Newb Question, Do Tesla coils output AC voltage?

[bobfrancis1980]

It is my understanding from reading about tesla coils that they are an AC voltage source meaning they output AC current. Does this mean the sparks being emitted half the time being positive voltage sparks and half the time negative voltage sparks?

I was thinking of buying an off the shelf Tesla coil that was claimed to have a 250kV voltage output. I wanted to know if that meant it emitted sparks ranging from +250kV to -250kV or +125kV to -125kV. The guy emailed me back stating I was misunderstanding how tesla coils work.

I am familiar with CW and Marx voltage multipliers and that they can be configured to output positive or negative voltage depending on their configuration but of course they are DC and pulsed DC.

Thank you
Bob

[MRMILSTAR]

Tesla coils do indeed emit AC but it comes in bursts. For example, consider a coil that operates with a resonant frequency of 100 KHz and a break rate of 120 Hz. Each burst will consist of a damped sinusoid with a frequency of 100 KHz. This is the resonant frequency of the Tesla coil. There will be 120 such bursts per second. The burst rate isn't related to the resonant frequency. The sound that the Tesla coil emits is determined by the burst rate.

[bobfrancis1980]

Thank you, appreciate the response. The store emailed me today telling me the coil is no longer for sale at their store.

Good to know though when I look at other coils to buy. Further, if they are stating a specific voltage output it probably means the voltage they quote is the voltage level reached when emitting a positive burst and a when emitting a negative burst.

Thanks again

Bob

[MRMILSTAR]

Tesla coil output voltage is difficult to determine. Any numbers that you see quoted are probably just a wild guess. You can't use the conventional air breakdown voltage rule of thumb such as 1000 v/mm. This is because of the way that Tesla coils build a streamer. Its a series of bursts. Each burst leaves a plasma trail that the next burst follows. This allows a Tesla coil to generate a streamer which is much longer than the air breakdown number would suggest. The streamer gets longer until the input power capacity is met. JAVATC gives an estimated peak output voltage if you input the design parameters.