FAQ - Demo fusor - why do I want a neon transformer?

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Richard Hull
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FAQ - Demo fusor - why do I want a neon transformer?

Post by Richard Hull » Mon Jul 29, 2013 6:11 pm

This FAQ will, hopefully, get a point across on the issue of a real neon transformer versus a modern, smaller, cheaper, electronic replacement.

The Neon Transformer 1920-2010.........

Neon tubing and lighting began in the 1920's as a going thing. Elaborate signage was constructed in this often artistic, but sometimes garish medium early on. Hundreds of feet of noodled up tubing could be involved in just one sign. Neon lighting involves plasma physics at its core and several laws and codes within this science make certain demands on getting the medium to start and run reliably for years on end.

Basically, it requires a lot of voltage, (thousands of volts), to start neon signage. This voltage varies based on the overall length of the particular length of tubing to be started. This is because a lot of gas must be ionized via electrical breakdown between two distant conductors within the gas environment. (The longer the tube, the more voltage is needed to start the tube.

Once the gas ionizes and starts to glow, the resistance of the now conductive gas, (plasma), falls to near zero. If the starting voltage were to be left constant, the tube would explode as many amps of current and thousands of watts would try to flow in the massive load just created. The normal current needed for bright neon tubing of normal diameter is only about 30 ma ( thirty thousandths part of one amp)

The delima facing the early 1920's neon industry was how to cheaply, establish a 15,000 volt transformer output, yet, once a large load appeared after starting, have the voltage plunge to a much lower sustaining voltage, (~300-600 volts), to limit the current in the tube to about 30 ma.

As there was no real electronic solution at that time, they were forced to use a clever but inefficient transformer design called a "magnetically shunted transformer" this involved a "leakage" path for the core's magnetic flux which would not support or shunt away high flux levels via a high reluctance magnetic shunt within the core of the transformer. Thus, when first turned on at no load, the windings would supply thousands of volts to the tube contact ends, forcing the tube to light. As the current instantly leaped to huge values, the core's flux would be shunted away from the windings and the output voltage would plunge due to the high resitance of the secondary wiring, (ballasting), and flux shunting ,(leakage), would limit the current to a point where the tube would draw a specificed amount of current. All of this required careful initial design. Such designs were quickly mastered and the neon transfomrer which weighed from 10-60 lbs became a common everyday accessory within the business.

Short signs like "Open", "Eat at Joe's", etc., only needed about 3000-5000 volts to start and could be made much small and cheaper. So several neon transformer "stock"voltages were offered depending on the length of tube in the signage. (3kv, 4kv, 5kv, 6kv, 7.5kv, 9kv, 12 kv,15kv) All were 30ma max current transformers. However, there were 60ma and very rare 120ma designs within the voltages specified for larger diameter tubing and special neon applications. Such transformers are still being made but no longer dominate the market

The modern electronic, high frequency, switching neon power supply.......... ~1995 to date

With the advent of modern electronic, high efficiency, high frequency power supplies, the classic iron neon transformer was doomed. Modern iron Neon transformer's list price is on the order of $100.00 - $800.00. A modern switcher in the same capability range is from $30.00 to $150.00 for the same ultimate delivery.

Why not use one of these lighter, cheaper and more efficient systems?? Well, it has to do with the manufacturing philosophy and price point. 90% of all the modern neon switchers encountered on e-bay and the like are taken from "open" signs that glut the market. These can't be compared to an equivalent iron core unit. Why?

1 The iron core unit can, when connected to a variac, can supply 0-120 volts to the primary and yield zero to the full kilovolt rating on its nameplate. The cheap switchers cannot do this as they rely on a certain minimum input voltage before their electronics kick in or even start to work and, as such, have no full variabilty which is highly desirable in demo fusor work and experimentation.

2. The switchers can't sustain much real current at their high voltage ratings. Some units can't even supply 1 ma at full voltage. This is a design decision to reach a sales price point as the things are designed for one mission only and whatever it takes to do the job and nothing more is the corporate philosophy. This $15.95 neon supply will light a 3 foot "open" sign and nothing else. Their is no reserve capacity or transferable capability as was found in the non-electronic iron core units of yesteryear.

3. Their is no usable "ramp" in the voltage vs. current curve on the electronic units. The instant current is sensed the unit drops to a sustain voltage, all easily designed in a modern all electronic design. No wasted power or energy and cheap too!

The above explains where few if any modern electronic neon supplies are found to be suitable in a full range, as purchased, solution for use in a demonstration fusor. Avoid issues and wasted money. Avoid modern, all electronic, inexpensive neon supplies.

Buy and use only real iron core neon transformers. Buy them surplus if possible. Local neon sign shops often have many used units at tolerable prices.

Remember, a neon transformer is for a demo fusor. It is NOT normally suitable for a real, fusing, neutron producing fusor.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
Retired now...Doing only what I want and not what I should...every day is a saturday.

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Re: Demo fusor - why do I want a neon transformer?

Post by David Swan » Tue Jul 30, 2013 9:00 am

Thanks Richard, this has saved me from a potentially expensive mistake.

Although I was aware that senior members reckoned the electronic types were unsuitable from reading forum posts I was "taking it as read", whilst also wondering if I *could* make it work.

But now I understand the why, I'll start looking for a real iron-and-copper transformer.

Thanks again

Dave Nicholls
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Re: FAQ - Demo fusor - why do I want a neon transformer?

Post by Dave Nicholls » Tue Dec 17, 2013 11:26 pm

Well that's a shame!

I bought a Neon Power Supply to replace the old NST which broke when I tried to bring it back from abroad. I hoped to use it on a Tesla Coil, and then found out that it wouldn't work. So it's been sitting in the cupboard ever since. I thought a demo fusor would be a great project to finally put it to use! Oh well...

I have a ZVS, and so I will try with this instead.

Thanks Richard. Wealth of info in here, and I'm still getting to grips with it all.

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Re: FAQ - Demo fusor - why do I want a neon transformer?

Post by Andrew Haynes » Wed Dec 18, 2013 12:26 am

I was planning on running my reactor with a neon 6-12month plainng and don't see a problem, but could a fuser work if you have the load matched to the rated specs. if its a 30ma neon a wouldn't a 5Mohm keep the voltage at the top of a neons output.
You would have to have small grids spacing or a resistor in line.

Thoughts?
Andrew Haynes

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Richard Hull
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Re: FAQ - Demo fusor - why do I want a neon transformer?

Post by Richard Hull » Wed Dec 18, 2013 5:26 pm

The rated specs of all neon transformers as a paired voltage and current is a lie!
Read the FAQs and the file forums. For the thousandth time .........

viewtopic.php?f=19&t=7945


Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
Retired now...Doing only what I want and not what I should...every day is a saturday.

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