are condensors all the same?

[Ned]

Cheers Fred. Though you still need debounce into the base of the transistor

Read what Ned said and come back to me, it is wrong.

I will conceed that you have me on point three, I got sloppy with my terminology, but the rest of what I said is correct, and actually we are talking about the same thing, it is the back EMF that is created by the secondary coil inducing the primary coil that causes the arc.

Its the nature of the inductor in the coil itself to generate back EMF when opening the points on the primary winding. Much like a relay will create the exact same back EMF, which is why they have a flyback diode in parallel with it.

The spark on the spark plus is just because the 20000v+ is enough to cross the air gap on the spark plug.

The arc on the points is generated by the back EMF of the primary winding. Even without the secondary winding there, it would still arc... the secondary winding doesnt cause any arcing on the points.

The reason it arcs on the points is because an inductors job (the primary winding in the coil is just an inductor) is to keep an even current flow, and when you open the points, the inductor magically creates a higher voltage to keep the flow the same. This higher voltage is enough to cross the tiny air gap between the points.

So if you add a capacitor, the flow will go into the capacitor because its the easiest path, (and we all know electricity follows the easiest path) and stops the points arcing

[Rookie]

Your first post is still wrong Ned, because you don't mention any of that, which is the actual reason we have condensers, none of that jibber jabber about creating a clean break of the points ( which just happens to be a nice aside from the reason we use them). I will conceed that my idea of how the back EMF gets created was wrong but it does get created and that is what we are trying to stop, but the fact of the matter is that the condenser is not there to stop 12v burning the points.

[Ned]

Your first post is still wrong Ned, because you don't mention any of that, which is the actual reason we have condensers, none of that jibber jabber about creating a clean break of the points ( which just happens to be a nice aside from the reason we use them). I will conceed that my idea of how the back EMF gets created was wrong but it does get created and that is what we are trying to stop, but the fact of the matter is that the condenser is not there to stop 12v burning the points.

i assumed people knew how a coil worked, and how back EMF worked etc, but obviously not so could have elaborated more about that i guess, but it was late at night and i was in bed trying to get to sleep i can write up a single post with some more detail and clearer points if anyone wants me to? let me know.

It's not the 12v burning the points, its the back EMF voltage on the 12v side that creates the arc/burning. You'll probaby get 50-100v across the point when it opens, even though it's only a 12v circuit... this is the magic of the inductor.

Then the coil will have more windings on the secondary side, so the 50-100v on the primary side, ends up being 20000-40000v on the secondary.

we arent trying to stop the back EMF at all, we want/need that back EMF or else the secondary wont create a high voltage for a spark. If we didnt want that, we would have put a flyback diode in the coil toi stop the 50-100v back EMF

*note; the 50-100v back EMF is a number i pulled out of my ass. I dont actually know what it is and isnt important. I know it's above 30-40 though, as thats what is needed to drive most tachos that connect to the negative of the coil

[fishtailfred]

More epic posts by Ned!

 

50-100 is too low, Ned. It's closer to 400V that you get across the primary on a modern coil. Try driving one with a 100V unclamped MOSFET some time if you want LOLs and magic smoke emission display I actually know of a clown that did this, blew the little IC off of the board LOL.

 

BTW, the secondary voltage only hits what it has to hit If you allowed it to be open it would go sky high. Attached to a plug it goes exactly as high as is required to jump the gap, and (resistance of leads aside) stops there and starts pumping juice through the arc. If you have a coil that doesn't have the boogy to jump the gap of a dirty plug or a high boost cylinder etc, then what you get is peak voltage that lasts until cylinder conditions become more favourable. That is to say that you don't get spark when the points open, rather once the voltage has exceeded the required voltage threshold.

 

Same goes for the points, too, so what you're really doing is buying time to get them far away from each other that a spark can not jump with a lousy ~400V. If you did as you say and clamped it with a diode, you'd get little or no spark, and your engine wouldn't run or would run like a haunted shithouse.

 

Fred.