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ignition coil

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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ignition coil

Unread postAuthor: bighead33 » Mon May 31, 2010 12:22 am

can some body help me find a cheep ignition coil, around 20-30 bucks.
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Unread postAuthor: Technician1002 » Mon May 31, 2010 12:26 am

Junkyard.. Almost free. Find where they shred the cars in your area. Scrap metal places may even give you one. Prepare to harvest it yourself. It costs more if they harvest it.
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Unread postAuthor: jrrdw » Mon May 31, 2010 5:38 am

Depends on what volt you want, 6 volt will probly cost a little more but battery will be lighter. You can get a firing circuit from either one of our sponsors for around 30 bucks and only need a 9 volt or two to work it.
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Unread postAuthor: mark.f » Mon May 31, 2010 6:50 pm

The battery/battery pack used for operating an ignition coil needs to have a fairly low internal resistance. Gel-cells (sealed lead-acid) batteries are preferred, but 8 AA's or a mess of "lesser" cells (9V, etc. in terms of IR) wired in both series and parallel will work also.

Junkyard is about the best you can hope for. If you're not worried for space, the "beer can" type coil will work well, and are held on by a conductive strap. They can also be had from an auto-parts store for around ~$13 if you can persuade a clerk to take you and a price gun to the back to check for the cheapest coil. I can't find the model number on the one I bought, though, so you'll have to do that leg-work yourself.
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Unread postAuthor: bighead33 » Fri Jun 04, 2010 10:17 pm

number one: thanks for all the help you gave me :wink: .
number two: i was look at the pitchers that RC man has for his sparker reference guide and there nothing like the wiki described or the simple battery capacitor.

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Unread postAuthor: jrrdw » Sat Jun 05, 2010 6:01 am

RC man built a custom circuit, the Wiki describes a simple basic circuit.
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Unread postAuthor: rcman50166 » Sat Jun 05, 2010 9:11 am

http://wiki.4hv.org/images/0/05/Ignitioncoildimmer.jpg

This is as simple as is gets. This is also off a 120v AC outlet. Just a dimmer switch and capacitor is all that is required.

Also to aid in your search for cheap coils.

http://www.amazon.com/ACDelco-C500-Ignition-Coil/dp/B000C9N452
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Unread postAuthor: mark.f » Sat Jun 05, 2010 1:04 pm

Also, if you want battery operated and simple (and also low in output voltage), then simply use a switch with a capacitor and resistor in parallel with ground to prevent the back EMF from welding the switch closed (capacitor absorbs the back EMF, the resistor prevents the capacitor from welding the switch as well). You can use a normally closed pushbutton to drive the ignition coil when you push it (as opposed to when you let off a normally open pushbutton), but you should also add an arming switch to prevent current draw when not in use.
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Unread postAuthor: bighead33 » Sat Jun 05, 2010 8:55 pm

O.K. thanks but one more thing, even with out rcman's circuit upgrade my spark will still jump 2in's right?
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Unread postAuthor: mark.f » Sat Jun 05, 2010 9:36 pm

Nooo. Running off of 12 volts with the circuit in my previous post will only provide a spark of about 3/8", maybe larger with a larger coil. If you can find the proper capacitor (termed a condenser in automotive jargon) for the coil you're using you could perhaps create slightly larger sparks, but not by much, and it would need to be wired differently.

If you want 2" sparks out of an ignition coil, I would use a capacitive-discharge-type circuit, a la camera flash-board. The simplest of these circuits would be to wire the coil primary in series with the flash tube (which will act as a switch for the coil when ionized with the trigger transformer). You can also use an SCR in place of the flash tube, though you'll have to order a suitable one from someplace like Mouser or Digikey. See nz_cannons tutorial here. I also made a circuit which could be much simplified (it was designed to run everything on my cannon), shown here.

EDIT: err0r
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Unread postAuthor: ramses » Sun Jun 06, 2010 11:50 am

If you do use a camera flash, I suggest you replace the main capacitor with one around 1-3 uF.

If one was so inclined, you could replace the transistor with a larger one to increase the current capacity (be careful of the transformer) One could use a SIDAC to dump the cap through the ignition coil when the capacitor is charged to whatever voltage.
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Unread postAuthor: Technician1002 » Sun Jun 06, 2010 12:06 pm

In modifying a camera flash to use a "Larger One" is not recommended. The current draw is limited by the frequency and inductance of the coil. Changing the transistor without also changing the transformer is a waste of money and time. A larger transistor may require more gate current, have slower switching due to increased internal capacitance, and in general degrade performance.

Use the inverter transistor that matches the drive current provided by the inverter and matches the inductive load of the step up transformer. Changing only one inverter component is not advised.

Just changing the flash cap to match the ignition coil is good. The inverter will run for a much shorter time to charge the smaller cap.
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Unread postAuthor: ramses » Sun Jun 06, 2010 8:32 pm

Sorry for the bad advice, but the transistor is usually the first thing to blow.

I will add that it really sucks to charge the camera flash just to trigger it and have it not ignite. Then you have to wait ~30 seconds for it to charge again.

The batteries become hot, and run dry after a short while.
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Unread postAuthor: mark.f » Sun Jun 06, 2010 9:31 pm

That's why you replace the capacitor with a ~2 uF one. :wink: Still gives great sparks.
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Unread postAuthor: Hotwired » Mon Jun 07, 2010 8:48 am

0.22uf is even better if you use decent switching to the coil - so not the flash tube.

This one's running on two AAAs with a small coil, recharge time is negligible and runs for quite a while actually. Think I've let it run for 20 mins non-stop before. Frequency drops with voltage though.

[youtube]http://www.youtube.com/watch?v=mOpsWctz9wk[/youtube]

Currently dead because I ran it for too long with a stretched gap/unable to spark ._.
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