-at-pupman-dot-com writes:

<<  Well, got done winding a large coil in hopes of lowering its self 
resonant 
 > frequency.Its 4.5in diam by just under 12 inches long wound with 28AWG
 magnet 
 > wire.I have no way of measuring the frequency.(Anyone know an estimate?)Im 
 > guessing 400khtz?I hooked it up and get pretty powerful little arcs about 
 > 1inch long?Why?When i turn up the voltage on my variac, the arcs dont get 
 > longer but get HOTTER and sound like race car engines reving up.(Pretty 
 > amusing).
 
 You shouldn't need to guess at Fr - this list and its resources are 
 alive with well-tested formulae which agree with each other. How many 
 turns on your secondary? That is the only other piece of information 
 we need to know if your running with no topload.
  
 > I got the IRF740 to take about 70 volts and then POOF!No smoke or 
 > anything.Just failure.It looks perfectly fine.Replace it and im back in 
 > buiseness.It doesnt even get hot when it fails.WHY?
 
 Too high a voltage between source and drain suggests itself. A scope 
 would get the answers in no time.
 
 > The 555 pulse circuit is using a 102K capacitor(.001uF right?) for timing
 and 
 > 2 1k resistors in series with 2 10k pots.Shouldnt this be good for up to 
 > 480khtz?
 
 ? Get an application data sheet, either from the manufacturer's 
 databook or maybe the web. There must be something out there. You can 
 calculate the component values needed to make it work at the 
 frequency you want. Is it a standard 555 or CMOS version? Got a 
 circuit we can see?
  
 > I tried puting on a big toroid on top of the coil(12in diam by 4 in 
cord).It 
 > only hurts the output.Why?I thought it would bring down the frequency
 further 
 > allowing me to further tune the coil in to resonnance.
 
 Are you coupling the MOSFET to the secondary via an untuned primary?
  
 > So, total results from my little 555+IRF740 MOSFET setup is 1inch orange
 fire 
 > arcs.Is this good for a simple 555 setup?Or am i missing something?
 > Thanks for all your help,
 > PS-this thing is dangerously putting out current.Cant I lower that?Im 
scared 
 > to go close to it when it vaporises needeles and such.
 
 We need some information to troubleshoot your setup.
 
 Regards,
 Malcolm >>
Hi, I do not have an O-scope.

I do know that the 555 should be able to go up to 480khz with the parts i 
selected.I found a java script calc for that.
I am using 8 turns to the primary.
There are 740 turns of wire.28awg, 874feet
When I turn the little pots, it seems to be best at their lowest setting.It 
seems as if the coil wants an even higher frequency than the 555 config is 
running at now.Maybe if I changed it it would help.I have a Lm555CN.

I have just added a meatl bowl(SMALL) on the top of the coil and it puts out 
longer but VERY thin wimpy sparks and does its little detune buiseness.Is 
there an easy way to auto tune this coil?

Thanks for your help,
Matt