[TCML] A Safe Tesla Coil - was: Tesladownunder update, briefcase coil, lots of sparks etc

[Derek <tesla@xxxxxxxxxxxxxxxxxxxxxxxx>]

Peter,
   I'm sure from the construction pictures of your coil that a 
dangerous failure is unlikely and ensuring the subject is holding an 
earthed neon is a good way of minimising the risk.

I have been searching a way of making a "safe" tesla coil for a while 
from the point of 'the sparks can't kill you' . I know about RF heating, 
skin effect an the other associated dangers of high voltage RF. I know 
it can't ever be totally safe, but if you are using a coil as a 
demonstration piece the possibility always remains that you or a subject 
will come in contact with an arc.

So far my attempts a making a safe coil have resorted to designing them 
battery powered to eliminate the danger of mains connecting to arc by 
whatever means.

   I too have been skeptical about the primary-secondary arc increasing 
the arc current. I have always used the possibility as a worst case 
scenario when thinking about coil safety. I had wondered if the Henry 
Transtrom case was caused by a faulty secondary earth which would make 
more sense than purely a secondary-primary strike in  a solidly 
constructed TC. Maybe one of the historians in TCML could shed some 
light on this.

I'm not too sure I would trust PVC pipe either as a good insulator at TC 
frequencies, I have a number of small coils with PVC primary formers 
burning through or around to the secondary.

Maybe an earthed spiral metal shield between primary and secondary would 
help to remove the possibility of primary-secondary arc over/through.

   Cheers
      Derek

Peter Terren wrote:
> Hi Derek
> Firstly, mains earth is the RF earth and goes to all the metal in the 
> briefcase which is the centrepoise. Secondly, spark length is such 
> that it is just not going to connect through the PVC pipe surround 
> separating the primary and secondary. The primary is fully enclosed.
> Child use means the child holding a small neon tube that is earthed 
> and drawing sparks. It is hard to imagine a circuit path that will be 
> a problem in this situation.
> I have always been a little skeptical about the situation you describe 
> anyway. Simultaneous sparks from primary to seconday plus toroid to 
> subject seem a bit far fetched. The circuit path for a mains = RF 
> earth would be very largely in favour of flow through the base of the 
> secondary rather than through the subject.
> Do you (or anyone) have reasonable evidence that this has increased 
> secondary current and if so why aren't we exploiting this all the time 
> to increase our TC sparks?  I am aware the Henry Transtrom was said to 
> have been killed in this way but I would have thought it was just a 
> high power coil that was the problem.
>
> Cheers
> Peter
> www.tesladownunder.com
>
>
> ----- Original Message ----- From: "Derek" 
> <tesla@xxxxxxxxxxxxxxxxxxxxxxxx>
>
>
> > Peter,
> > ..... I am interested as to how you have made this coil safe "for 
> > supervised children to use". I realise that the power levels and 
> > performance mean that the risk of electrocution directly are very 
> > small, but to my mind the most dangerous aspect of you coil is the 
> > possibility of a primary to secondary arc whilst a "tasting" was in 
> > progress. In this case there is a very real danger of connecting the 
> > 6Kv@30mA output from the NST via the secondary and arc channel to the 
> > "taster".
> >
> > Have you designed the coil in a way to limit or prevent this 
> > possibility ?
> >
> >    Derek
>
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