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Re: More arc simulations

Hi Terry,

> Original Poster: "FRITZ, TERRY" <terryf-at-ftc2.aei-dot-com> 
> 
> 
> Hi All,
>      I got the spice program to find the energy being dissipated in the 
> three main losses in my model.  The results are as follows:
> 
> Initial energy in primary capacitor = 3.41 Joules
> Energy into the arc = 2.097 J
> Energy into the secondary losses = 0.144 J
> Energy into the primary losses = 1.167 J
> 
> The secondary loss resistance is 270 ohms and the primary loss resistance
is 
> 3 ohms.  These are found by measuring the ring down times of the real 
> circuits and back calculating to find what resistance produces such a 
> ringdown.
> 
>      Apparently, the secondary resistance and losses or not very
significant 
> in system power loss.  However, the primary losses are extremely
significant 
> as we have suspected since the beginning.  This suggests that the loss in 
> the resistance of the secondary wire is of little concern (the DC
resistance 
> is 70 ohms in my coil).  However, the loss in the primary inductor's 
> resistance, primary capacitor's series resistance, spark gap, and primary 
> wiring is very critical.  This also supports the previous post showing that 
> as the primary current is increased, the losses also increase dramatically.
> 
>      At 120 BPS, the power dissipated in the coil is simply 120 multiplied 
> by the number of Joules from the above.  So from the initial 409 watts 
> input, the arc is getting 251 watts of power, the secondary is using 17 
> watts and the primary is burning up 140 watts (the high-Q ceramic caps, the 
> primary coil, and wiring stay cool, so I suspect the spark gap is the vast 
> majority of the loss).  The three ohm number for primary resistance came 
> from when I used my multi-gap spark gap.  I bet my new sync rotary has less 
> loss.  I will have to test this...
> 
>      The DC resistance of my secondary is 70 ohms but if I set the
quenching 
> to first notch with no breakout, it tests as 270 ohms judging from the 
> ringdown time.  This does not quite make sense in the real world components 
> and such.  I should probably set the primary resistance to the AC
resistance 
> of the coil and use a high value resistor from the output to ground to 
> simulate the secondary's natural no-breakout ringdown time.  The losses 
> would be the same but the model would then "look" more realistic since this 
> resistance could represent corona or dielectric losses in the secondary's 
> capacitance.  That would be about 10 watts.  This is not significant if the 
> coil is arcing but this resistance does insure the model will track the
real 
> coil's performance under non-arc conditions.  Of course, the skin depth of 
> the secondary wiring pushes the DC resistance up but I don't think it would 
> be as high as 270 ohms.  I'll have to sit down and calculate this 
> however....

I think your analysis is spot on. I have known for some time that the 
gap can be a monster and also I concur with your value of ESR for the 
secondary. It matches what I've measured on one of my coils to a tee.
Skin effect is not the only loss. Secondary ESR includes radiated 
losses, proximity effect in the winding, less than perfect ground, 
coupling to stray objects and probably others. As far as the primary 
goes, a paper analysis shows from the linear (macro envelope) 
ringdown that aims for best results for a desired primary energy 
include a high L/C ratio coupled with a high primary voltage. The gap 
loss is crudely characterized as a V*I loss, not I^2*R where V is the 
gap conduction voltage. This does go down as gap current increases 
but the relationship is not linear - effective Rgap climbs as Igap 
climbs. Vgap also tends to asymptotically bottom out much above 10 
Amps according to an arc characteristic in Sargent and Dollinger's 
High Power Electronics.
    The most dramatic demonstration of the truth of this I ever did 
was to compare the ringdown from a low-L high-C coil with that from
high-L low-C coil where the high-L coil was wound with thick Litz to 
keep proximity and skin effect to a minimum. Ringdown times and linear
slope were vastly different. A gap was included in each circuit of 
course. From memory, the gap went out in the low-L setup after 50uS or
so compared with 1.2mS for the high-L setup. Not only is the initial 
primary loss during first transfer minimized with the high Xp but if a 
further round of transfers occurred, the primary became a much more 
efficient holding pen for the energy.

    Acknowledgement: Mark Barton who used to be on this list was the
first coiler *I knew* who reasoned that a high Xp was a desirable 
attribute. There were probably others I was not aware of. We jointly 
investigated this a couple of years ago. Further experiments without 
the gap showed a dramatic improvement in raw Q if the primary was 
elevated considerably from the ground or mounted perpendicular to it.

Malcolm