Automotive Ignition Coil Humming

[Project23D]

About a year ago I learned how to NOT make a automotive ignition coil hum/whine.

I was playing around with the ignition system on my car, learning from a source that a larger, hotter, spark will cause a more complete combustion inside an internal combustion engine (ICE).

So, using a pulse circuit I built connected to an IRF520 (or something, used to increase current handling ability), a cap probably 50,000uF, an ignition coil from the junkyard and a computer switchmode power supply, I built my test setup.

The pulse circuit had a pot that was used to adjust the frequency, and a LED to have some kind of visual of what was happening. Also a freq counter connected up so I could see what freq the circuit was operating. Because just about everything about the pulse circuit was crappy, the damn thing was unstable and bounced everywhere.

My spark gap was about an inch or so and watched as I increased the freq, the spark got brighter and louder. I was able to get to about 500KHz before the first pulse timer chip blew up. The ignition coil started to quietly hum around 100Hz and then began to whine around 900Hz or so. In the higher freq range the coil became rather warm, and the main charge capacitor began to whine as well.

After deciding to have a few more tests, I'm not sure what I did as my power supply made a funny noise and so, it was the end of that.

Lesson learned: for pulse testing, next time I'm going to use a battery and/or linear power supply with back EMF protection so I don't ruin a good, reliable power supply.

[powerlabs]

I ran one off a microwave oven transformer; it was charging up a capacitor and an SCR discharged it into the coil at about 1.5KHz. I could hear the oil boiling inside the coil after a couple of seconds. It made a really hot spark but also ate expensive stud type SCRs on a regular basis... The coil is fine at high frequencies, but they don't like running at very high currents. You also have to keep the pulses short, otherwise the coil saturates and all the extra power you put into it just becomes heat in the windings...