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AFSG: Alternating Fire Spark Gap

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brtaman

Mon Jun 29 2009, 11:42AM

Registered Member #2161 Joined: Fri Jun 05 2009, 03:36PM
Location:
Posts: 247

Hello,

Disclaimer: I have not been around these forums for long, so if this "innovation" is nothing new and has been done before I apologize, I did however come up with it on my own.

I have been enjoying building my TC for the past weeks and have had great fun. Yesterday I finished up my RSG and was somewhat disappointed with my results. So I started thinking of alternative methods of getting good quenching and after a little brainstorming I came up with the Alternating Fire Spark Gap (AFSG).

The principle is that two connected electrodes (primary and secondary) are spaced almost exactly the same distance from a single electrode, secondary a tiny bit farther, so that when the primary electrode over-heats and causes poor quenching the secondary takes over until the primary one cools of and continues. The results have been pretty good so far, but I believe I can get a lot more out of the system with fine tuning. (see beginning of the AFSG video for a visual)

Here is a video of a normal spark gap on my TC:

Here is a video of the AFSG running (can't get a good video of the spark gap switching, but it is happening ;)):

(Also sorry bout the resolution, damn phone keeps switching to a smaller resolution)

*** I am still tuning the AFSG, results should get better in time.

****Note due to the scientific process of this experiment nothing was changed in the system, even spark gap distances were kept at similair levels (as close as I could get them).

As you can see, there is quite a nice improvement in the output. What is your opinion on this Spark Gap? I think that it has pretty good potential for future use.

Thanks
brtaman

Fraggle

Mon Jun 29 2009, 01:39PM

Registered Member #1526 Joined: Mon Jun 09 2008, 12:56AM
Location: UK
Posts: 216

How are you persuading the arc to switch to the cold electrode? I`d expect it to prefer the hot one.

Diarrg

Mon Jun 29 2009, 02:02PM

Registered Member #1904 Joined: Sat Jan 03 2009, 02:40AM
Location: Pittsburgh
Posts: 14

Fraggle raises a good point. The entire deal with quenching is that the pathway is more ionized, and therefore the gap sparks sooner. Nothing should make the spark prefer the more difficult path. Now, a sucker or a blower would get rid of most of that pathlength, but I still see nothing that would make the spark prefer the cold electrode. Are cold objects more conductive? That would be the only possible explanation I could think of.

...

Mon Jun 29 2009, 07:06PM

Registered Member #56 Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445

Perhaps something could be done using a bimetalic strip? I would assume the gap is operating due to mechanical shifts, when the hot gap heats up it is somehow drifts away from the cold gap slightly (although how this happens I do not know). Another explination could be unrelated to heat, but that the gap gets eroded or corroded which makes it less likely to fire.

Arcstarter

Tue Jun 30 2009, 12:32AM

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

Are cold objects more conductive? That would be the only possible explanation I could think of.

The hotter something is, the more resistance. This should not be negligible I'd think. Not only that, that tiny tiny bit of resistance change would *not* change arcover distance at all. The gap size difference would overcome the resistance by hundreds or thousands of times.

brtaman

Tue Jun 30 2009, 09:01AM

Registered Member #2161 Joined: Fri Jun 05 2009, 03:36PM
Location:
Posts: 247

Thanks for the replies guys.

The whole idea is in its baby stage, will take some time and tuning to get perfected, if ever.

The thing that I perhaps didn't make clear is the exact way it works (at least in my case at the moment). It doesn't alternate between the primary and secondary every millisecond. (I found some cheap cardboard glasses used for looking at solar eclipses, I know its not the best -.-, going to go buy some welding glass to observe the process). It stays on the primary and a short spark ignites across the secondary sporadically, sometimes it just switches and the process is the same. In my particular case it seems to work quite well as can be seen from the two videos, but I think a lot more can be done to make it truly alternating fire.

I was thinking. What about some sort of SCR or IGBT circuit connecting the primary and secondary which will truly alternate the spark at a given speed determined by the circuit setup? This will truly allow for alternating fire at whichever speed the end user decides?

Thanks
brtaman

Proud Mary

Tue Jun 30 2009, 09:27AM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

In a sense, a rotary gap meets some of your needs, and, who knows, you might even be able to do something with an old electromechanical petrol engine distributor, turn it round with a little electric motor perhaps. An 8-cylinder type might do very nicely at low power with some compressed air blown into it. Who can say?

brtaman

Tue Jun 30 2009, 09:30AM

Registered Member #2161 Joined: Fri Jun 05 2009, 03:36PM
Location:
Posts: 247

Great idea Harry, for the time being, while I figure out if a circuit is doable, I will modify my RSG to alternate. Excellent! Thanks for the tip!

Proud Mary

Tue Jun 30 2009, 09:49AM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Thinking about pages like the historical piece below can sometimes give insight and inspiration, son, and can be a good way of counteracting the conservative tendency to copy existing designs to spare the effort of imagining something afresh.

brtaman

Tue Jun 30 2009, 06:07PM

Registered Member #2161 Joined: Fri Jun 05 2009, 03:36PM
Location:
Posts: 247

Very cool website harry :D

Those are some cool pieces of hardware. Bomac JAN-CBNQ-724B is most eye catching, very interesting piece.

Will post pics of the rotary AFSG later on. I am tired and need to take a rest.

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