which variety of neon sign transformer for tesla coil

Thread Starter

pager48

Joined Nov 25, 2018
161
It appears every UL listed NST has ground fault protection rendering them useless for tesla coils.
 
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SLK001

Joined Nov 29, 2011
1,548
Because a Neon power supply will shut down if a fault is detected, you'll have to build your own HV supply using an old TV flyback transformer. Many schematics exist for those.

But Tesla coils don't use a HV supply. It is a HV transformer by itself. You just supply high frequency pulses to the primary.
 

DbLoud120

Joined May 26, 2014
82
The primary is actually heavy gauge wire.

It doesn't really generate a high enough voltage that it will reach the primary.

The transformer has a grounded center tap, so for safety, I only used one high voltage lead and ground for the spark gap, which reduced my available voltage to half the transformer's rating.

It will generate streamers of about 4 to 6 inches, but the high voltage is not harmful, due to the high frequency, unless a spark makes direct contact with skin, it will make a small burn where it makes contact.

I don't operate it long enough to get hot as large amounts of ozone are generated.

I built this device over 30 years ago. I salvaged my transformer from a business that was being renovated so I don't really have a part number.

The purpose of my comments was to inform others what is involved in making a Tesla coil.

I would try Ebay for a transformer. Contact some of the sellers to locate one that is not ground fault compliant. Also, check the article I attached for more tips.

In this photo I am holding a small CB antenna directly by the end, I feel only a light tingling sensation.
 

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DbLoud120

Joined May 26, 2014
82
Actually, the Oudin coil is considered an autotransformer.

Oudin_coil_circuit_-_early_type.svg.png
My device has one end of the secondary connected to ground and the other end is floating.
The only difference between my Tesla coil and the conventional circuit is one end of my primary is at ground potential for safety reasons Tesla_coil_circuit.svg.png
Images are from wikipedia.
 

DbLoud120

Joined May 26, 2014
82
Please refer to page 20 of attachment in post #8.

There is a radio frequency choke in the spark gap circuit to suppress EMI.
A .005 µf capacitor is used to control the timing of the spark gap depending on the distance between the gap electrodes.
 

DbLoud120

Joined May 26, 2014
82
What bands do spark gaps typically emit?

I dont want to use a filter which will impede resonant cap current.
The resonant frequency of the typical Tesla coil is low radio frequency range, depending on individual characteristics.
A spark gap generates wideband radio interference.

A radio frequency choke only attenuates radio frequency voltages, it does little to reduce the passage of the 60 Hz ac voltage from the transformer supplying the spark gap.
 

DbLoud120

Joined May 26, 2014
82
I have never used ferrite beads for high voltage such as this. I wouldn't know how many to use or how to place them.

Maybe someone else on here might be able to advise you.
 

MisterBill2

Joined Jan 23, 2018
11,624
There is an entirely different variety of Tesla coil that uses an oscillator to drive the primary instead of a spark gap and high voltage source. They are quite a bit more complex but they can be more powerful and they generate a lot less broadband radiated noise. The oscillator circuits vary from those using old-style transmitting tubes to those using FET power transistors.
The only one that I ever actually touched was built by a junior-high classmate and the high voltage source was an old model"T" spark coil. So there is another option.
Present day neon sign supplies are amazing devices, I have one that lists the input power as 75 watts and the output power as 12000 volts at 20 Ma, which by my math is 240 watts output.
 

MisterBill2

Joined Jan 23, 2018
11,624
There is an entirely different variety of Tesla coil that uses an oscillator to drive the primary instead of a spark gap and high voltage source. They are quite a bit more complex but they can be more powerful and they generate a lot less broadband radiated noise. The oscillator circuits vary from those using old-style transmitting tubes to those using FET power transistors.
The only one that I ever actually touched was built by a junior-high classmate and the high voltage source was an old model"T" spark coil. So there is another option.
Present day neon sign supplies are amazing devices, I have one that lists the input power as 75 watts and the output power as 12000 volts at 20 Ma, which by my math is 240 watts output.
I acquired one of those "super efficient" neon sign drivers also, with similar specifications. It seems to function correctly, but I have not been able to verify the efficiency yet. Perhaps that should be in a thread, as we analyze those remarkable devices.
 

Reloadron

Joined Jan 15, 2015
6,543
Which variety of neon sign transformer for tesla coil

It appears every UL listed NST has ground fault protection rendering them useless for tesla coils.
While the posted electronics magazine article is pretty old my first experiments with Tesla Coils were around 1964 based on a few Popular Electronics articles titled Big TC and Lil' TC. The first used a Neon Sign Transformer having a 120 VAC primary and a 15 KV @ 30 mA secondary. That was the typical spark gap type but keep in mind the transformer was the old type and certainly lethal. Here is an example of an old one I have laying around.

Trans2.jpg

My 15 KV one had even larger insulators. The above is a 9.0 KV 30 mA unit. Anyway if you want a spark gap TC then you look for an old large heavy transformer like the one pictured.

The capacitors were home brew. Each capacitor consisted of three 12" X 12" panes of glass which sandwiched two 10" X 10" sheets of copper foil leaving tabs extending beyond the glass and all in wood frames. I am not 100% on those dimensions but the idea is the caps were home brew.

The Lil' TC was an oscillator using a vacuum tube driving an old TV flyback transformer, much the way the old horizontal output drove the flyback transformers on old TV sets. That TC offered a nice corona glow and taking the pointer out of an old kids compass and setting it on a sewing needle it would spin.

Anyway finding an old neon sign transformer is the hard part. The actual main coil was wound on a acrylic form and corona dope used. I have never seen a reprint of that old article. The Big TC was 250 KV give or take a few volts. :)

Ron
 
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