i guess this might be a newbie question but the electricity comes out of the secondary coil, goes through the spark plug, then how does it get back to the secondary to make the complete circuit? the coil casing is completely covered i cant find a ground spot anywhere. its probly a simple answer but never the less i cant figure it out and it pisses me off.

 

ok i just realized im retarded, i know the wires go from the coils to the dizzy not plugs, but still i cant see the complete circuit

 

is it the engine?
i think that the ground is the engine itself.

 

well yea but i mean i cant find any spot on the coils where it could be grounded

 

the coils are not grounded.

there is the primary, which is + & - and then there is the secondary which goes to the spark plugs.

Current is run throught the primary coil until flux builds up in the coil, The primary coils power is cut and the buildup of flux collapses accross the secondary coils and creates a large voltage. which goes through the plugs and grounds through the engine.

 

i know that but the voltage that is built up in the secondary is between the 2 ends of the coil, there has to be a complete circuit so how can it work when its grounded to the battery which is a 12V circuit?

 

There is no voltage build up in the secondary winding of the coil, until the current to the primary is cut.

The primary terminal of the coil is connected, internally, to both the primary and secondary windings. That is , they both get 12V from the primary positive terminal. When the ignitor grounds the primary negative, you have a given current through the primary coil. Nothing happens in the secondary yet.

When the primary current is cut (again, by the ignitor which is just a current controlled switch, but a switch all the same) it induces a current in the secondary. The secondary has many more turns than the primary, so it produces a much larger voltage than that applied (12V), but has a lower current, so power remains the same. (As it must.)
The high secondary voltage seeks a ground, and the best available, normally, is to arc across the gap of the spark plug.
(Which is why oil covered or cracked lead wires, cracked coil secondary insulators, etc lead to misfires: the spark will take the path of least resistance to ground. But you knew that, I suspect.)

Short answer: the secondary is connected internally to 12V and grounds though the spark plug.

-John.

 

you said the secondary is internally connected to 12V but the secondary coil produces something like 30000v - you cant mix voltages like that. ill try to explain my question/point of view better..........ok the secondary coil is just a long wire coiled up and there are 2 ends of the wire. and as you know you have to have a complete loop for the circuit to work. one end of the secondary coil goes to the spark plug and the spark plug is grounded to the engine/chassis......and you say the other end is connected to the same wire as the primary inside the coil.....how can a 30000 volt circuit be grounded into a 12V circuit???

 

Yes, you can.
Every time you plug a Walkman into the wall socket, you convert 110V AC to about 12V AC, or whatever (then it gets converted to about 6V DC, which is a separate issue.). Same principal, except with an ignition coil you bump the voltage up, and cut the current in the primary abruptly to get the large increase.

...ok the secondary coil is just a long wire coiled up and there are 2 ends of the wire.
Yup. And the primary is the same thing. It's the ratio between the number of turns of the primary and secondary wire coils that determines the voltage increase/decrease.

and as you know you have to have a complete loop for the circuit to work.
Yup.
The primary gets 12V and is grounded through the ignitor.
The secondary gets the same 12V and is grounded through the spark plug.
Two separate circuits, but linked by induction within the coil.

one end of the secondary coil goes to the spark plug...
Yes
and the spark plug is grounded to the engine/chassis......
No, only part of the plug is grounded. The secondary lead goes to the center electrode. The case of the plug is grounded. That's what makes the spark: the 30,000v will jump across the spark plug gap to get to ground.


and you say the other end is connected to the same wire as the primary inside the coil....
Yes: the 12V supply. Same manner as you supply your stereo and fuel pump with the same 12V: they are connected together, but don't "short" or interfere with each other. The two windings within the coil are supplied 12v by the same terminal in the same manner.


how can a 30000 volt circuit be grounded into a 12V circuit???
The 30,000 volt circuit (secondary) is grounded through the spark plug, when it jumps the gap.
The "12V circuit" (primary) is grounded by the ignitor.

The two windings do not touch each other, they are separate circuits to an extent. Both fed by the same 12V from the same terminal. As they are coils, in close proximity, the switching of the primary affects the secondary (inducing the 30,000 V.

A diagram from the net:


If it still doesn't make sense, you might do a search on Google for induction to understand it better.

-John.
[/B][/QUOTE]

 

Nothing is shared, if you look at it that way. If I touch a 9v battery to my tongue as they hit me with the defibrilator to restart my heart, I'm closing the circuit on a 9v battery and a ??? Kvolt piece of medical equipment.

That being said, in this case I think the coil is grounded, and the engine block itself is tied in to the same ground.

 

FJ's post wasn't there when I replied, but it does back up what I said...the ground IS common.

 

Indeed. You ground through the bloke, or you ground through the block.
Common ground in either case.

-John.

 

i think i get it.......the primary coil is "charged" and then that circuit is cut and the secondary circuit is connected and the voltage is induced in the secondary and travels around the circuit. is that right? that scematic is what made me understand, im a visual learner.

 

The secondary circuit is always connected, but until it sees a high enough voltage to jump the spark plug gap, there is not a completed circuit.

But in effect, yes that's right.

John.

 

ok so i get it now. thanks so much for all your help

edit: maybe u can help with my overheating problem, check a few posts down

 

You're welcome.

By the way, the above diagram was taken off of the net just to show coil internals. Our coils are not wired anything like that one is. My FSM doesn't have a diagram so I'll repost one I had made a while back for a discussion in the 2nd gen forum. I should have posted it instead of the other one, as it's closer to how ours are wired:



-John.