Re: Recent power arc experiments

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Original poster: "Bert Hickman by way of Terry Fritz <twftesla-at-uswest-dot-net>" <bert.hickman-at-aquila-dot-net>

Boris,

A very interesting experiment! However, I suspect that the relatively
small physical size of the individual resistors (1500 ohm at 5 watts)
and the high applied transient voltage were likely the source of the
measurement problem. 

Instead of going through the resistive element, the transient voltage
across each resistor most likely rose to the point where the element was
bypassed ("jumped" around) or was internally overvolted and broke down.
The former is likely with an inductive wirewound, while the latter is
probable with a carbon body or film resistor. Since the voltage standoff
limit of any resistor is a function of its element length, unless these
were specially made long-bodied HV resistors they most likely
over-volted and broke down during the transient. This would force more
power to be dissipated in the airborne spark to the resistor chain,
accounting for the reduced Joule heating in the chain. 

I observed something similar during an experiment some time back where a
120 volt 25W tungsten lamp was inserted in the current path between the
toroid and a breakout wire. When current flowed through the lamp to air
streamers, the lamp would light at a certain average brilliance.
However, when power arcs were drawn from the wire, the lamp would
actually get dimmer! Turns out, that under the higher current
transients, the voltage developed across the filament was sufficient to
cause (hidden) spark breakdown in the base of the lamp, thereby
bypassing current flow through the filament. Using a linear halogen bulb
solved the problem. 

It would be interesting to duplicate the resistor experiment with a
chain of longer HV resistors capable of withstanding the peak transient
voltage. Another alternative might be a long, small diameter water
resistor.

-- Bert --
-- 
Bert Hickman
Stoneridge Engineering
Email:    bert.hickman-at-aquila-dot-net
Web Site: http://www.teslamania-dot-com

Tesla list wrote:
> 
> Original poster: "boris petkovic by way of Terry Fritz
<twftesla-at-uswest-dot-net>" <petkovic7-at-yahoo-dot-com>
> 
> Hi All,
> 
> The result of following experiment,fellow coiler
> conducted  recently,seems bit strange (at least for me
> ,since I suggested him to do it estimation vise).
> 
> According to the instructions, he hung ,verticaly,
> above 10" spherical terminal of his coil several
> resistors and grounded them via wire in a celling.
> Between  sharp point on the top of the sphere and
> string of resistors there was formed variable gap that
> way.
> For the particular coil and power level used,it was
> found to be most convenient to use 19" gap spacing.
> At this stage ,attached arc would be quite stable and
> could last for quite a time without deattachment.
> The string of resistors was made of identical parts-
> each resistor rated 5 W-1500 ohms.
> 
> Now,the strange part.
> Experimentally,by low frequency test,it was found that
> ,if forced to dissipate 10 W ,these resistors
> considerably  get warm.
> Since ,there were 9 of them put in series,90 W would
> do a nice heating effect to them (very soon).
> But,nothing of the expected heating was noticed.
> The experimenter,after few minutes of TC run turned
> the power off,and touched the resistors.
> They stayed reasonably cool.
> 
> Used input power level for that and other experiments
> was always the same -about 650 W.
> This is a nice classical TC system;with 300 BPS
> rotary,20"*6" closewound secondary and by using 650 W
> it can occasionally  develop 36" point to point arcs.
> 19" spacing provided for the arc the most stable
> condition with  the dimmest primary gap light running,
> though.
> The result of all said :Total string resistance
> 9*1500=
> 13500 ohm consumed less power than secondary power
> arc.
> This is very much in confrontation with usual view of
> the impedance ballpark of such arc.
> Anybody else performed similar expertiments,and
> wondered why there wasn't any smoke where it had to
> be?
> Any comments ,and thoughts on this would be welcome.
> 
> Regards,
> Boris
> 
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