the secondary windings wire in an automotive coil has, i assume, two ends. anyone know what they are connected to?

i'm pretty sure one end is connected to the high-tension terminal on the outside of the coil (the one with a sparkplug type wire connected to it that runs to the top center of the distributor cap, but what is the OTHER end of the the secondary wire connected to?

just about everything is seen written and diagrams showing the inside of a coil is very, very vague on that. if i didn't know better, i might think that those authoring information on the workings of a coil, are so fascinated with the phenomenon of induction that they immediately center on IT, and never get around to where the other end of the wire goes. smh

...and WHY is it connected there, if one cares to expound on that too? thanks.

 

Here's an improved diagram with some proper "ground" symbols I added. (that's why they're a little wonky)



To answer your question, the other end of the primary windings are connected to the negative side of the coil.
Both the Primary and Secondary windings "ground" through the points when they are closed.

Keep in mind though, because the other end of the secondary winding is connected to the distributor cap rotor and thus, the spark plugs, no current is induced into the secondary winding yet from the primary winding to induce "spark"
This doesn't happen until the points open, thus, cutting the current to the primary windings.
At this point the secondary and primary windings are no longer grounded through the points.
So the coil has no choice to use its current induced into the secondary windings to jump the gap of the spark plug(s)

Note that where the primary windings are 3 ohm, no 1.5 ohm resister is used.
In a simple ignition circuit like this whet points are used, there has to be at least 3 ohms in the circuit in the primary windings, if there is not, the coil would over heat at idle and burn out.
The points stay closed longer at idle simply because the engine is running slower, this also saturates the primary windings with voltage, and if you had a 1.5 ohm coil with out a resister, this is almost like a dead short _ the coil wouldn't last very long.

A problem that had to be overcome with this is arcing at the points when they open.
When they open the cutting of the current causes the points "arc", so a condenser is used to prevent this _ like an electrical cushion.
That's why when the condenser fails, it shorts out the primary circuit OR it doesn't do its job anymore, and the points arc _ this causes the points to get black, and no connection is made when the points are closed.

 

thanks for the explanation Jeff.

if i remember correctly one side of the coil has two wires connected to it, and the other side has one. i'm pretty sure that on the side with two wires, one of them goes directly to ground.

... i've got to double check the wiring on my car...i'll get back to you.

 

checking complete...

so why doesn't the induced current (when the circuit is opened at the points) jump across the points rather than the spark plugs? after all, there are two gaps from which to choose: one at the sparkplug and another at the points.

is polarity at play here? or Lenz'a Law?

and why do the two sets of windings (i'm just asking the question and don't expect anyone in particular to know the answer) need to be connected? after all, the invention of the radio showed that a collapsing EM field can induce a current in a wire hundreds of mile away, without any contact whatsoever. is efficiency or longevity of the circuitry involved.

and why are the secondary windings grounded at all? to maintain persistence, maybe?

 

The coil is a transformer, so there has to be at least 2 winding for it to step the voltage from 12 volts to at least 40,000 volts.
If you took a coil apart, it would not look like the photo at all, that is just a pictorial diagram to show how things are wired.
There's an iron core in the centre, and the primary winding of thick copper wire with about 300 or 400 turns is would around that.
Then on top of that is wound the secondary windings of very fine copper wire with many thousands of turns.

When the points are closed, 12 volts flows through the primary windings and creates a magnetic field _ an electro magnet if you wish.
When the points open, the magnetic field collapses on the primary windings; and that collapsing then creates a new magnetic field (for a very brief moment) onto the secondary windings _ it's called induction.
It's this induction that creates the necessary voltage to jump the gap on the spark plug.
This all happens as fast as the points can open and close.

"So why doesn't the induced current jump across the points rather than the spark plugs"?

Because the points are just a switch that turns the cars 12 volts off and on to the coil _ the points are not a transformer.

"and why are the secondary windings grounded at all? to maintain persistence, maybe"?

They are only grounded when the points are closed, and it has to be this way for the coil to work.
When the points open, the secondary winding is then grounded through the spark plug(s) causing the high voltage to jump the gap.

 

This is not correct, the negative side of the coil does not have a wire directly connected to ground, if it was like that, nothing would work.
Wired up like that would by-pass the points and there would be no spark at all.

Look at my diagram again, even though it looks like the negative side of the coil is directly connected to ground, it isn't
The letter "B" says that's where the points should be.
The coil is connected to ground through the points _ the points are the switch that turns the coil off and on.
I'm not sure what those 2 wires are doing at the coil, but I know one will be connected to the side of the distributor, and from there it goes to the points.

On the positive side of the coil it may have 2 wires.
One may by-pass the ballast resistor from the starters solenoid so the coil receives a full 12 volts while cranking.
Once the car starts, the solenoid is switched off and the other wire takes over that has the ballast resistor connected to it; this is for for normal driving.

 

they may be no longer grounded through the points, but neither are the secondary windings grounded through the spark plug, both gaps present an equal opportunity for grounding. and so the current would appear to have a choice to travel in either direction. doesn't it? i.e. travel from the secondary windings to the sparkplug and jump the gap there to get to ground or travel from the secondary windings to the points, and jump the gap there to get to ground. i'm curious as to WHY it travels in the direction it does, seeing as how it could go either way.

i'm also curious as to the necessity and/or purpose of the connection (now that you've been kind enough to verify it in your diagram) between the two sets of windings. although i may have found something may shed some light on both queries.

...wondering if this bit of information i recently ran across while doing a bit of research that MAY be applicable in both instances, from: https://www.toppr.com/ask/question/an-induced-emf-has/

"From Lentz's law, the direction of induced emf in a circuit is such that it opposes the magnetic flux that produces it.So, if the magnetic flux linked with a closed circuit increases the induced current flows in a direction so as to develop a magnetic flux in the opposite direction of original flux.

If the magnetic flux linked with a closed circuit decreases then the induced current flows in the same direction of the original flux. So, the induced emf has not (sic) direction of its own.".

 

To discharge the secondary across the contact breaker gap, the current still has to flow through the spark plug.

When the contact breaker opens, it may appear that there is no return line from the ground to the secondary winding of the coil. In fact, there are two routes from ground to the secondary, one via the capacitor and one via the the battery and primary. This results in an oscillatory decay of energy from the secondary.

I suspect that battery ignition circuits evolved as much as they were designed. It's not usually recognised, though it's essential to the function, that the initial breakdown of the spark gap is due to the discharge of stray capacitance across the gap. If you design a system that eliminates all the stray capacitance (it takes some effort and would be extremely difficult with a practical engine and spark plugs), it becomes difficult to break down the gap.

 

There is such a thing as Back EMF.

 

Peter is spot on as usual. I was answering Huey.

 

i may be misunderstanding your sentence: "In fact, there are two routes from ground to the secondary, one via the capacitor and one via the the battery and primary.".

i can understand that the capacitor offers current a type of path to ground, but it too has a gap...

and i don't understand the phrase, "...and one via the battery and primary", although i agree as your diagram shows, that there is a path to the battery, it's not to the GROUND side of the battery.

as far as i know DC current only runs in one direction, so the current from the secondary windings is either running down the wires to the sparkplug or to the points/capacitor. my curiosity is leading me to ask why it chooses to run to the sparkplug in lieu of the points/capacitor route and jump to ground there. and why the two windings are connected?

but i'm onto something WRT to the direction of current flow from the secondary windings. i'll need to check a few things...

 

after a quick check, i think i have reason to believe (subject to contrary evidence ) i've found the answer to current flow and its direction in a DC circuit WRT an induced current. it appears the the direction in which the secondary windings are wound around the metal core of the coil determines the direction of current flow from the those windings.

and another source spoke to my other query regarding the purpose of the connection between the primary and secondary windings.

it appears that the primary windings wire and the secondary windings wire are connected together and wound around the same core to simply enhance the induced voltage in the secondary windings and, in turn, enhance the quality of the spark produced. IOW its an efficiency thing.

 

How about a link to some competent reference material.

 

IMO competence is much in the eye of the beholder, but here's what i used, in part, to come to my conclusions:

WRT to direction flow of an induced DC current, there's this:

https://en.wikipedia.org/wiki/Lenz%27s_law

and this:

https://en.wikipedia.org/wiki/Flemin...ule_for_motors

WRT the purpose of connection between the primary and secondary windings...

a quick google of "why connecting the primary to secondary windings in a coil improves spark" gives a bit of insight that was not available to me prior to google's implementation of AI about a year or so ago when i first brought up these issues in another automobile forum. the words and their order are important as one might guess. noodling/googling around with the words and their order may provide other, and possibly contrary, information.

 

Sorry, I don't know of anything very good that is dedicated to the conventional battery, coil and contact breaker system. The systems that I made (about half a century ago so I don't remember them all that well) used large, high voltage capacitors with the discharge controlled by triggers. They made nice, repeatable, close to square-wave sparks so it was easy to adjust the energy and duration.