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Re: [TCML] Re: Spark Gap Resistance

Hi Dave,
Yes, the primary resistance in my analysis is rather high in general. This is exactly why I asked Greg if the measurement was across the gap or across the entire primary circuit (just me trying to account for the high ohmic value).
I agree that as the plasma channel increases with temperature, it's voltage drop should decrease (but there are probably specifics I don't understand about high temperature plasmas). In Greg's case, his primary is large and frequency is low. AC losses are low in this system, yet there are still some RF effects of penetration depth and the associated ohmic losses of the primary, so there are some losses on that account. Our normal sized coils are considerably higher in this area and that's where my real concern is. I see the gap as a high loss (don't get me wrong about that), but I think the primary has it's share of losses as well (including wiring and connections) which are simply not accounted for (and I would like to account for them). The problem for me in doing that is the mechanical structure and associated thermal variations. I'm simply in arm chair brain mode at the moment. 

Take care,
Bart





David N. Van Doren wrote:

Thanks for the response Bart
What led me to say that .65 ohms seems low is that comparing my modeling
with Richie Burnett's Real Tesla coil wave forms seems to match best with
about 2-3 ohms total primary resistance. This is based on my small study
coil. Granted that visually comparing RF burst ring down rate is not very
precise, but .65 ohms just doesn't fit. It is possible that the higher currents of 
Greg's coil  make a hotter plasma in the spark gap and hotter plasmas
tend to be of lower resistance. Suffice it to say that my spark gap heats
up faster than any other part of my primary circuit which would imply the greatest losses. ----- Original Message ----- From: "Barton B. Anderson" <bartb@xxxxxxxxxxxxxxxx> 
To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx>
Sent: Saturday, December 08, 2007 1:57 PM
Subject: Re: [TCML] Re: Spark Gap Resistance



Hi Dave,
0.65 ohms is not low, it's very high! Look at I^2R across all four gaps for 2.9 MW per gap! Bert attributed the possible high values to the impedances of the gap between all 4 series connections which is really the only other place to attribute such a large loss. I have my doubts on the accuracy of the 0.65 ohm value because it just seems too high even with the impedances of the rotary between the 4 gaps (because I expect Greg would have made those areas very robust).
I personally would expect total gap resistance in the range of 0.1 to 0.2 ohms for the 4 total gaps.
The 0.65 ohms value might be accurate, but if it is, then losses are likely in the impedances of the rotary and they are very significant. 

Take care,
Bart

David N. Van Doren wrote:

Greg
.65 ohms for a spark gap seems very low. But then again that is an unusualy large coil, with a very large cap and charge voltage. I don't think this is very representitive of the average coil tho. Such a low gap impedence must be a result of such high currents and large amouts of ohmic heating of the plasma in the gap reducing it's resistance. You also reference silicon switches used in your 90L10K prototype coil, having an effective impedance of 5milli ohms. Just what were these switches? 

Thanks
Dave _______________________________________________
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