Ignition system - how does it work?

[Donald H.]

My question is probably covered elsewhere, but I couldn't find a specific answer by searching.

I'm trying to understand what happens and how it happens with the ignition system (diagram attached) when the engine is not running versus when it is running. I did some testing on my 67 to try and understand and what I think I found is as follows:

With the key in the ON/Run position, the IGN position of the ignition switch is connected to power and this energizes the ignition system. When the engine is not running, I measure 12.49 volts on the coil side of the ballast resistor and 12.41 volts on the IGN side.

I had assumed that even with the engine not running I would see a voltage drop when measuring each side of the ballast resistor. But that is not the case.

With the key turned to the Start position, the SOL terminal on the ignition switch is also connection which energizes the starter via the 'S' terminal on the solenoid and the engine starts. With the key back in the ON/Run position, and the engine running I measure 9.8 volts at the coil side of the ballast resistor and 13.8 volts on the ignition side.

I think the 13.8 volts is simply the charging voltage, but what I don't understand is what happens in the ignition circuits when the engine is running versus when it is not running at the ballast resistor?

[Richard M.]

Re: Ignition system - how does it work?

Don, When you measured key in RUN, you saw no voltage drop because the distributor ignition points were not closed. You'll see the voltage drop if points are closed.

Rich

[Donald H.]

Re: Ignition system - how does it work?

Thanks Rich.

I did find a YouTube video of a guy with an ignition system set up on a bench, including distributor and when you rotated the distributor between opened and close points the voltage would drop.

Not a big deal because it works, but I just can't figure out how it works. I assumed when I measure voltage on the ignition side of the resistor that I would be getting full battery voltage, which I do. But I was expecting to see reduced voltage on the coil side of the resistor because I though I was measuring voltage after it passed through the resistor.

I just don't understand how the current flows, i.e. path, through the ignition system.

Don

[Richard M.]

Re: Ignition system - how does it work?

Don, I'm no ignition expert but I'll try to describe the way I understand it....

The points are a simple switch from coil- to ground. When the points close, the ground path to coil- is complete and there is now a current path through the ballast and the input of the coil+, back to ground. The coil+ always has power(in RUN, ENGINE running) and the switching is done via the points to ground on the distributor breaker plate, which is grounded to the distributor/engine ground.

With the points closed there will now be a voltage drop across the ballast resistor, as well as current flow, because the circuit is now complete and the ballast output will now be a lower voltage. There will only be a voltage drop across the ballast when points are closed, i.e. coil- grounded. The lower voltage from the ballast output is then applied to the coil+ and current flows through the coil primary side transformer and builds a magnetic field.

The coil is a basic "step-up" transformer with low winding wire count on the primary(+ & -) and very high winding wire count on the secondary(high voltage wire) side. A low voltage in will yield a high voltage out.

When the points open the magnetic field collapses and the secondary transformer creates the high voltage to the spark plugs, terminating now to the shortest path to ground, the engine ground. The distributor condenser quickens the coil field collapse and also helps to reduce points arcing to prolong contact life.

Of course, all of the above happens in milliseconds and then repeats.

Rich

[Donald H.]

Re: Ignition system - how does it work?

Your a pretty good expert as far as I'm concerned!


Thanks,
Don

[Carl S.]

Re: Ignition system - how does it work?

Rich,

Thank you for the amazing explanation which I read several times trying to wrap my mind around it. A question though . . . Since I have the K66 transistor ignition on my car (67 L71) does the TI take the place (electronically) of the opening and closing of the points? i.e. the TI functions via electrical circuit instead of mechanical points opening and closing? Thanks for your many posts and replies. Excellent information. C.J.

[Richard M.]

Re: Ignition system - how does it work?

Rich,

Thank you for the amazing explanation which I read several times trying to wrap my mind around it. A question though . . . Since I have the K66 transistor ignition on my car (67 L71) does the TI take the place (electronically) of the opening and closing of the points? i.e. the TI functions via electrical circuit instead of mechanical points opening and closing? Thanks for your many posts and replies. Excellent information. C.J.

CJ, I'll try to give my interpretation below....

Yes, the electronic switching function of the TI system was designed to replace the mechanical switching in the standard ignition system. However, a few circuit path differences. In particular, in the 1966 & 1967+ TI system, the coil- is hardwired to chassis ground and the coil+ is switched on and off via the TI circuit. Earlier(1964/1965) TI systems were wired differently. Diagrams below.

The electronic switching actually begins inside the distributor, like the "points" system does, but is certainly more complex. It is made up of a rotating disc(pole piece) with 8 physical protrusions positioned in it's outer diameter. A special "Pickup"(PU) coil is mounted within a magnet, and it also has a stationary disc with 8 protrusions on it's inner diameter. Photos below. Basically this internal PU coil and magnet acts much like a DC generator, generating a output voltage when the internal pole piece rotates via the distributor shaft. This PU coil is powered by 12 volts, through a resistor wire, when IGN is on. Note that during START(Crank), the Solenoid R terminal supplies full battery voltage to this PU coil, as well as the TI Module, bypassing the resistor wire. NOTE: Full voltage is NEVER distributed directly to the Ignition coil+ during Crank in the TI ignition system.

As the distributor rotates, each of the 8 rotating points passes by their matching magnetized stationary points. Note these points never touch each other. Each time these "pointed" areas pass each other, the PU coil generates a low voltage pulse(less than a few volts DC). Also note that each stationary point coincides with each spark plug position with respect to the distributor Rotor tip in the distributor cap. At each of the 8 cycles, this pulse is then sent to the TI Module via the TI harness. This is called a "trigger" pulse.....Trigger meaning as it implies, ready to trigger or "shoot". The TI distributor has a 2 wire connector to connect to the PU coil. One PU coil wire is +12V in(WHITE), the other is the low voltage pulse out(WHITE/GREEN, or GREEN).

Inside the TI module are several transistorized switches. The first transistor switch takes each low voltage "trigger" pulse from the distributor, then amplifies it through 2 very high power transistors. The final output transistor then generates a high current, higher voltage equivalent timed pulse. This high power DC pulse then traverses through the TI harness, via a low ohm resistor wire, directly to the Ignition coil+ terminal. The resistor wire acts much like the ballast resistor in a standard points system. This lowers the voltage to the Ignition coil to prolong its life. Note the earlier 1964/1965 version placed the resistor wire in the coil- (ground) path of the circuit.

As this high current pulse enters the Ignition coil+, it acts much like the standard ignition system from here onward. When the pulse stops at the trigger point in the distributor, it then shuts down the TI Module transistor pulse. At this point the Ignition coil magnetic field then collapses and generates the high voltage pulse to each spark plug.

The TI system was designed to outperform the standard points ignition system, to eliminate mechanical switching limitations and to provide higher coil output spark voltage for increased ignition performance at any engine RPM. When it's working properly it's a great system. When it breaks, it can be a bit tricky to diagnose. There are some helpful diagrams and troubleshooting documents that can help(attached below). The new TI circuit modules are a big improvement over the original AC Delco circuit boards. I always recommend to carry a spare TI Circuit board as insurance.

Rich




Pickup coil and stationary pole piece(stator). Held together over round magnet.



Rotating Pole Piece attached to shaft.




Note polarity of wiring at connector.







66-71 (1).pdf

64-65.pdf

[Chris H.]

Re: Ignition system - how does it work?

Thanks Rich, very informative. Do you have a preferred supplier/ vendor for the TI circuit modules? Chris

[Carl S.]

Re: Ignition system - how does it work?

Rich,

An amazing in-depth explanation to be sure. Thank you very much for the detail which will indeed be a lifesaver if my (or anyone's) TI system is ever in need of troubleshooting. Thankfully all is well for now. Excellent layout!

C.J.

[Richard M.]

Re: Ignition system - how does it work?

CJ, Glad it helped. I had to refresh my memory of it's operation so was good for me too.

Chris, I prefer the K & B circuit board. Many vendors sell it or you could get it directly from K & B.

Here are some links to more information for reference.

AC Delco circuit troubleshooting and wafeform analysis...

https://www.forums.ncrs.org/showthread.php?113103-K66-Transistor-Ignition-Delco-Circuit-Module-Failure-Diagnosis-and-Repair&highlight=transistor+ignition

K & B Board replacement...

https://www.forums.ncrs.org/showthread.php?115755-Installing-a-new-TI-board-in-the-amp&highlight=transistor+ignition

Rich

[James G.]

Re: Ignition system - how does it work?

CJ, Glad it helped. I had to refresh my memory of it's operation so was good for me too.

Chris, I prefer the K & B circuit board. Many vendors sell it or you could get it directly from K & B.

Here are some links to more information for reference.

AC Delco circuit troubleshooting and wafeform analysis...

https://www.forums.ncrs.org/showthread.php?113103-K66-Transistor-Ignition-Delco-Circuit-Module-Failure-Diagnosis-and-Repair&highlight=transistor+ignition

K & B Board replacement...

https://www.forums.ncrs.org/showthread.php?115755-Installing-a-new-TI-board-in-the-amp&highlight=transistor+ignition

Rich

I heard that DAVE FIEDLER, long time owner of TI SPECIALITY in Richmond, Indiana is for sale. He is retiring. 1-765-962-4265.