Re: fried neons
From: Steve Z[SMTP:zoidspc-at-erols-dot-com]
Sent: Sunday, November 09, 1997 11:01 PM
Subject: fried neons
After blowing up half of a 120ma 15kv neon on my coil I depotted
it and discovered that the winding was fried and it wasn't a "tar short".
Therefore I found some old books on transformer design and read up on the
subject. I beleive neon transformers burn out on TCs for 2 reasons.
First, neons are insulated with oil soaked paper between the
layers of windings. This is ok at 60hz but the insulation value of oiled
paper decreases with increasing frequency and is fairly low in the 100khz
Second,the secondary windings look like a VERY high impedance to
100khz so the high voltage high frequency hash that the winding is
exposed to distributes itself over a the first few hundred turns of the
winding helping to break down that paper. This is where the burn out
occured on the transformer I depotted. the first few outer layers.
Therefore, I made 2 8kv transformers by hand. The layers are
insulated with Kapton tape which is good for 7kv per mil and is a great
insulator at high frequencies. Also I installed a "shield" of copper
screen around each secondary (don't make a shorted turn here) to
capacitively couple the hash over a larger area of the secondaries.
With the ballasting resistance of 4ohms per xformer I figure
about 6kv each x2 = about 12kv operating voltage and no problems for ovr
a year of regular use.