Subject: Insulated secondary
From: richard.quick-at-slug-dot-org (Richard Quick)
Date: Fri, 20 Oct 1995 02:09:00 GMT
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> Did you ever get the message below?
Yes, and sorry, it has been another very full week. I was out of
town last weekend, and am just now catching up.
> I wrapped my secondary in saran wrap this weekend (glad wrap
> actually). I put 40 to 50 wraps on it covering from the first
> windings clear up to the bottom of the toroid. It sure looked
> much better when you could see the bare coil - but I will say
> it works. I now get no discharges breaking out from the
> secondary. I had it running at about 8.2 kva. This is with
> the welder wide open.
So far so good.
> I tried the original 14" toroid sitting on top of the 40"
> toroid and still had many strikes into the primary which would
> fire the safety gap and scare the hell out of me - since I am
> sitting only a few feet from the safety gap. Then I tried the
> 30" toroid sitting on top of the 40" - same thing.
Yeah, a couple of megawatts popping across the safety gap to the
RF ground really shows off the brute force of capacitive
discharge circuits. That fear is healthy under the circumstances.
> I finally ended up running it with a couple of coat hangers
> laying on top of the toroids with just the ends sticking out
> over the edge. This stops that problem.
This has worked for me in the past also, but I have found that
the aluminum strips taped to the outer edge of the toroid,
forming an arch with a fairly sharp radius of curvature, works
> Since I added more toroid surface area, I moved the primary tap
> up to the 13 turn point. I believe this lessened the problem
> with the loud "pops" in the rotary. Maybe this is being caused
> by not being right on tune. Maybe the rotary is trying to tell
> me something. Since I don't have any equipment, I have just
> been tuning for best spark at low power and then cranking it
> up. Is there a chance the tune changes as the power goes up
> because the ion cloud gets larger? I never considered
> this before. This would mean a lower frequency at higher power
> levels and would need more turns in the primary - like maybe
> another 1/4 to 1/2 turn. What do you think about that?
I think you have made a very astute deduction. This is exactly
what I have encountered. 1/4 to 1/2 turn is exactly the correct
amount of additional primary inductance require to compensate for
the frequency drop in the secondary caused by ion cloud loading
around the toroid. The ion cloud is conductive and acts as an
extension of the toroid discharger. This condition is typical in
high powered coil systems.
> Winter is coming and I have pretty well packed up all my
> coiling equipment for a while. I think I have squeezed about
> all I can out of this 6.25" secondary.
I agree. I don't know of anybody who has extracted this much
performance from a 6.25 inch diameter secondary coil.
> Maybe it is time to start thinking about that new 10" secondary
> and a new flat primary. I think all the rest of my system is
> good as is - a new primary & secondary and I'm ready to go.
> With 8kva today I am getting 73"+ discharges, at somewhat
> elevated humidity levels. What would you guess the same system
> would produce with a 10" secondary?
The limiting factor is the toroid breakdown voltage. I would say
8-10 feet with a 10" diam. secondary and your existing toroid.
... If all else fails... Throw another megavolt across it!
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