Ignition coil polarity explained...

[55 Rescue Dog]

I have always hooked up the ignition coil on standard ignitions the way you are supposed to. Power+, and negative to the distributor. Someone brought it up, and I started to wonder why? I stumbled across this article, and it makes perfect sense now. Never really thought about it much before, but it's good to know.

http://mgaguru.com/mgtech/ignition/ig104.htm

[chevynut]

So since the body of the spark plug is grounded, that makes the side electrode negative. Electrons travel from negative to positive. To me that says the electrons travel from the side electrode to the center electrode. The secondary of the coil is referenced to the + terminal. So how does this work?

[55 Rescue Dog]

Only someone like Nikola Tesla could know. I will never know enough about electricity. It is FN magic!
There are 2 schools of thought on electron flow. Magnetism is even a bigger part of electricity, and with Tesla's AC, the electrons are switching directions, at any frequency, at any voltage, at light speeds, and makes the magic happen. We are surrounded by AC waves, and it travels around the earth 7.5 times in one second, and beyond. It makes me feel stupid. Just check out the
electromagnetic spectrum. They never mentioned that, or Tesla in school. Why?

[BamaNomad]

Electrons move from negative to positive, but holes move from positive to negative...

[55 Tony]

As for the direction of the current, when the "points" open, the collapsing magnetic field in the transformer (coil) gives the pulse in the opposite polarity compared to the polarity of the circuit of when the magnetic field is being charged with the battery.

Voltage on the primary side of the coil when the magnetic field collapses is also much higher than the 12 volts supplied to it. If it doesn't scare you, try touching the two terminals with just a single D cell and feel the shock it gives you on the primary side when you disconnect the battery. That higher voltage is then multiplied even more in the HV winding of the coil. The purpose of the condenser (capacitor) is often debated, but I'm with the group that says it's there to help *absorb* that voltage spike from arcing across the points and causing premature failure.

I'm going to have to try that pencil test, it looks pretty cool!

[55 Tony]

test

[carls 56 (RIP 11/24/2021)]

had a 49 dodge that was positive ground. never did get that,HPIM0944.JPG but loved that car. HPIM0940.JPG

[55 Rescue Dog]

There are some good animations on how ignitions systems operate.

https://www.youtube.com/watch?v=UEmSFDn8Rlw

[55 Rescue Dog]

Another one.

https://www.youtube.com/watch?v=W94iksaQwUo

[55 Tony]

They are good, thanks.

[55 Tony]

why is there a required (with specified gauge) gap between the points in the contact breaker if it only needs to close the points in order to let current pass through? is there no need for current to make an arching?

The gap size, or "dwell" (time) is because it takes a certain amount of time to saturate the coil windings when the points are closed. This time is far from perfect with points because the time changes with the speed of the engine. It is a happy medium to make it run well at different rpms.