Re: Gap Losses (II) Re: Primary Heating

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

Original poster: "Malcolm Watts by way of Terry Fritz <twftesla-at-qwest-dot-net>" <m.j.watts-at-massey.ac.nz>

Hi Paul,

On 13 Mar 2002, at 7:59, Tesla list wrote:

> Original poster: "Paul Nicholson by way of Terry Fritz
<twftesla-at-qwest-dot-net>" <paul-at-abelian.demon.co.uk>
> 
> Malcolm wrote:
> > instantaneous Rgap is inversely proportional to Igap
> 
> Dave wrote:
> > Arcs have a negative resistance characteristic:  More current
> > means LESS voltage drop
> 
> I agree with both of you.
> 
> And I'm sure that you'd both agree that the energy lost into the
> gap over a cycle is the integral of V(t) x I(t), and that the
> Q is then 
> 
>  pi * Lpri Ipeak^2/integral{ V(t) * I(t); over the cycle}
> 
> for that cycle at least.  Has anyone used one of those fancy 
> digital scopes to measure this?  If so, did the gap energy lost on
> each cycle account for the ringdown envelope, or did you have to
> add in a significant fixed R.

In answer to your first question, no. In answer to the second, it 
would be interesting to know the relative proportions for different 
circuits. The unloaded Q of the circuit with the gap shorted would 
give an indication of circuit quality. One measured finding is that 
Q(unloaded) differs markedly depending on how high the coil is 
mounted above the floor. As you appreciated above, Q is no longer a 
fixed quantity with a gap in the circuit. The comparative losses 
might perhaps be found using thermal means. Intuitively, the gap 
loses the most but it is hard to tell with a short run as the copper 
has considerably higher heat capacity than air.
 
> Are there such things as tables or empirical formulas for gap
> losses - put in a current and the gap dimensions and pull out a
> figure for loss?

I'll have to check some works I have. I'd be surprised if some 
quantification wasn't done somewhere.

Regards,
malcolm