Sciencemadness Discussion Board

High voltage sparkgap

Belowzero - 9-8-2021 at 04:56

Hello SM,

For a project I am working on I have a neontransformer and a spark gap.
Sometimes the arc collapses and it does not form again by itself, I need to cut the power and restart it to create the arc, obviously I don't want to do this by hand.

So I would like to find a way of preventing or automating this.

Would it be possible to use a capacitor to provide more juice to create the arc? (similar to fluorescent light starting?)
How would such a circuit be called?
Or am I completely on the wrong track?


Forgive my stupidity, I guess I do not know in which direction to look..
Any suggestion would appreciated!

wg48temp9 - 9-8-2021 at 06:03

Perhaps if you give more info some one may be able to help.

Are the only circuit elements the neon sign transformer and the spark gap?

Is the neon sign transformer the old type, large and heavy with two ceramic insulators or the modern smaller type usually called electronic transformer.

MarkoMiletic - 9-8-2021 at 06:33

Cold-cathode devices typically use a complex high-voltage power supply with some mechanism for limiting current. Although creating the initial space charge and the first arc of current through the tube may require a very high voltage, once the tube begins to heat up, the electrical resistance drops, thus increasing the electric current through the lamp. To offset this effect and maintain normal operation, the supply voltage is gradually lowered. In the case of tubes with an ionizing gas, the gas can become a very hot plasma, and electrical resistance is greatly reduced. If operated from a simple power supply without current limiting, this reduction in resistance would lead to damage to the power supply and overheating of the tube electrodes. Cold cathode - Wikipedia

Belowzero - 9-8-2021 at 07:30

Quote: Originally posted by wg48temp9  
Perhaps if you give more info some one may be able to help.

Are the only circuit elements the neon sign transformer and the spark gap?

Is the neon sign transformer the old type, large and heavy with two ceramic insulators or the modern smaller type usually called electronic transformer.


I think this would qualify as a modern transformer.

Well the circuit is as plain as it gets, its basically 2 copper tubes which are connected to the HV output of the trafo.

macckone - 9-8-2021 at 10:19

It sounds like what you have is some variant of jacob's ladder/birkeland-eyde reactor.

The smaller lower gap needs to be sufficiently short that it can be bridged by the arc on startup.

There is something called a gabriel electrode which can help with this.
It is an intermediate, high resistance electrode that will charge to the breakdown voltage and then stop conducting at an apprciable rate.
It was invented for just this purpose.
You will have to add a high voltage resistor of the appropriate resistance.

Alternatively, the transformer you are using may have a safety that prevents it from forming the arc on startup without power down.

Metallophile - 9-8-2021 at 10:52

Either reduce the gap so the arc does not extinguish, or add a switch on the low voltage side to allow power cycling. I think a capacitor on the output would probably just blow up real good.

wg48temp9 - 9-8-2021 at 12:14

Quote: Originally posted by Belowzero  
Quote: Originally posted by wg48temp9  
Perhaps if you give more info some one may be able to help.

Are the only circuit elements the neon sign transformer and the spark gap?

Is the neon sign transformer the old type, large and heavy with two ceramic insulators or the modern smaller type usually called electronic transformer.


I think this would qualify as a modern transformer.

PS: Can anyone tell me what happened to the thread about cats licking themselves clean ?

Well the circuit is as plain as it gets, its basically 2 copper tubes which are connected to the HV output of the trafo.



It sounds like you have an electronic neon sign transformer which have automatic protection against high currents or high voltages. If it detects either condition the electronic transformer turns off and remains off until the mains input is turned off and then back on.

So you probably need to place a resistor in series with the spark gap to reduce the current to be within the working range of the electronic transformer.

Your transformer probably looks something like :

elecneon.JPG - 20kB

The old version (shown below) have a built in inductive ballast that limits the current to no more than the transformer rating when driving a spark gap. However the transformers are not designed to drive spark gaps and can fail in minutes when doing so. Ideally you need a resister capacitor filter between transformer and the spark gap.

oldneon.JPG - 19kB

[Edited on 8/9/2021 by wg48temp9]

Belowzero - 10-8-2021 at 03:46

Thanks everyone!


I really like the suggestion for a gabriel electrode, I'll try to find some HV resistors somewhere.


My transformer looks something like this:
http://npalighting.com/wp-content/uploads/2013/10/FART-trans...
Quote:


So you probably need to place a resistor in series with the spark gap to reduce the current to be within the working range of the electronic transformer.


I'll try and see what that does.



[Edited on 10-8-2021 by Belowzero]

macckone - 10-8-2021 at 08:44

That transformer is definitely going to have some safety features.
It is likely current and temperature limited.
When arcing it is likely pulling too much current and heating up.

Is it outputting pulse dc or ac?
There are different solutions for each one.

A resistor will help but HV systems with resistors can be tricky.

wg48temp9 - 10-8-2021 at 11:37

Quote: Originally posted by macckone  
That transformer is definitely going to have some safety features.
It is likely current and temperature limited.
When arcing it is likely pulling too much current and heating up.

Is it outputting pulse dc or ac?
There are different solutions for each one.

A resistor will help but HV systems with resistors can be tricky.


If its designed to drive a neon sign tube it almost has to be AC.

Yes the resistor will have to be rated for the voltage and power dissipation. either one big and long one or a string of smaller ones.

Mateo_swe - 12-7-2022 at 13:42

Even that is a pretty modern transformer its based on the old types and i doubt there is any safety features on it and it has no ballast
It is a dual coil transformer, something like 3.7kV AC x 2 with a center tap at 0v, 50Hz (or 60Hz if in US).
So you got something like 7,4kV end to end.
The transformer is resin filled (heavy) and used for driving neon signs, it handles short circuit without turning off (no safety features).
Its a common model, i have a few myself and mine are 2 x 3.7kV, 60mA but there are other voltage and current models.
I used one of mine to drive a tesla coil long long ago.
I somehow managed to turn on our house burglar alarm and trigger it with my tesla coil so the siren began screaming.
I have no idea how that is possible but it happened, strange indeed.
Huge generated electrostatic from the teslacoil i guess.