Neon Sign Transformers Protection Circuit  

Neon Sign Transformers (NSTs) aren't really designed for the abuse that Tesla Coil service dishes out.  
You need to take 2 steps to ensure that you NSTs have a better chance of survival.  

(1) Safety Gaps
The safety gaps should be set so they almost fire when the transformer is at maximum V(out).

(2) Low Pass Filters
There are several ways to build these.  Some people like to use an LC circuit, but the most failsafe is a simple RC circuit.  Terry Fritz has some excellent filter resources on his web site.  I had good results running a bank of (4) NSTs on my coil with absolutely no protection for months.  Other people routinely blow NSTs with lots of filtering.  Guess you never know...  Check out Terry's Page

  http://www.peakpeak.com/~terryf/tesla/experiments/rcfilter/rcfilter.html

One other thing, don't use Terry's recommended filter with the values that he calls out for anything larger than a 12/60.  Larger PSUs will dissipate far too much energy in the filter resistors.

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