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Help with ignition coil

Post questions and info about hybrid (compressed gas with fuel) powered cannons here. This includes discussion about fuels, ratios, ignition systems, build types, safety, and anything else relevant.
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Unread postAuthor: jrrdw » Tue Oct 19, 2010 7:40 pm

Technician1002 wrote:The coil damage when running on a 9 volt battery is most likely caused by not grounding the coil shell causing insulation failure between the iron core and primary.


You lost me here, the coil is/has a plastic case. It's a insulated casing. They've been made that way since Fnord's birth and before...
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Unread postAuthor: Technician1002 » Tue Oct 19, 2010 7:58 pm

The tower top is plastic. The can the coil is in is iron. Scrape the paint and take a look. The mounting bracket is used to connect the can to the grounded firewall or engine block. This connection is required for proper operation.

Most tower style ignition coils as shown have the other side of the high voltage lead internally tied to the + terminal of the ignition coil as shown in this diagram;
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Unread postAuthor: whoa044 » Wed Oct 20, 2010 6:41 pm

Are you sure you need to connect the ignition coil casing to the battery negative?

This website doesn't include it anywere. Clicky

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Unread postAuthor: Technician1002 » Wed Oct 20, 2010 7:23 pm

They also show the high voltage coil tied to the - terminal internally which is rarely done. Most of the time it is tied to the + terminal.
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Unread postAuthor: ramses » Wed Oct 20, 2010 7:55 pm

I have to ask: Does it matter that much? I mean, there is a (relatively) small amount of wire between + and -, this voltage would theoretically be added or subtracted from the secondary tap voltage.

If you want to know for sure, use an ohm-meter.
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Unread postAuthor: whoa044 » Thu Oct 21, 2010 2:38 pm

Through previous experiences when I've used camera flash circuits for charging/discharging capacitors to the coil, I realized it can be cheaper, and easier to buy a 30kV ignitor from spudfiles. But that isn't as fun making :P

edit:
Imedence from positive in, to high voltage out is: 8.81 kOhms
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Unread postAuthor: ramses » Thu Oct 21, 2010 4:33 pm

now from negative to HV out? the lower resistance one is the one to arc to. You may not be able to measure it; The primary resistance on mine is something around 10 ohms. That's why I said it probably doesn't matter.

A 30kV ignitor is cheaper, but I already have the ignition coil setup. I just need to fix it for the contest so I can hopefully have a shot at 2 for free.
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