Camera flash ignition setup

[Pete Zaria]

Over the past few days, I've tinkered with a few camera flash circuit boards. I built a altoids-can size tazer, and a mini arc welder (more capacitors!). Of course I might as well build one for my combustion gun, since it's currently using a BBQ sparker.

Here's my question. I could use the camera flash alone by using a 3-point spark gap (the two leads plus the camera's ground, which is required to ionize the air in the spark gap to allow for an arc), or I could use a relay and ignition coil. Which method is preferable? Why?

Thanks.

Peace,
Pete Zaria.

[jrrdw]

If your looking for raw power, i think it's the ignition, stock chevy coils put out about 35 to 40 thousand volts dc, has to be this much for the spark to happen in a compresstion situation. I have never fooled with a camra flash before, but i somehow can't imagine them haveing the power of a ignition coil.

[carlbelcher]

35K - 40k volts isn't very much... Even a $11 stun gun can produce 100K volts and some high-end stun guns a produce 900K volts.

I wouldn't use either, ignition coils are heavy are require large 12 volt batteries and camera flash circuits are underpowered and overcomplicated. I would use a stun gun, you can get one for $10.95 that will give you twice the voltage of either of the other two.

[FiveseveN]

It amazes me how the simplest multiple-choice questions can lead to such offtopic discussions.

And to answer Pete's query: If you already have an ignition coil I say dump the cap through it, but use the flash bulb as the switch, since solid relays could become welded shut and will degrade over time. All you'd have to do is put the coil in series with the bulb. You could add capacitors in parallel with the existing one to increase power (also increasing the time it takes to charge).

The trigatron solution is just not reliable enough: conductivity depends on the density of the gas (fuel/air mix) and we all know how hard it can be to get the mix just right.

If you're planning on buying an ignition coil, I say buy a stun gun instead. And if you can't own a stun gun, buy an ignition box from spudshot.com or whoever else sells them.

[carlbelcher]

Here's my question. I could use the camera flash alone by using a 3-point spark gap (the two leads plus the camera's ground, which is required to ionize the air in the spark gap to allow for an arc), or I could use a relay and ignition coil. Which method is preferable? Why?

I'm not sure what you read fiveseven, but it seems to me like he's asking if he should use a ignition coil or a camera flash circuit...

[FiveseveN]

What ever helps you sleep at night, Carl

[Pete Zaria]

Thanks for all the input.

I'll probably just buy a stungun. It's no problem for me to get one.

To be honest, I just wanted to see if I could build a better ignition (better than a piezo BBQ sparker) out of parts I had laying around the house.

I can get a used ignition coil free from a buddy that works at a junkyard.

I already have a camera flash circuit built and put into a project box with a safety switch, firing button, "charge" button, and armed light. I installed a Molex connector (from an old computer PSU) to the front, so you can unplug the box from the cannon.

The thing is, to make a spark gap with a camera flash, you have to use 3 wires instead of just two. The third wire is a ground of sorts, that's required to ionize the air inside the spark gap and allow the voltage to arc across the gap.

To make this 3-point spark gap, I cut out a half-inch long section of 1.5" scrap ABS and drilled 3 screws into it, spaced evenly, to leave a 1/4th" spark gap between the three screws in the middle. Then, hook up the main output from the camera flash to two of the screws, and the ground (which is normally connected to the flash bulb enclosure) to the third screw. This will produce a nice, big, hot spark, around 330V. I plan to mount this little spark gap contraption inside my chamber, in front of the fan.

My question is, is it better to use this 3-point spark gap setup, or just dump the camera flash through an automotive relay and ignition coil, allowing a 2-point spark gap?

I know a stungun is better. I'll probably just order one. Anyone know a site that sells them for $15 *including shipping* ?

Thanks for the info, as always.

Peace,
Pete Zaria.

[carlbelcher]

I don't know how well using a automotive coil with a camera flash circuit will work... an automotive coil will increase the voltage but only at a loss of amperage. By the time you get done converting 1.2volts to +/- 330 volts (which is what the camera flash circuit does) you're not going to have much amperage left to convert to a higher voltage. So not only will the coil drop the amperage to a nonexistent level but also automotive coils are quite inefficient (especially old junkyard ones) so you will probably lose what little power you had to start with.

Side note to FiveseveN: I was simply explaining to you that I answered Pete's question... You're the one who didn't understand what he was asking.... Not me.

[FiveseveN]

Tisk, tisk, tisk, people. Don't make me unleash the grammar dogs
It's all good fun, but I'll try to make things clear:

ONE: Trigatron = triggered spark gap, as in 3-point spark gap. The 3rd electrode is not a ground, it carries quite a bit of charge in order to ionize the gas between the two "main" electrodes.

TWO: The camera flash circuit is not a simple step-up transformer and neither is the ignition coil. The flash circuit charges a capacitor so it holds quite a bit of power, which it dumps suddenly upon the poor halogen-atmosphere triggered spark gap which we call a flash bulb. If you don't believe me, touch the electrodes of a 1.5v battery, then the electrodes of the charged capacitor and THEN tell me it's the same energy Sounds like an episode of Brainiac. So basically you DO have 'nuff amps to dump through a step-up transformer, which brings us to the next point:
The ignition coil is a special high-impedance autotransformer (meaning the primary and secondary share the ground, not that it's used in automobiles) that actually stores energy itself. It's not a capacitor, more like a short "delay" that buffers a burst of energy before discharging it through the secondary's load.
THREE: in the end, it must be said that camera+ignition coil set-ups have been used in the past and do work nicely. Whether it's a better solution than a stun gun, I don't know. It's kind of bulky and heavy, plus it takes a good while to charge up. But if you already have all the parts or you could get them for free, why spend a dozen bucks on a stun gun? I'm poor. I tend to think that way more often than I'd like to admit

[spanerman]

ive spen all afternoon tinkering and with two 330V caps i can get a relible sprk to light alcohol but make sure you add a switch in the line and jumper the terminals on the pcb so you bipas the switch on there(the one that charges the coil. i also recomend that you take the wires derecly fron the caps instead of the bulb so you completly bipass the big voltages through the wires instead of the pcb whic could melt(yes it happend) and voila you have 660volt reasonable ampage ignition sysyem for vertualy no money




sam

[DonTheLegend]

I use an ignition coil on my old setup, worked great. The only thing i had trouble with was the fact that my camera flash circuitry was a little finicky (my fault, wasn't very good at soldering or anything then), but the ignition coil worked. Never tried it a trigatron setup though.

[GalFisk]

To be correct, the flash bulb doesn't contain halogen but Xenon gas. If you don't have an ignition coil, the voltage an be dumped through a flyback or the secondary of a small mains transformer as well.

[spanerman]

ok couple of questions..... im using 4 caps should i wire them in series or parralel?? and should i use the third wire???

[singularity]

i wire mine in parralel just cause i prefer current over voltage, but if you really want to get some power out of it find an old tv and rip the flyback out of it

[GalFisk]

You should wire the caps in parallel, wiring them in series will decrease capacitance.
The third wire should be used if you don't have a step-up transformer, to make a triggered spark gap.