From:  Bert Hickman [SMTP:bert.hickman-at-aquila-dot-com]
Sent:  Thursday, January 29, 1998 8:34 AM
To:  Tesla List
Subject:  Re: NEON AND SHUNTS?

Tesla List wrote:
> ----------
> From:  Zuma [SMTP:mwise-at-ns.sosis-dot-com]
> Sent:  Wednesday, January 28, 1998 8:40 PM
> To:  tesla-at-pupman-dot-com
> Subject:  NEON AND SHUNTS?
> I posted an e-mail a while back on my 12kv-at-60ma neon that I unpotted and
> modified. I stepped up the insulation around the primary and both of the
> secondaries. I also removed some shunts. The tranny had 4 sets of 23
> shunts, I removed 2 shunts from each set. That leaving 4 sets of 21
> shunts. In my post I stated that when I run the tranny the primary
> heats up. It gets hot but not so hot it burns when you touch it.
> I am wondering if anyone might have an idea if this is going to be ok
> and would also like to know what kind of current this thing might be
> giving off now? I was told that it is probably just heating from the
> extra current it pushing out, which makes sense because I noticed that
> after a while the power cord began to heat up. I don't think it is
> shorting at the primary because I had a problem once with a 15kv-at-30ma
> neon that smoked within a minute because it was shorted.
> Chris


Removing shunts allows more primary magnetic flux to engauge the
secondary, increasing the secondary's short circuit current. Since
there's no free lunch (on Chip's List as least :^)), this also increases
the amount of primary current drawn. A shorted primary would most likely
cause severe overheating or your line circuit breaker to pop. 

If you want to measure your tranny's new short circuit current,
CAREFULLY connect a 100 ohm 1 watt resistor directly across your
transformer's output bushings and measure the output voltage developed
across the resistor with a cheap battery-powered VOM or DVM. Hook
everything up solidly, and ramp the power up with a variac... and STAY
AWAY from all of the HV side wiring and the meter while making the
measurement. Look for any signs of arcing while ramping up the voltage,
and fix the problem. Set the variac to output 120 VAC.

The low valued resistor will force the transformer to go current
limiting mode, and the AC RMS voltage you measure will allow you to
measure the value. Let's assume you measure 8.5 volts:

   Ineon = V/R = 8.5/100 = 85 mA

This approach also comes in very handy when you get "warranty return"
transformers, since these often have missing faceplates - the faceplates
are often removed and sent back to the neon sign equipment distributor
for credit, saving the hassle of sending back a big pile of 40 pound

Hope this helps, and safe coilin' to you, Chris!

-- Bert --