Making a compact igniter for an engine

I have struggled with the use of sparkplugs in my engines, simply due to their need of a large box of electronics hardware and wiring simply to get a few sparks for ignition. Using a blowtorch to start an engine is much harder than traditionally using a sparkplug, but sometimes the initial set up time of the sparkplug can more than offset this.

I want a small, reliable spark generator, filled to the brim with electronics in as compact a form as possible. It should be capable of consistently releasing 20,000V sparks, be efficient on the battery, be robust, and only be activated through holding a button down. This is because in my previous designs of this, I used a system with safety switches and arming switches, which added size and weight. This new design will be made in a way that requires me to hold the HVG directly against the sparkplug itself, eliminating the risk of accidental firings.

For the enclousre, I found an old laptop power supply, which was beaten up but still in great shape structurally.

 

 

After using a chisel to pry both sides apart and removing the electronics inside it, I was left with a shell that I sanded down until all the paint and inscriptions were gone. I then measured out and drilled a hole for the momentary switch: 

 

For the paint job, I wanted to try something new. I opted to paint it a glossy white as a base coat, then place an onion wrapper bag over it and paint the top black. I then sprayed droplets of white over this again for a unique finish.

I wanted to use the same high-voltage generator (HVG) as last time, as well as a 9V battery and a momentary switch, instead of 2 toggle switches. The red and green wires take in a maximum of 6 volts, and output the high voltage across the gold wires. I am using a 9V battery as the duration of the pulse will be very short, just enough to start an engine. It doesn't have any fancy chips or 555 timers in it, just a transistor, a transformer, and some resistors. The small 6V DC supply first goes into one winding of a transformer. Then the 6V voltage is dropped with a large resistor, and goes into the base of a transistor, which turns it on.

The transformer builds up a large amount of magnetic energy in the core until it is saturated, and can't hold any more. When this happens, the magnetic field collapses, dumping a high voltage over the secondary lines of the transformer. This also induces a voltage in the opposite polarity of the 6V, causing the transistor to shut off quickly. After a large pulse of voltage is sent, the transformer no longer opposes the 6V supply, which can then turn on the transistor again, allowing the transformer to build up magnetic energy again and repeat the cycle. This is why these cheap DC high-voltage generators produce pulsed arcs. 

This momentary switch was completely made of steel. It included an O-ring to form a perfect seal when screwed tightly against a surface. The issue with this design was that it could not be placed anywhere near the output of the generator, as it would have the tendency to shock whoever was unfortunate enough to press the button. This turned out to be a very tricky design consideration due to how compact I wanted the contraption to be

For the output, I used two bolts. This is so that I could push the wire between the bolt and the plastic wall, then tighten a nut on the other side to sandwich the wire in place securely. The high voltage would arc between these bolts, as the HVG tends to burn itself out if it doesn't have a place to dump the voltage across, eg if there is no place for the output to arc, such as when the leads are held too far apart. This design ensures that even when the sparkplug is not connected, pressing the button will still cause an arc to be made and keep the HVG safe.

I knew that housing a 9V battery, a switch, and a HVG with wires would be a tight fit, but it was only thanks to CAD that I managed to get everything to stay within the constraints of the box without bending it. The fact that it was so tight meant I didn't even need to glue any components down as they fit snugly with no play. 

To keep the top half secure, however, I needed a system of squeezing the top half and bottom half together evenly. I decided to use 2 bolts for this, but the only bolts long enough were 5cm long, almost twice the height of the box itself. I cut these down to size with an angle grinder and drilled 2 holes in the top and bottom plate, making detailed measurements to ensure they lined up and did not interfere with the placement of the HVG and battery. Finally, I was left with this:

 

Which produced stable, consistent, strong blue arcs with the simple press of a button.