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Another nembie Q:

Post questions and info about combustion (flammable vapor) powered cannons here. This includes discussion about fuels, ratios, ignition systems, safety, and anything else relevant.
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Unread postAuthor: rp181 » Wed Aug 06, 2008 2:32 pm

when DYI said overly powered ignition system, i think he was talking about high energy arcs from capacitors.
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Unread postAuthor: DYI » Wed Aug 06, 2008 8:36 pm

How do you class powerful? My ign system draws on a 12v 300amp battery.


If it can't detonate TNT directly, it ain't high powered :wink:
I believe you're using an induction coil to create the HV, so you don't need to be worried about getting any decent energy out of it.

And FAEs do detonate. Not very quickly of course (I believe well under 4km/s on average), but if you see a really slow motion video of one going off, you'll understand. They set off the fuel/air mix with an explosive charge in most cases, that goes off a preset amount of time after the burst charge.
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Unread postAuthor: jimmy101 » Thu Aug 07, 2008 1:30 pm

Ballistica7 wrote:How do you class powerful? My ign system draws on a 12v 300amp battery.

You really can't gauge the power of the ignition from the power of the voltage source. How much current does it actually draw? It almost certainly doesn't draw the full 300A the battery is capable of.

And, if it is any type of capacitive discharge system then the current rating of the power supply is pretty much irrelevant. A 1.5V AA battery (sources ~10A, 15 watts) charges a photoflash cap to about 6.5J in several seconds. The phtotocap will dump that charge in ~1mS. That's 6,500 Watts (1J = 1W*S). Basically, the photocap discharge system compresses a couple seconds worth of power from the battery into a ~1mS long pulse. That 6,500 watts is about twice what a 12V, 300A battery can do continously.

Propane + air at 1 ATM requires a few hundred microjoules for ignition.
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Unread postAuthor: McFear » Thu Aug 07, 2008 8:54 pm

you just answered a question i was about to ask., thanks very much:P
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Unread postAuthor: SpudFarm » Thu Aug 07, 2008 9:01 pm

i just started to think about ignition.. a wire from the tungsten electrode on a tig welder to the spark gap and then the other (don't know name in english) on the chamber..
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Unread postAuthor: McFear » Thu Aug 07, 2008 11:08 pm

cathode? thaty what your looking for
positive terminal or have i got it wrong way around
[url][/url]
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Unread postAuthor: jimmy101 » Sat Aug 09, 2008 11:51 am

SpudFarm wrote:i just started to think about ignition.. a wire from the tungsten electrode on a tig welder to the spark gap and then the other (don't know name in english) on the chamber..

I'm not familar with TIG welders, but don't regular arc welders require contact between the electrode and the work to "ignite" the spark? A standard arc welder wouldn't work as a spark source for a spudgun.
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