Ignition/Fan Circuit
This is a circuit I designed to control both ignition and the fan on a combustion cannon I had in the works... until recently. I designed it to run on any voltage between 12-35 volts, and fit inside of a handle constructed of 2" SCH-40 pipe.
I made an early prototype which was supposed to create a repeating spark from the ignition coil. While it worked, it did so unreliably, because the switching method from the capacitor to ignition coil was a very tiny, very fiddly spark gap. So, I decided to use an SCR instead to switch to the ignition coil.
The ignition section is composed of the boost side of a camera flash circuit which charges a 400V film capacitor, which is discharged through a silicon-controlled rectifier through an external ignition coil. Simple.
The fan control side is simply a 12v voltage regulator and a running indication LED... too simple.
The circuit is constructed on perfboard with leads for the switches, LED's, loads, ignition coil, etc. It measures about 1.5x2.25".
Below are some tentative beginning schematics and the completed circuit... and results.
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