Technical So, give this a think

I know how an ignition system works, of course we are talking about point systems. BUT, we all know that it takes a complete circle of conductors for current to flow right? so take a look at an ignition coil, see how it is not grounded? And the secondary winding is connected to the primary winding on one end while the other end goes to the plugs. so knowing we need the complete circle for the current to jump the plug gap how does the other end of the secondary connect to ground? I see three possible ways, one through the primary winding and through the condenser (remember the points are open when the spark accrues) But I don't think you would have the high voltage jumping across the "plates" in the condenser as that would damage it. SECOND way, maybe it also jumps the gap at the points, I know when you open the points it makes a spark but I think that spark is from the current feeding the primary winding. So I don't think that is it. Third possible way, The current goes through the primary wire, through the key switch and to the battery, then across the battery and to ground. But once again I don't think so.
I have see very old schematics of ignition coils that have the one end of the secondary winding grounded to the housing of the coil but anything newer (newer than 1920's or so) has the one end connected to the primary and nothing grounded. In fact, you don't need the coil grounded for it to work.

 

Start thinking current, then think electromagnetic field, then think voltage. While the points are closed, constant current flows through the primary coil. When the points open, the current changes very quickly, it is no longer constant. The primary and secondary windings form a transformer, or in this case where the windings share a connection, an autotransformer. Fast-changing current in a coil of wire causes a voltage V= L di/dt, where L is the inductance of the coil, and the secondary winding multiplies this voltage by the turns ratio. The secondary voltage continues to rise until it reaches the breakdown voltage of the spark gap. The spark gap is a complex thing to model electrically, but we can simplify by thinking of it as starting like a capacitor with a voltage-controlled switch, initially opened. The cap voltage builds up until it reaches the switch limit, then the switch closes and current flows across the gap to ground. Eventually (which is a tiny fraction of a second) the field generated by the falling current in the primary cannot sustain the arc, and the spark goes out.
Yeah, that was a wayyyyy oversimplification of spark gap. Doctoral theses have been written on modelling the good old Kettering ignition.

 

WOW!

 

The very simple answer is the spark plug is the ground for the secondary side.

 

Owww ... my poor little think.

 

The battery provides the ground on the power side of the coil.

 

Good expiation of the importance of polarity

 

Expiation??? I think your fingers went dyslexic there for a moment.

 

Started out learning about points and learned a new word, only on HAMB lol
Dan

 

When I was still working I was amazed how many young electricians and electronics techs thought that the coil fired when the points closed , I wish I had that literature, I couldn’t make them understand the coil field collapsing.

 

I just turn the key... LOL

 

Make and break, baby!

Chris

 

But what is the current flow through the complete secondary? I understand how the secondary current is developed, I'm just trying to get my head around the flow of this secondary current.
Very old ignition coils have the secondary winding grounded inside the coil housing and in this arrangement I understand the current flow. In more modern coils (after mid '20's or so) the secondary is connected to the primary winding. My thinking is this is done to take advantage of the primary windings to add to the voltage for a better spark. And Wanderlust's post confirmed this, it adds about 200 volts to the output.
Think of it this way, to get a light bulb to light you need a complete circle or circuit for the electrons to flow from source (battery) to load (light bulb) and then back to the source. In the secondary of the ignition coil, with one end of the winding connected to the primary, what is the circuit? If the secondary winding is the source and the spark plug is the load how does the current get back to the source? I understand the spark plug is grounded and so is the battery but the current generated in the secondary is not ground based, does not connect to ground, unless the secondary current travels through either the condenser, or the key switch and back to the battery.

I'm sorry I'm having a hard time putting in words my exact question.

 

YES but the secondary winding of the coil is not connected to ground. so what is the current flow?

 

Take a deep breath, add some brandy to your coffee, and accept the fact that it works

 

Well, this is true, and I don't have a problem with any thing I own. I have wondered about this since 1974....

 

I gave a complicated answer, 57Fargo said it simpler. Wanderlust's first attachment reminds us to think about current as flow of electrons; the coil rising voltage builds up electrons on the hot center conductor until there are enough to jump across to the grounded conductor.
The schematic you posted doesn't show an easy-to-understand path, like a piece of wire that can conduct DC current; the spark conducts current but its a dynamic, nonlinear, fast-changing current. Think of the medium in the spark gap as a really lousy conductor; where you just have the word SPARK above the high tension terminal, draw a wire going to the spark plug with its gap and the ground connection on the other terminal of the plug; then schematically draw a really lousy conductor, like giant resistance, across the gap. That schematic represents the points closed. Now lets slow down time...open the points, and as quick as you can, draw a piece of wire across the gap; that is the spark. Now as quick as you can, erase the wire; it conducted a whole lot of current in that short time, which is all we are concerned about. Okay, go ahead and speed time back up to normal.
There is still some residual stuff going on after the spark quenches, but its small, for this discussion I am just going to ignore it.
Hope that helps.

 

Should be something like this.

With point closed: power, primary winding, points, ground.

With points just opening: primary winding induces a large voltage in the secondary that is added to the circuit.

With the points open there is a path like this: power, primary winding, secondary winding ( the two windings are in series ), spark plug, gap, ground.

Once the spark occurs and before the points close, you essentially have an open circuit ( open switch ) at the spark gap. The normal 12v power source is not enough to jump the gap.

 

There's a missing element. It requires high atmospheric pressure to make the path to ground (spark plug) intense enough to light an air/fuel mixture. And it takes a shit ton of voltage (from coil windings) to jump to ground as well. For 500 bonus points how many amps does a coil use? Hint, not much. Volts are power, amps are volume.

 

It's all invisible and this discussion will go on and on with correct and incorrect replies.

 

The airgap between the plug center and finger gets ionized by the high voltage - thus creating a path back to ground. Does not need high pressure - only high voltage.

 

Let's see if I can clarify this...

Look carefully at the diagram...

Power comes in on the positive terminal, goes through the primary coil, and when the points are closed, out to ground via the negative coil terminal and points. This is when the magnetic field in the primary coil is made. A complete circuit. But the secondary side of the coil is also connected to that same 'grounded' negative terminal and the other end of it is 'open' (no power applied) so no voltage/current can flow.

The points open. Now both coil windings no longer have a ground through the points. The magnetic field in the primary collapses, inducing voltage in the secondary winding. This high voltage seeks a ground as it's still being 'pushed' by the power coming in at the positive terminal. It squirts out to the spark plug and jumps the gap. Once the magnetic field fully collapses, voltage drops off and the spark dies. When the points close again, the process starts over...

 

I’ve always thought (maybe wrong) the opening and closing of the points mimicked AC voltage so the coil to transform it to a higher voltage.
But I like @alanp561 ’s approach

 

With the exception of where the switch is in the circuit, your lightbulb circuit is a great way to look at it. When the points (wall switch) makes the connection, the juice floods the coil (lightbulb) creating a magnetic field (light), and it's grounded out the negative side of the coil. There is your circuit.

When the points open (wall switch turned off), the light goes out (magnetic field collapses), causing the surge to go out the frayed end of the cord into your hand (coil tower to spark plug), which shocks the hell out of you (engine fires)

-rick

 

I’ve never had a problem running points like the manufacturer set em up


Crazy. I know it

 

Yes but I'm asking about the secondary circuit