NST

[Jun]

Hi everyone. This is my first time posting to this forum. I am currently designing NST RSGTC.
I was originally planning to make Asynchronous spark gap, but came to this website that I would like to clarify.
I've read Terry Blake's page saying that compared to synchronous spark gap tesla coil, Asynchronous spark gap has more advantages and allow the user to easily adjust the RPM, BPS and etc... I was convinced to make Asynchronous spark gap with angle grinder and variac.
However, I read this website (http://www.teslacoildesign.com/construction.html) saying that NST should only be used with static gap or synchronised motor.
Why is this? Is there any thing wrong with using Asynchronous spark gap? or Is this some sort of mistake the uploader made?
Thanks.
Jun

[profdc9]

I made an asynchronous spark gap using an angle grinder, stainless steel screws as spark gap points, and G10 laminate for the wheel holding the screws.  I used two microwave oven transformers in series with a voltage doubler to get 12 kV peak rather than a NST.  I will say it is very tricky to balance a wheel rotating at high speeds (10,000 RPM) and maintaining a small enough gap for reliable triggering  (1-2 mm) between the rotating wheel points and the stationary points.  Eliminating all of the imbalance is nearly impossible and you will have to secure it down so that the spark gap doesn't "walk." You definitely need to build a sturdy enclosure around it in case it flies apart, and you might destroy an angle grinder's bearings before you get one to work correctly.  But it can be done.  I would say that a DRSSTC in some ways is much easier to build for this reason.

[Jun]

Hey profdc9. Thanks for spending your precious time answering this question. I was looking for a different answer. My question may not have been clear.

The website claimed that the Neon sign transformer should be only used with static or Synchronous spark gap.
And I think it's okay to use Asynchronous motor.

[davekni]

Hopefully someone with direct experience will answer too.  A high spark frequencies I'd expect few issues.  At lower spark frequencies, there could be problems when the spark timing is close to line frequency.  If sparks hit only the positive half-cycles for example, there would be DC current draw on the transformer, causing the iron to saturate.  At really low spark frequencies, there could possibly be an issue if the MMC capacitance and transformer leakage inductance happen to resonate at the line frequency.  I think only larger-than-normal MMC capacitance could cause such a problem.

[MRMILSTAR]

I think that your best bet to get an authoritative answer is to post your question to the TCML at:

https://www.pupman.com/

This is where you will find the most expertise regarding Tesla coils. I have seen this question answered before on there but I can't remember the answer. The answer is probably in the archives.

[Jun]

I think asynchronous spark gap should be fine because I've seen few tesla coil that uses line frequency with asynchronous motor. I would definitely make sure that the spark gap fires consistently.  Thanks for answering!