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Re: About new gap design
Tesla List wrote:
>
> Original Poster: Esondrmn-at-aol-dot-com
>
> I haven't seen any response to my post listed below. Is there any chance
> this gap will outperform my existing async rotary? What about heat? Will I
> need to make this out of something that will stand a lot of heat, like G10 or
> maybe bakelite?
>
> Thanks, Ed Sonderman
>
> As I mentioned the other day, I am designing a new linear gap for my 6" coil
> running at 7 kva. I am curious to see if this gap will quench and to compare
> it's performance against my async rotary. I plan to use 11 of the 1.0" dia
> copper tubing coupling pieces for a total of 10 gaps. I will also use a
> vacuum motor to create strong air flow through the gaps - for quenching and
> cooling. I plan to design the gap so the copper pipe sections are gapped at
> .030" by using small spacers between them at the ends. By changing these
> spacers, I will be able to adjust the gap distance.
Perhaps I can be of some help:
Http://home5.inet.tele.dk/f-hammer/sparkgap/sparkgap.htm
This shows my experience with this kind of gap. I do not recommend that
you have spacers between the tubes, at the ends of them. I feel sure
that almost anything would carbonize, if it is placed there. At 7kW you
are going to see the whole gap area filled with uniform arching. In my
case, I had about 4 mm =1/6 inch of spacing from the ends of the
electrodes and out to the bars of plywood that were clamping the
electrodes, and still, the heat and ionization around the ends of the
electrodes would attack the wood, and finally make it carbonize, and arc
trough to the other row of electrodes. With just one row of electrodes,
some of this problem will be eliminated, but these gaps get hot really
quick, soo....
As for cooling, I would recommend that you divide your efforts into 2
directions,
1. relatively small airflow trough the sparking area, to remove ions.
Too much flow here will decrease your performance, and even the fiercest
flow will be too small for enough cooling. A vacuum cleaner motor is
very suitable for this task, variac controlled.
2. Another fan blowing trough the tubes lengthwise. With a manifold that
directs the air into the tubes, without disturbing the gap area, you can
apply a tornado here, to get good cooling, and you are going to need it.
When I ran the amacord, which had 30 gaps, at full power, producing 8`
discharges, it got hot after 1 minute of running. A fan from a big
microwawe oven will suit this task well, as you are going for flow, not
big suction.
>
> I am running a 14.4 kv 5kva distribution transformer at about 7 kva. I am
> not exactly sure what the output voltage is but know I have some primary
> losses due to the inductive and resistive ballast. I am also using the
> higher output tap on the variac, so for sake of discussion, let's say the
> output is 15 kv. This would be 21,200 volts peak to peak - so the cap would
> charge to one half of this or 10,600 volts. How do I determine how wide I
> want the gaps set to fire at about 10,000 volts? Is the .300" that I have
> planned close?
This is not entirely right, actually the P-P is 2,82 of the RMS voltage,
so you have 15*2.82=42.3 volts P-P, however this translates to + -
(15*1.41) =21.15 kV
So you will be able to charge your cap to 21 kV at least. You determine
the breakdown voltage of the gap, by putting it across the transformer
without anything else connected, and turn the variac up, untill the gap
fires. If it does so at the max. variac setting, you have it right.
>
> How about heat dissipation? How hot is this gap going to get? I recall
> someone saying that the gap eats up about 7% of the available primary power.
> Is this close? Does that mean that I will have 7% of 7kva or about 500 watts
> dissipated in the gap?
Very hot!
I think I said it before, blow the tubes lengthwise for the best
cooling.
Hope this has been of some help,
cheers, Finn Hammer
>
> Thanks, Ed Sonderman