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Re: Latest coil
Hi Alan,
There is a bit of controversy about what causes racing arcs. However my
thoughts are as follows.
I would raise the secondary rather drastically (like 10 inches) and work
my way down an inch at a time until I find the point were the arcs start.
Then back of an inch or two from there. Your coil dimensions are pretty
large and I bet you need around 3 inches of clearance above the secondary.
By starting with a large clearance and working your way closer, you
minimize the arcing which is obviously bad for your coil.
A few days ago there was the "Best Method" re post of how to measure
coupling (subject RE: Coupling) but I bet you can give pretty good
clearance and still be fine.
I think racing arcs are caused by too much coupling allowing transformer
action to create too much voltage on the secondary and it arcs. Others
think it is due to static electricity buildup. Moving the secondary
farther away from the primary is a sure way to stop it. Tuning may have
something to do with it too but you have to stop it before you can go
playing with other factors.
Cheers,
Terry
At 09:03 PM 09/03/1999 -0400, you wrote:
>Hello everyone. I thought I would post a little about my latest coil.
>The primary is flat with 3/8" tubing with slots in the form to allow
>tapping from below. The secondary is an upside down polypropylene
>trash can that measures 14" diameter on the bottom and 13" diameter on
>the top and wound with 18gauge magnet wire for 24-1/4" winding length.
>Two toroids are being used, a corrugated drain pipe wrapped with tin
>foil that measures 4"x33", and two flexible ducts taped end to end for
>7"x 40". I am using two of the H&R transformers that are wired
>anti-parallel for 10kV 300ma. Six sets of polypropylene caps, .013uF
>each for .078uF or so total and a sync-gap. This isn't quite resonant
>yet, but will soon be larger than resonant.
>
>The first run was just to see that everything worked. There were
>serious racing sparks and as I found out, several spots had burnt.
>Some turns had to be removed on the bottom and the other spots had the
>burnt insulation scraped off and were coated with model paint. Trying
>again the next night, one of the repaired spots burnt again and three
>turns had to be removed. But there was a ground strike before shutting
>down that I later measured at 80". Or 3.2 times the winding length.
>Pretty decent, but will have to get better :-)
>
>I setup again tonight with the newly repaired secondary, freshly
>soldered and re-painted. More racing sparks and some that jumped
>straight down to the primary from the lower toroid. Since I have never
>had these kinds of problems, I didn't really know what to do. I have
>only run with crappy capacitors before that wouldn't let the power out
>to the coil and these polypropylene caps are working great. I tried
>raising the secondary some more to reduce the coupling. It was now
>1-1/2" above the primary, but still had the racing sparks. The only
>other thing I could think of was to lower the toroids some. Now the
>racing sparks have been eliminated. But the spark length dropped,
>probably from the reduced coupling. I'll try increasing the coupling
>in a few days and see if the spark length comes back up.
>
>So, any comments or suggestions? All welcomed.
>Thanks,
>Alan Jones
>_____________________________
>ajones-at-pointlink-dot-net
>ICQ #21057220
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