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Re: Help required - ignition coil Tesla

Original poster: Frank <fxrays@xxxxxxxxxx>

Hi James,
Using spark coils will never get you a big spark.
You need some current to excite the coil and automotive coils will just not supply what is needed to peak the coil.

I would suggest you find a 4 to 6 KV @ 30 ma neon sign transformer or an oil fired furnace ignition transformer. and try that.

You are probably putting in an estimated 40 watts max into the coil and you are going to get the result you have. By using a NST, you will be putting in approx 4 times the power with the 4KV and approx 6 times with a 6KV one.

Use a  capacity  around 20,000 pf or 0.02 mfd  with the transformers.

For the ignition coils you are using, I would halve the capacity you have to a value around 0.002 mfd. You will still not get a big spark unless you increase the current and car coils will be unable to supply that.


At 09:10 PM 1/29/2007 -0700, you wrote:
Original poster: "James Howells" <james@xxxxxxxxxxxxxxxxxxxxxxx>

I have spent every day since Jan1 working on my tesla and can not get more than a 1" spark no matter what I do

To save my sanity - some help is requested - I WANT TO GET BIGGER SPARKS!
Power supply:- Twin Auto Ignition coils - 555 interrupter through two power transistors. A separate oscillator supply to main 12v battery-ball point pen case chokes - works well

Spark gap :- 6 mm copper tube fixed end to end but gap adjustable - best setting seems to be 0.1" Primary : 4 series 390 pF 15kv caps , and 3 in series 390pf 15kv caps ( should be 4 of each, but leg fell off one cap and no replacement yet) the three strings are in parallel
{4 x 390}
{4 x390}
{3x 390}

Primary coil wound on 4.3" plastic soil pipe ( sewer pipe) with .048" enamelled wire Turns 18 at present but was 30 and reduced it and tested one turn at a time down to 18 turns

Secondary: wound on 2.64" dia white ( abs?) plumbing waste pipe approx 450 turns of .019" enamelled wire to a height of 10.25 "

Various toroid top loads have been tried ... and non , which works best!

The present spark at the Tesla is about 1" which is about 20% of what I expected
I have not been able to improve on this - PLEASE HELP!

I built a Tesla Coil Tester to match the resonant frequency of the coils ( it's a 555 and two LED job, and I think it works like the grid dip oscillator Thank one needed to have here for compliance with our Ham licence).
The coils do show oscillation at the same point on this home made instrument

Originally the tester had a range too high for my coils so, I had to double the oscillator capacitor inside the tester - and as a consequence lost even the crude calibration that was there to give me a quantative reading. This said, I think both coils resonate at about 800 kHz, and this is about the area my calculation show also.

How close do I have to be with the frequency match ? Is it exact or nothing or is some mismatch possible but with reduced spark length?

Thanks in anticipation of your replies

James Howells

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