# Why isn't my medium spark gap Tesla coil working?

I am building a medium Tesla coil. I have checked all the parts of it and I cant find out why it isn't working. The hv transformer is a 12kv neon sign transformer. There is a gfci but it isn't tripping. For a spark gap, I'm using a single spark gap made of copper. I have tried putting them at various lengths away, but they still don't fire. The capacitors have a total capacitance of 14.1nF and are rated at 15kv. They are ceramic capacitors and current is flowing through them. The primary coil is 0.25 in copper tubing held with 0.25 inches between the windings, of which there are 7.5. I have tried using 1-7.5 turns, and that didn't make a difference. My secondary coil consists of 2032 turns of 32 awg wire around a 4 in inner diameter pvc pipe. I can verify that the 12kv is going through all of the places it is supposed to go through.

I have no idea why this isn't working, could anyone help me here?

## Comments

Best Answer 4 years ago

It is possible the spark gap is acting like an air gap capacitor do you have a fan blowing on the gap and how wide is the gap.

Answer 4 years ago

The spark gap had been tested at various distances, from 1/32 of an inch to 4 inches. I have been blowing on the gap, but nothing is changing.

Answer 4 years ago

What is the voltage across the gap?

Answer 4 years ago

The voltage could be at 12kv. I don't have a high voltage meter so I can't verify that.

Answer 4 years ago

If your meter goes up to 1000 volts, use the voltage divider rule and two resistors.

23 meg and a 1 meg ohm resistor in series across the points, then measure across the 1 meg and you should get 500 volts if the points are getting the right power.

Answer 4 years ago

That is a good idea, but I don't have some resistors like that. Of course I am relatively confident that 12kv is going through each point except the spark gap because I can disconnect at each point(except the park gap) and draw a spark at the about same distance as I would with just the NST.

I am starting to suspect that my capacitors may be faulty. I have been really busy with school so I have not been able to work on the tesla much, but I will check the capacitors at the nearest possible opportunity.

Answer 4 years ago

I chose in the mega ohms for the lower current.

It is basically the same thing as a 10x or a 20x probe for your oscilloscope. you can use smaller resistors but the current will be higher.

You might want to switch to AC polyester capacitors or microwave capacitors. Watch out for the microwave capacitors some of them have internal resistors and will just mess your tank circuit.

Answer 4 years ago

I have found that my capacitors were the problem. Apparently, all of the 10 capacitors I ordered were bad. I made a simple one with a cup wrapped in foil and at extremely small spark gap distances(less that 1/32 of an inch), the gap fired. I am either going to buy new caps or just make come beer bottle caps. Thanks for your help.

Answer 4 years ago

Go with the bottle caps their cool and they will mess with your friends heads.

Answer 4 years ago

I will, thanks.

Answer 4 years ago

Might help to add some detailed pictures...

A tesla system is dirt easy so no spark at all IMHO can only mean wrong connections or that the capacitor(s) are shorting out.

4 years ago

I figured out the problem. My capacitors were not working. They seem to have internal shorts so I will either buy new ones or make some beer bottle caps.

Answer 4 years ago

I will update to see if that actually solved anything or if something else is broken.

4 years ago

Show a photo of your build. What kind of insulators have you used.

4 years ago

Well a neon transformer is usually rated at 15 ma AC and definitely under 20 ma AC

running at 50 or 60 Hz. You don't mention the ballast value that you need for an AC Tesla

http://www.richieburnett.co.uk/resonant.html#reson...

Answer 4 years ago

The NST is rated for 50/60Hz. I'm using 60. The input is 120V, 2.5A and the output is 12kVRMS, 35mA. I have tested the ballast at values between 0.25mH and 16mH. I need around 7mH for it to work at the top efficiency.

I have tested the ballast at many vales, and even if I'm not running the circuit at optimal efficiency, it should produce some output. I am not getting anything out of my secondary and the gap isn't firing, no matter what distance I use for it.

Answer 4 years ago

Can you get arcs from the NST ? 12kV should jump 12mm or so

Answer 4 years ago

I am getting arks from the NST. It is around 12mm and I can stretch it to 30mm. the problem is that while the current is flowing through the system, it is not going across the spark gap.

Answer 4 years ago

+1

But the arcs are low line Fq which could stop your heart. You want the LC to resonate at RF Fq so that it can travel over the outside of your skin, thereby avoiding your heart muscle.