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need info on ignition system

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: saefroch » Thu Sep 22, 2011 7:50 pm

Pictures help, as well as details about your fueling/venting... as requested above.
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Unread postAuthor: Hotwired » Thu Sep 22, 2011 8:12 pm

dave6187 wrote:
ramses wrote:
Or you could dump your fly swatter into an ignition coil.


I just tried doing that, and it straight up didn't work, I know my coil is good, makes a OK spark off of a 9v, hooked the circuit up to it, transformer just whined, changed a few things around, nothing. put it back to the way it was, nothing.

I'm at a loss, and am pretty much about to run 18 volts (2 9v) to the coil, and put a switch in line as a breaker and make that my ignition source. unless someone has a better idea.


For a fly swatter to work with an ignition coil you need to hold a larger charge than the swatter normally holds and then pulse it to the coil.

To increase the charge you need a capacitor of suitable voltage across the fly swatters output of about 0.22uf.

To pulse it to the coil you can indeed just touch wires to make and break the circuit.

Or you can use a gas discharge tube, SIDAC or anything else which conducts current extremely well when it reaches X voltage.

Each time the capacitor charges to X voltage the energy it stores is pulsed across the ignition coil. The capacitor is drained and starts charging again.
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Unread postAuthor: dave6187 » Fri Sep 23, 2011 2:02 am

ok, this is what I ended up doing... using the ignition coil and disposable camera instructions in the wiki as a guide, I was able to build a circuit that charges the coil, which would probably bridge over a 2in gap, right now I have it gapped to a touch over an inch. I set it up with a "remote" ignition, which was basically an old window switch, with 2 9v's attached, to trigger the relay, has about 2ft of cable on it. use a AA to charge the camera, i just need to get a AA holder and a kill switch. I am more than thrilled with how it came out, I wanted to do a dual spark, and still can, but this should be plenty.


dunno how to post a video, but this is the spark i'm getting now:


http://www.youtube.com/watch?v=zT9hfgWcbPE

and an fyi, i've been using static guard for fuel, haven't done much with venting but going to look into it
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Unread postAuthor: jackssmirkingrevenge » Fri Sep 23, 2011 2:12 am

dave6187 wrote:haven't done much with venting but going to look into it


You definitely need to remove the combustion gasses after each shot in order to allow sufficient oxygen to feed the next shot.

Even with the best ignition in the world, having an incorrect fuel mixture will not give you a reliable setup. I strongly recommend syringe metering of propane or butane.
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Unread postAuthor: dave6187 » Fri Sep 23, 2011 2:16 am

I will definitely look into that method of metering fuel, never even occured to me to do somethign like that. this is why I like these boards :D

and I definitely understand that gasses need to get vented out, i usuallhy do 2 or 3 shots, and leave the end cap off for a while, and go at it again
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Unread postAuthor: jackssmirkingrevenge » Fri Sep 23, 2011 2:38 am

dave6187 wrote:and I definitely understand that gasses need to get vented out, i usuallhy do 2 or 3 shots, and leave the end cap off for a while, and go at it again


It's better if you actively remove the gasses by injecting compressed air or blowing into the chamber, or even swinging the launcher around with the end cap off.
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Unread postAuthor: enauman » Sun Oct 02, 2011 11:23 am

What kind of power is available on your cannon? Is it hand held or mounted? I designed a multi-spark high voltage ignition system that uses a pulse generator, IGBT and an automotive coil. Generates 3 rapid 50KV sparks on an automotive spark plug. Never fails. But you have to be able to assemble some electronics and have the room on your device for a coil, battery and a small electronic enclosure. If you think this might work for you, I can send you a schematic.
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Unread postAuthor: Mr.Tallahassee » Sun Oct 02, 2011 3:00 pm

I built a system from an electric fly swatter that puts out close to 200Kv. Here's the video. [youtube]http://www.youtube.com/watch?v=hrw4X5L2tkk[/youtube] All you need is a HV switch which is easy to make.
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Unread postAuthor: dave6187 » Mon Oct 03, 2011 6:07 am

enauman wrote:What kind of power is available on your cannon? Is it hand held or mounted? I designed a multi-spark high voltage ignition system that uses a pulse generator, IGBT and an automotive coil. Generates 3 rapid 50KV sparks on an automotive spark plug. Never fails. But you have to be able to assemble some electronics and have the room on your device for a coil, battery and a small electronic enclosure. If you think this might work for you, I can send you a schematic.


if you could send me a schematic that would be awesome. what kind of battery we talkin about? the system I currently designed has a camera flash circuit, hardwired to keep charging whenever power is applied, driven by a AA. it discharges through a relay, into an ignition coil. the relay is controlled by 2 9v (tried using one, but it didn't work after like the 3rd time) wired through a remote switch. when it works, it works well, but the recharge time gets annoying, and when it was humid the other day, just about everything except my spark gap, sparked. a 30kv spark to the leg hurts a bit.
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Unread postAuthor: Technician1002 » Mon Oct 03, 2011 2:53 pm

dave6187 wrote: I currently designed has a camera flash circuit, hardwired to keep charging whenever power is applied, driven by a AA. it discharges through a relay, when it works, it works well, but the recharge time gets annoying.


Replace the flash capacitor with a metal film cap in the value of 0.22 to 2.0mfd for fast cycle times. The big photoflash cap is overkill for the ignition coil.
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