Fun with spark plugs

Yes, that is pretty crazy.   I figured by the time I returned the wire would have been a dead short.    If I put a boot on it I could take the pressure up higher or I could put it on a DC power supply and see where it falls apart. 

Edited by geek - Yesterday at 11:34am

So you want to see some faster speeds....

For this next test I made up a little capacitive probe to clamp onto the wire.   Jist is similar to the cap wire.  The clamp goes to another cap to setup a divider network and this is fed to the scope.   I tried to test the probes flatness with little luck.    There is no DC or low frequency response and it is not flat anywhere.  Just an overall bad setup.   You can buy a probe like this for $50 or so and maybe get some better results.   



This first plot shows the standard wire with no braid.   We can see the Arc time is about 20nS.  



Next we can see the effects of the braid on the wire.     You can see that it is not real stable.



This old scope can run in RIS mode and has an analog BW of 4GHz.   For the time, it was bleeding edge.   

When running this mode you have to limit the inputs (normal for a high speed DSO) and the trigger would have to be very stable.  In this case it's not so the phase noise is bad. 

Anyway, here is the rise time of the standard wire.




Now, my guess is this is not really what it looks like.  I mean, getting back to my home made clamp on probe.  We would be kidding ourselves. 


It does appear that my home made capacitor wire has little effect.

Originally posted by geek Next we can see the effects of the braid on the wire.     You can see that it is not real stable. It does appear that my home made capacitor wire has little effect.

Shape of the line is like discharged capacitor. Maximum current was the same in both cases(?) Can you tell what is maximum value of current? This was in open air? Capacitor effect should increase when breakdown voltage increases because energy stored to capacitor increses (E=C U^2). What was the wire resistance? In nology wires that was 460 ohm. Longer wire and incrased resistance should increase discharge time (and reduce current).

Capasitor will decrease voltage rise time. That will have to have some effect to boot breakdown. Maybe boot breakdown will only happen with CDI-ignitions. I suppose that with magnetos and coil ignitions voltage rise time is longer.