# Re: Cap safety & spark gaps

```Original poster: BunnyKiller <bunikllr@xxxxxxx>

hmmm  okayy..

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a ballast controls the current flow to the caps during the charge session, reduce the current flow thru a ballast and the cap wont charge to its full potential, thus reducing the total energy the cap can deliver to the primary when the spark gap fires (in a rotory gap situation) but given the situation in where the spark gap is a stationary gap with air flow, the voltage build up in the cap is dependant upon the width of the static gap setting. The wider the gap the higher the voltage is required to fire the gap into conduction which results in a higher voltage on the cap. Once the cap voltage is high enuf to arc across the static gap width then you have a pulse of current thru the primary to be induced into the secondary to produce the streamers... this may take several "sessions" of voltage build up to do this..and in this build up of several sessions, the voltage in the system can build up to a few times higher than the output of the transformer.. ( this is one thing I have yet to understand) ...
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as far as str or resonate rating of a cap compared to the transformer, there is very little to do to reduce the situation of ring-up on the charge cycle other than by reducing the current flow to the cap via an inductor or resistor or by going to a LTR cap( resistors lower voltage and produce massive amounts of heat as to where inductors reduce current and produce less heat.... that why inductors are the better way to go to reduce current flow..) and allowing the gap to fire before the peak is allowed to happen (( basically we are back to a narrow width static gap setting))...
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as far as your second question... a ballast controlled situation is not unlimited... a ballast controls the amount of current that is applied to the cap during the charge session... in a crude attempt to explain a ballast, it is an AC resistor due to magnetic flux resistance in the core the ballast is made from. short simple but not too explanitory... there is alot of math that is involved and I particularily dont care for the theoritcal math that is involved in AC applications ( too many letters that dont = the numbers) ;)
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you can use a ballast to reduce current flow in a static gap situation but the thing to remember is that the total width of gaps combined will be the amount of "gap" the system will use to finally arc across to dump the cap charge into the primary...
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question 3 if using a static gap keep it close to minimal firing width to save the cap...
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here's a situation that I am in...
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my pole pig is a modified monster ... it is 2 14.4 KV trannies in series to output 28.8 KV at 240VAC but since Im using a variac system with increased output beyond 240VAC I can get close to 32KV out from the piggie to supply the primary and caps ( but then again I have the caps wired to handle 140KV total i guess that is my saving grace on my system) the cap set is LTR and will never go resonate on the pig inductance so I wont see a voltage peak beyond the 140KV the caps are rated for.... I suppose this is why my Maxwell caps that are rated for low pulse ratings are handling hi pulse rate applications... :) I use a rotory gap in my system but I have noticed that the spark gap will continue to arc from the static electrodes from the moving electrodes to the copper band on the disc for an additional 1.5"s or so ... so in effect, the gap is extending itself way beyond the expected 100 thou gap the rotory gap is designed for.... it basically is pulling an arc to 1.5"... during conduction.
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the inductor is set at approximately 60A at 240VAC input ( about 15KW) and producing on average 10' ( free air streamers) and 14' streamers to a grounded object.... impressive to say the least for a "standard" T Coil.... eventually I am going to go solid state and see what I can do with my present set up ....
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hope this helped any more questions??? keep asking us eventually one of us will explain it to you where you can understand the answer
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Scot D

Tesla list wrote:

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```Original poster: "MIKE HARDY" <MHARDY@xxxxxxxxxx>

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Due to the recent discussions on safety gap, and air breakdown voltage, I need some clarification. Are you guys saying that if one has sufficient energy, and a resonant , or str cap, then charging voltage is dependent on spark gap length? This explains why output gets bigger as one opens the gap. So is this why a 35kV maxwell can blow with a 14.4 pig or PT? How does one keep there caps healthy in a ballast controled situation, where output is somewhat unlimited? I realize most ballasted coil configs use rotaries, but right now I'm using a sucker gap with my PT.
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