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Twin Spark Gap coils out of phase

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StevenCaton

Fri Dec 05 2008, 06:52AM

Registered Member #1845 Joined: Fri Dec 05 2008, 05:38AM
Location: California
Posts: 211

I am going to build a twin solid state coil system eventually. In the meantime, I donated my old spark gap coil to my physics teacher, but he didn't need the transformer or the rotary gap, so I decided to use these items to make a twin spark gap coil system before I attempt a twin solid state system.

It will be powered by three 12/30 NST's in parallel. It will have a synchronous rotary gap at 60bps. The mmc bank consists of 45 .1 uf poly caps. The primary coils are made from brass weatherstrip. The two primaries will be in series, but their electrical connections will be opposites in order to provide the 180 degree phase relationship.

All I have left to do is the wiring, which won't take long, so first light will be withing the next two days.

I have some questions...
1. Is it important to keep the tank circuit wiring as short as possible. I know in a SSTC the bridge layout should be kept tight for low inductance, but is this very important in a spark gap system as well.
2. I will place breakout points on each toroid. Should I just use thick copper strips sharpened to a point, or should I take the time to make the points out of stainless steel or tungsten. I just don't want the sharp tip to melt off. I don't think the copper point will melt away, though.
3. Any guesses as to how long the sparks will be between coils.

GeordieBoy

Fri Dec 05 2008, 12:32PM

Registered Member #1232 Joined: Wed Jan 16 2008, 10:53PM
Location: Doon tha Toon!
Posts: 881

> a synchronous rotary gap at 60bps

60BPS !?!?! If it really is 60bps it will likely cause all sorts of problems with the NSTs. Aim for 120bps or 240bps in countries where the leccy is 60Hz flavour. Use a good safety gap across the RSG.

> 1. Is it important to keep the tank circuit wiring as short as possible

Try to keep all the connections close together. Big loops that enclose lots of area add leakage inductance, effectively reducing coupling to your secondary coils. I would put all the workings under one coil, and use two parallel copper pipes spaced 2" apart to carry the primary current to- and from- the other primary coil. Keeping the pipes close together minimises the enclosed area and minimises the leakage inductance.

> 2. I will place breakout points on each toroid.

You could use telescopic antennas from old cordless phones or radios for the breakout points. Adjusting the length of each independently allows you to compensate for the mismatch in the two resonant frequencies of the secondaries due to surroundings etc.

> 3. Any guesses as to how long the sparks will be between coils.

6ft should be achievable.

-Richie,

StevenCaton

Fri Dec 05 2008, 07:29PM

Registered Member #1845 Joined: Fri Dec 05 2008, 05:38AM
Location: California
Posts: 211

My rotary gap spins at 1800 rpm and lets the caps discharge twice during each revolution. This gives 60bps, But since you think sixty breaks per second is too low, I could modify it and add more terminals to do 120bps. It wouldn't be all that hard so I will do it. Why is 60bps inferior to say, 120 or 240?

I will use the copper pipes to carry the primary current between coils.

Thanks Richie

Dr. Dark Current

Fri Dec 05 2008, 09:21PM

Registered Member #152 Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384

SteveC wrote ...

Why is 60bps inferior to say, 120 or 240?

Because it loads the transformer only in positive /or negative/ halfwaves, this saturates its core and causes it to draw huge currents from the mains.

StevenCaton

Fri Dec 05 2008, 11:54PM

Registered Member #1845 Joined: Fri Dec 05 2008, 05:38AM
Location: California
Posts: 211

You could use telescopic antennas from old cordless phones or radios for the breakout points. Adjusting the length of each independently allows you to compensate for the mismatch in the two resonant frequencies of the secondaries due to surroundings etc.

I also have some questions about this. What happens in a twin system such as this when there is a discrepancy in the resonant frequencies. For example, what if one secondary coil, was three inches longer than the other, or what if one toroid was slightly larger. Could it throw the system out of balance and make one coil spark longer than the other?

Anon01

Sat Dec 06 2008, 12:06AM

Registered Member #1589 Joined: Sun Jul 13 2008, 06:40PM
Location:
Posts: 70

I would highly suggest safety gap, and terry filter appropriately sized.

It would be a disappointment/waste to see those NSTs die like that.

Arcstarter

Sat Dec 06 2008, 12:30AM

Registered Member #1225 Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253

SteveC wrote ...

You could use telescopic antennas from old cordless phones or radios for the breakout points. Adjusting the length of each independently allows you to compensate for the mismatch in the two resonant frequencies of the secondaries due to surroundings etc.

It would make a difference in spark length if you tuned both at the same turn, yes. But you will need to tune independently, as no two coils are exactly the same, whether it is the toroid or the length, difference in wire gauge(no wire is exactly the same) or difference in form diameter(heat changes diameter).

Tune each as needed, and when max spark length is achieved on both, they would probably be very close to the same spark length. If one coil will not tune as good as the other or just doesn't have as large a spark length, you might just have to detune a little bit, so that one is not throwing sparks bigger than the other.

Just my 2 cents(seem to hear that alot on this forum these days, figured i might try it out) :P.

StevenCaton

Mon Dec 08 2008, 05:34AM

Registered Member #1845 Joined: Fri Dec 05 2008, 05:38AM
Location: California
Posts: 211

Heres a picture of the coil base with the works underneath it. I redid the spark gap to provide 120bps, instead of 60bps. I have also finished the primary current send and return lines to the other coil. I used 1/2 inch copper pipe. Its all finished and I'm basically ready to turn it on. But It'll probably be a week until I can actually turn this thing on because I discovered one of the NST's was dead when I was setting the safety gap.

From breakout point to breakout point, the distance is 6ft. If it can't do 6, then the cool thing is that I can stretch out the antennas (I am using telescoping antennas for breakout point) to shorten the gap. (thanks for the idea richie)
C:\Documents and Settings\Robert Caton\My Documents\My Pictures\coil base.jpg

StevenCaton

Mon Dec 08 2008, 05:36AM

Registered Member #1845 Joined: Fri Dec 05 2008, 05:38AM
Location: California
Posts: 211

oops, pic didn't show, here it is
C:\Documents and Settings\Robert Caton\My Documents\My Pictures\coil base.jpg

StevenCaton

Wed Dec 24 2008, 09:08PM

Registered Member #1845 Joined: Fri Dec 05 2008, 05:38AM
Location: California
Posts: 211

Visit My Site

Here is a video of the system!

I'll have to move the coils an inch closer later, because there are only a couple solid strikes between coils.

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