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ignition coils

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 coils

Unread postAuthor: singularity » Fri Jun 08, 2007 10:23 pm

alright i have an ignition coil driver which is producing a 4 to 12 kHz 18volt signal across my ignition coil... but for some reason im not get the mad crazy 1/2 sparks that should go with it. in fact im not getting any sparks at all, i know there is a 4 to 12 kHz signal because i measured it with a $200 volt meter which is incredibly accurate. so i have to ask is there such a thing as a wrong type of ignition coil? this one is bran new, fresh out of a sealed box, any way i can test it?

on second though, can i test it with a flyback transformer? or it the frequency wrong? any one know how to wire a flyback?
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Unread postAuthor: jimmy101 » Sat Jun 09, 2007 9:05 am

How much current will your driver supply? To work properly an ignition coils needs a lot of current.

Usually, the driver circuit would be driving a high power transistor which in turn is directly controlling a pretty powerful power source. A car battery can put out several hundred amps.

What is the waveform of your driver circuit? Square, ramp, sine...? The coil will work best with a nice square wave. It'll work like crap with a sine wav.

Gives more details about your driver circuit and how you have the coil wired.
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Unread postAuthor: singularity » Sun Jun 10, 2007 1:40 am

the driver circuit is a ne555 hooked up to a 2n3055, as far as i know its a square wave, but i don't have an oscilloscope to check that. as for the power source... about how many amps do i need? i had i hooked up to a 480watt pc power supply which probably has 20 amps on the 12v rail. i do have a car battery but im scared every time i hook something up to that thing its gonna explode. i measured the resistance between the positive and negative terminals to be 1.5 ohms so im going to guess like a 8 amp draw on the battery wouldn't be to bad right? the plan for this thing was to be a igniter for a small hydrogen cannon, any ideas for a small battery i can use?
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Unread postAuthor: jimmy101 » Sun Jun 10, 2007 12:12 pm

Singularity:
A 555 puts out a square wave which is what you want.

Do you know what the current rating of the 2n3055 is? I believe it is roughly 10A transistor which should be enough. Though it probably needs a heat sink. Are you sure you haven't fried the transistor? (a very easy thing to do) To test you can disconnect the coil and replace it with a 12V light bulb or an LED (careful of polarity) + ~500 ohm resistor. If the light (or LED) doesn't light up then you probably fried the transistor.

Do you have a flyback diode on the coil? When the current to the coil is turned off it will try to drive whatever is connected to the its + terminal to a negative voltage. That is another way to fry either the transistor or the 555.

The PC power supply might not work well in this situation. Many PC power supplies must have at least a 5 to 10% load or they won't turn on properly.

Try hooking the power supply up directly to the coil. When you disconnect the power supply you should get a spark. You might or might not get a spark when the supply is connected to the coil.

It sounds like you are working from a published design. Please post the url.
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