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NEON AND SHUNTS? HELP PLEASE!!




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From:  Bert Hickman [SMTP:bert.hickman-at-aquila-dot-com]
Sent:  Saturday, January 31, 1998 4:37 PM
To:  Tesla List
Subject:  Re: NEON AND SHUNTS? HELP PLEASE!!

Tesla List wrote:
> 
> ----------
> From:  Zuma [SMTP:mwise-at-ns.sosis-dot-com]
> Sent:  Saturday, January 31, 1998 12:38 AM
> To:  Tesla List
> Subject:  Re: NEON AND SHUNTS? HELP PLEASE!!
> 
> Tesla List wrote:
> >
> > ----------
> > 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.
> > >
> > > ADVICE IS NEEDED, PLEASE
> > >
> > > Chris
> >
> > 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
> > doorstops.
> >
> > Hope this helps, and safe coilin' to you, Chris!
> >
> > -- Bert --
> I have a question concerning this. I tried this and according to the
> meter it was reading a max of 6.0 volts. Does that seem right? I used
> the same size of resistor you suggested to come up with this 6.0v.
> I also wanted to ask if not running full 120volts through the primary
> affect the ma on the secondaries? The plug I used is running at has
> a fluxuating voltage of 113-115volts according to the meter. Could this
> be why I am not even getting more than 60ma out of my tranny? Remember
> I removed 2 shunts from each of the sets of 23, so my line of thinking
> says I should have increased the ma at least a little. But no such luck.
> do you think removing more would help or would that possibly destroy
> my primary or even the whole transformer?
> 
> Thanks
> Chris

Chris,

Neons are specified at nominal voltage in - for most neons this is 120
VAC. Try repeating the output current measurement while using a variac
on a 0-140 VAC setting to "step up" the line voltage to 120 VAC nominal
to the input of the neon. If your incoming line voltage is significantly
below this, more current will be drawn by the primary which may cause it
to run a bit hotter. A new 60 mA transformer actually delivers a bit
more or less than 60 mA - it is nominally 60 mA +/- 10% or more. You
should be able to "tweak" the shunting to get 80-85 mA at 120 VAC in
with no problems. And, you can even push it a bit more by immersing it
in an oil bath as long as you let the heat that builds inside the
windings dissipate by keeping run-times reasonably short, with cool-down
periods in between. BTW, 30 mA transformers are not quite as forgiving
due to the significantly smaller wire used in the secondary windings...

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

-- Bert --