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More magnifier runs

Subject: More magnifier runs
  Date:  Sun, 11 May 1997 18:27:09 +0000
  From: "Bert Pool" <bertpool-at-flash-dot-net>
    To:  Tesla List <tesla-at-pupman-dot-com>
    CC:  bemery-at-why-dot-net


Wild Bill and I did some very serious coiling last night.  We had a 
perfect night for outdoor coiling - 70 degrees and zero wind.  We set 
up the driver in the front driveway (driverway?) and setup to test a 
new toroid.  Since we crashed Bill's spun aluminum toroid a few weeks 
ago, I built a new 36 inch by 8 inch toroid out of aluminum flex 
duct.  We also removed the old 29 inch diameter primary and rewound 
it at 24 inches, giving us a new K of 0.39.  We had arcing problems 
with this, so we lowered the primary turns as far as they would go, 
dropping the K to about 0.32.  Our first tests were with the 20,200 
volt 2 KVA transformer that we've used in the past.  We got 
continuous 8 foot hits to an aluminum ladder.  We then pulled the 
20.2 kv transformer, and connected a 5 KVA 34,500 volt potential 
transformer.  We had concerns that the rotary would 
successfully switch this higher voltage, but the rotary handled it 
just fine.  Output spark increased only slightly.  We did find we 
have secondary to primary down strikes which had not been a problem 
with the smaller 20.2 kv transformer.  We went ahead and dropped the 
ballast resistance some more, which did improve the output spark a 
little.  We also tried our 62 inch by 8 inch large toroid.  We 
successfully broke out, but spark length was no where as much as with 
the 36 inch toroid.  No amount of tuning helped.  In an atttempt to 
get better tuning, we also tried using a 0.03 ufd tank cap instead 
of 0.015 ufd.  No significant improvement.  It seems we may be maxing 
out the current capabilities of our two layer 14 gauge secondary - we 
are seriously thinking about adding two more layers of wire, making a 
total of four layers, but we're not sure we can fit that down into 
our primary!  The tendency of the top of the primary to spark down to 
the primary is my main concern.  I see no good way to form a spark 
shield (something like the ribs on a hv insulator); indeed, extra 
height on the secondary is the only solution I see.

So far, 20.2 kv, 2 KVA input with 0.015 ufd and a 36 by 8 inch toroid 
has been our best combination, giving us really nice 8+ foot sparks.

In our attempt to reach 10 feet last night we came to a couple of 
conclusions:

1) Ten feet is a LOT longer than 8 feet, and is _much_ harder to 
reach than we ever thought.

2) Richard Hull, RW Stephens, Ed Wingate, Greg Leyh, et al., all  
have my new found respect for hitting and going beyond 10 foot 
sparks!  It ain't as easy as one would think.  Pumping in more power 
don't always get it.

The neighbors came out to watch.  We coiled until 11:30 p.m., and 
no one called the cops.  Big sparks, no major component failures, and 
we didn't have to sleep in jail on a mattress that stank of urine, 
so what more could a coiler possibly want?  10 foot sparks of course, 
but we'll get there.  It looks like we'll get there an inch at a 
time.

Bert Pool
bertpool-at-flash-dot-net