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4hv.org :: Forums :: Electromagnetic Projectile Accelerators
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Triggered spark gap success

Author Post
Sun May 03 2015, 08:48AM Print View
Joined: Thu Mar 22 2007, 07:40PM
Location: Northern Finland, Rovaniemi
Posts: 623
Some time ago i found this post and decided to give it a go myself:

I don't have any construction pictures but here is one of the higher energy test shots we did. Bank was charged to 1380V and discharged through soda can. After firing bank voltage was reading about 150V so energy released was about 29.5kJ

We performed several, maybe 20 shots at different energy levels. What i really like about this gap design is that it fires at any main storage capacitor voltage. Even all the way down to like 20V. It fires instantly, and i can use very safe gap spacing. Triggering is simply done by turning on the 12kV power supply, which is just rectified NST and BOOM.

Here are some aftermath photos from last night (the intensity of the main gap arc blast is insane!) Main current path electrodes are made from tungsten copper alloy (70% tungsten, 30% copper) and they are holding up very well. I can still see some machining marks at the ends. Trigger gap electrode is plain old brass screw.

Even though the trigger electrode is not in the main current path it gets hit by the arc blast so badly i will move it entirely away from the main gap area. Also next version will have different support structure and some sort of casing to countain the noise and light.
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Sun Jun 14 2015, 02:01AM
Registered Member #54278
Joined: Sat Jan 17 2015, 04:42AM
Location: Amite, La.
Posts: 285
I find this trigger very interesting--20v--GREAT! I need a good triggered gap for a quarter-shrinker. I would like to try this one. Is your gap exactly as in the first schematic?

Also, I was thinking about an automotive ignition coil + SCR...much lighter than NST-based. Would that work here?

I use a variac + NST + diode string that looks much like this for my HV cap charger.
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Sun Jun 14 2015, 10:57AM
Registered Member #11591
Joined: Wed Mar 20 2013, 08:20PM
Location: UK
Posts: 428
I have a similar TSG, made out of an old Tesla coil spark gap with an extra electrode holder glued onto it. I designed it to be used for 5/10kV pulse discharge oil filled caps, but it should be good for electrolytics.
I used a small flyback transformer and a Mazzilli driver to trigger the gap. The hot arc gives a very repeatable firing that, I think, would be even better at lower voltages and a smaller gap distance.
Ear protection is necessary!
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Ash Small
Sun Jun 14 2015, 01:41PM
Registered Member #3414
Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4118
What diode did you use, Kizmo?
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Thu Jun 18 2015, 04:57PM
Registered Member #54278
Joined: Sat Jan 17 2015, 04:42AM
Location: Amite, La.
Posts: 285
Since the automotive coil has worked for me with virtually 100% success (when used with an SCR) and such simple circuit, I was wondering if there were other 'types' of ignition coils anyone else has used...i.e. motorcycle, four-wheeler, etc. I am interested in smaller and lighter.

Also, on the other end of the spectrum, where would I find a "monster" version ignition coil? (I have some REALLY tough-to-trigger laser flashlamps that have four to five foot arc lengths @ one to two cm bore! I need the "portable" 6VDC to 24VDC drive power.

This may also be useful in a homemade TSG designed for 10kVA, which uses two 1-3/4" brass spheres with adjustable gap. The trigger is simply a 4-40 (maybe a bit larger) electrode with a shiny sharp point at the end. It enters from the top. The trigger gap is threaded and placed between the similarly threaded main electrodes (1/4" brass screws) so that the trigger's point may be set ay any distance from either sphere at any height. It is all encased in heavy (1/2" lexan--about 3" x 5", 3" high). I have never used it yet. Originally for a coin-shrinker... Triggering is via an LED at 'my' end of a 6m sheathed optical fiber.

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Fri Mar 11 2016, 08:08AM
Registered Member #54872
Joined: Fri Apr 17 2015, 06:33AM
Posts: 24
what are the rating of diodes you used kizmo ???
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Fri Mar 11 2016, 08:43PM
Joined: Thu Mar 22 2007, 07:40PM
Location: Northern Finland, Rovaniemi
Posts: 623
rajheman wrote ...

what are the rating of diodes you used kizmo ???

The anti parallel diode of the main capacitor?

As large as it can be :D I think 1600V 9500A pulse. Brick style diode
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