Electronics electonic ignition

we made a potato gun, which uses hairspray as a fuel and two screws to ignite it...

anyway, we use a grill sparker thing to ignite right now, but that doesn't seem to have enough voltage to be really effective....

so I decided to start making one that uses batteries and some other stuff (button, wire, capacitors, ect) to create a really good spark. the only problem is that I have no idea what kind of ciruit to use...

this is what I want it to do;

1. charge a capacitor
2. light up an LED when charged
3. use the button to discharge into the screws
4. and recharge when done

I already have

• button
• 2 diodes (12v 21 mA)
• battery case (2 AA)
• LED (white 3.6v 20mA)
• capacitor (47 uf)

if anything above won't work, let me know and I'll get something that will

 

You could charge up a capacitor (several hundred microfarads) to 18 volts (two 9 volts in series) and then discharge it through the secondary of a step-down transformer.

 

Try using a CC inverter with the input connected to a 9v battery through a switch.

 

Or maybe an ignition coil from a car? A 9V battery on the primary side should give you enough juice out of the secondary.

 

thatnks for all the suggestions, now ann I need to know is how to put any of this together

 

I built a similar circuit to fire my coilgun, except it worked on about 98 volts at a peak current of ~1000 amps for a very short time (current was important, not voltage). Basically though, you need a 555 timer circuit driving a transformer in reverse to charge a large HV cap, then you close a switch or use a relay or something to discharge the cap accross a spark gap, basically the same as a condenser in a car's ignition system. The idea is that you convert a small amount of POWER over a large amount of time into a large amount of power over a small amount of time. The net ENERGY in joules (1 joule = 1 watt for 1 second) was extremely small, actually slightly less than that delivered by the batteries (which were four AA's). The circuit wasn't very efficient, but i'm sure it could be made to be extremely efficient by someone who actually knows what they're doing

 

Even simpler, get a large inductor and charge it up from a battery. Quickly stick your leads onto or into someone and remove the battery. The back emf spike will be enough to suprise or incapacitate depending on the voltage and the size of the inductor (I'm only suggesting you do this and will not accept any responsibility for anything that happens should you attempt to do it).

 

That method is kind of useless for firing a potato gun though, because not enough net energy is created for a spark, unless you use a really large inductor.

 

Oh yeah, I forgot you were trying to create a spark. Most of the requests for high voltage have to do with shocking people and I forgot this wasn't one of them despite having read it. How much arc do you want? 1/8 inch? That's about 2500 volts. You should be able to get that with 12 volts and an iron core multilayer inductor that's smaller than a soda can.

 

for mine, i bought a couple battery powered bbq ignitors, they run off a single AAA battery, and provie a nice blue spark over my big gap....i found 'em at a liquidation store for like $8, and got one free, cuz with the purchase, i got a coupon for like $10 free...