[TCML] Re: Spark gap Resistance

[Barton B. Anderson]

Hi Bert and Greg,

I didn't realize 4 series gaps were used. This would certainly add to 
the complexity of the measurement.

I would have expected something on the order of 100V drop across the gap 
mainly due to a paper regarding spark gap losses using a Marx unit 
(Determining the Losses in Spark Gap Switches, IEEE). Although the gases 
(Argon, Argon/Oxygen) did change the voltage drop, it wasn't excessive. 
The voltage drop was quite low at about 135V for 4kV at 159kA. Spark gap 
resistance was much lower on the order of 0.00424 ohms. Significantly 
lower than Greg's 0.65 ohms. Although I do expect losses in spark gaps 
in an RF situation to be higher, I don't expect it to be that high.

Take care,
Bart



Bert Hickman wrote:
> Hi Bart and Greg,
>
> I also found it very interesting that Greg saw a 2700 volt drop across 
> the primary gap. "Short" gaps used in Tesla Coils typically drop only 
> 150-250 volts/gap. Since Greg's primary rotary gap actually consisted 
> of four spark gaps in series, he was measuring about 675 volts/gap. 
> However, this included the combination of electrode resistances, gap 
> wiring resistance, actual gap voltage drops, and the total inductance 
> of the rotary gap.
>
> I suspect that the abnormally high voltage seen across the firing gap 
> was due, in part, to the effects of the abnormally large peak current 
> through the electrodes (tungsten?), and the associated gap and wiring 
> inductance. The latter might have had a disproportionate contribution 
> to observed voltage drop due to the relatively low inductance of the 
> remaining primary circuit and the high di/dt in the original primary 
> circuit. It would be interesting to see what the voltage across a 
> single spark gap might be in comparison when running at similar 
> current levels.
>
> Bert