Topic: Ignition Theory: Plug Polarity

[Pinhead]

I got it to work. Here's a demonstration.

http://www.facebook.com/v/111293731973

[Alan F.]

Impressive, how did the contacts in the test fixture fair?  What were they constructed of?

-A

[Pinhead]

In the video there is no resistance in-line with the HVDC; the contacts got pretty hot and the rubber fixture got soft and mushy. After all, it might as well have been an instantaneous dead short of 300vdc. :p

My "contacts" are two wood screws shoved through a piece of rubber-urethane.

[MJL]

I got it to work. Here's a demonstration.

http://www.facebook.com/v/111293731973

That is awesome. I was wondering how quickly the plasma ball/arc could be established.

[Pinhead]

I got it to work. Here's a demonstration.

http://www.facebook.com/v/111293731973

That is awesome. I was wondering how quickly the plasma ball/arc could be established.

Too quickly to see. It's just a bright flash of light. It doesn't seem to be any different than the normal spark other than intensity.

[Pinhead]

Here is an updated diagram of how to hook up the HVDC to a single plug coil. Notice that the ignition system itself is left unaltered other than adding two connections.

[Pinhead]

I made somewhat of a strange discovery today (strange to me, at least). After my test fixture melted and my contacts slowly moved further and further away from each other, I found that the HVDC would some times "miss" some of the sparks. That is, the coil would produce a spark across the gap but it would be of "normal" intensity. While playing around with it the rubber finally got hot enough to catch on fire. I moved to blow it out and found that whenever there is air moving through the center of fixture, the spark is massively intensified.

At first I assumed that the moisture in my breath was causing the effect. However, the spark intensity increases even with a fan blowing air through the contacts. I started widening the spark gap more and more until finally the HVDC wouldn't contribute to the spark at all. At about 3/4 of an inch the HVDC contributed no energy to the spark. I verified this by turning off the power to the HVDC and the intensity of the spark stayed the same. However, with the HVDC turned on and air moving through the spark gap, the HVDC fired every time.

Does anybody have any theories as to why this happens?

[Pinhead]

Another update.

Resistive plugs cannot be used with this system. If resistive wires/caps are used, the HVDC has to be applied directly to the plug.

[Pinhead]

Since running the HVDC full-tilt with no current limiting resistors will melt the spark plug, I figured I'd add a little resistance to the circuit. I first tried 600 ohms, assuming 2 amp at the plug would be more than plenty. I put the resistance between the inductor and the voltage doubler. That was a bad idea; the collapsing magnetic field inside the inductive coil set up an increasingly strong high voltage spike that transformed a single spark event into a 5 second arc.  Then the resistors fried, the circuit opened and the show stopped. It was pretty neat while it was going on, though.

In order to block the back EMF from reaching the resistors and the voltage doubler, I simply added a 1000 PIV diode between the inductive coil and the resistors. This has allowed me to fine tune the intensity of the spark by varying the resistance. I think I've settled on ~300 ohms, as visually this resistance has tripled the spark intensity versus a non-enhanced spark. It's not so strong that the spark tip gets red-hot but it's definitely a stronger arc. I'll draw up a new diagram with the parts included.