[TCML] Re: Spark Gap Resistance

[Barton B. Anderson]

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 at classictesla.com>
> To: "Tesla Coil Mailing List" <tesla at pupman.com>
> 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 _______________________________________________
>>> Tesla mailing list
>>> Tesla at www.pupman.com
>>> http://www.pupman.com/mailman/listinfo/tesla
>>>
>>>
>>>
>>>
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