Cliff's Notes on steriods

[ndutton]

I enjoyed a great email conversation with a forum member today discussing plans for his electronic ignition installation. He read all the threads he could find on the subject, spent hours doing it and came away on top of the subject (in my opinion) and confused (in his opinion). The truth is he knew a lot more about it than his confidence allowed.

He admitted it was an awful lot of reading, much of the salient points lost in the volume of material. Yeah I said, I know. We reduced the hundreds of posts and tens of thousands of words to this simple instruction when it comes to electronic ignition and the Atomic 4:

Add an $8 resistor if measurements indicate.

[hanleyclifford]

Volts = Amps x Resistance

We sure turned that into a major documentary.

[Tim]

Volts = Amps x Resistance or
Resistance = Volts/Amps

Hanley,

From the pictures you posted of your instrument panel you have approximately 11 volts at the coil + and around 1.25 amps. Does that mean the internal resistance of your coil is 8.8 omhs?

[joe_db]

FYI - when an engine is running, the ignition circuit is more complex than a straight DC current through a resistor circuit.
If you *really* want to find out what is going on, a voltmeter, an ammeter, an oscilloscope, and a rheostat would be needed.
For those that just want their engines to work the heavy lifting has been done for you

[hanleyclifford]

Volts = Amps x Resistance or
Resistance = Volts/Amps

Hanley,

From the pictures you posted of your instrument panel you have approximately 11 volts at the coil + and around 1.25 amps. Does that mean the internal resistance of your coil is 8.8 omhs?

I tested my coil for 3.7 ohms. The resister in front of coil+ tested at 2.1 ohms. I'm sure there is additional resistance in the circuit to and from the (dedicated) ammeter.

[hanleyclifford]

FYI - when an engine is running, the ignition circuit is more complex than a straight DC current through a resistor circuit.
If you *really* want to find out what is going on, a voltmeter, an ammeter, an oscilloscope, and a rheostat would be needed.
For those that just want their engines to work the heavy lifting has been done for you

I'm not much of a theoretician but I do want my engine to work, and work long time. That is why I do not allow more than 12 volts at coil+ and I regularly hold hands with my coil - the same coil I have had in cars over many years.

[Dave Neptune]

My thoughts

I personally feel this information is necessary but not only in "ignition trouble shooting", it should also be in "electrical or charging" as it is the upgrades there that have led to the "coil frying". I say this as I built an E/I for the first time I started my engine from being seized back in 1983. I built it out of a racing unit I was installing on modified Rotaries and 11,000 RPM's. I used the same basic unit that is the Indigo style (same manufacturer) with the huge dwell. I ran without a resistor and a stock coil for about 20 years and countless hours with no trouble at all. I then bought a new unit from Indigo just because of the LED indicator, so I just hooked it up and ran it. I stuck the old unit in the spares and ran the new one for about 7~8 years. I did upgrade my stock alt to 14.2 volts about 5 years ago and still no problems. After all of the problems showing up I contacted Indigo about 3 years ago and decided to see what the resistor would do or not do to my performance. I installed it and no difference at all other that a lower voltage to the coil, the beastie did not notice nor did I.
The above does not take the resistance and variations of old dirty, "stacked" power drains and corroded wiring!

I have now had 3 coils in 40 + years. The first was the original 8v rated with ballast that I never even tried, I just tossed the whole system. I built the shutter for the E/I and grabbed an old coil out of my spares and don't know anything about it other than it ran for many years until I bought the new Indigo unit that I bought with a coil. That one has lasted for many years and I have the old one as a spare.

Dave Neptune

[azazzera]

Please forgive me for this next comment but I can't resist.

Can someone who has Neil's number please call him an make a welfare check on him. It's been approximately 3-4 hours from Hanleys last post about coils and we have heard nothing from Neil. I figure he has been kidnaped or he is unconscious from blood lose from biting his lip too heard.

You have to give this one too me after reading there most resent skirmish.

Sorry.

[Tim]

I was only asking to further the discussion. The EI takes the 12 volts DC at the coil + and switches it on and off as the engine rotates. This switching on and off creates an AC signal. The simplified version of ohms law does not apply to an AC circuit with a coil. In this case:

Amps = Volts/Total Impedance

Impedance is the opposition to current in an AC circuit created by resistors, coils and capacitors and the units are in ohms.

Total Impedance = resistance + inductive reactance + capacitive reactance

inductive reactance is the impedance of a coil, capacitive reactance is the impedance of a capacitor.

So in Hanley's case there is 12 volts at the coil +, 1.25 amps measured, and the internal resistance of the coil is measured at 3.7 ohms.

1.25 amps = 12 volts/total impedance
total impedance = 12 volts/1.25 amps = 9.6 ohms
The internal resistance (as measured) is 3.7 ohms, so the impedance of the coil itself is 5.9 ohms.

In any case, Hanley's coil is providing 9.6 ohms of opposition to the current flow. That will vary with engine RPM because the inductive reactance of a coil changes with frequency.

[azazzera]

Ok I had my fun. Back on point. Thank you Tim for disrupting my already thin knowledge of the electricity stuff. I thought the positive side of the coil was were dc power went in to and the negative side saw a switching on and off. Guess I need more education on this one. I will read and re-read your post and try to digest. Google here I come.

[azazzera]

So when we are asked to measure the ohms across the posts of the coil this is not a constant resistance? It changes with Rpms? Is it that it just acts like an ac system. From what I know about it ac has a negative wave as well. Is that what is going on in the coil or is it more correct to think of it as an on off thing. Should this change anything about how to figure out how much resistance to put in front of the coil positive post.

[Tim]

You cannot measure the impedance of a coil with a typical multi meter. When you use a multi meter measure the coil, you are measuring only the internal resistor. A coil is nothing more than a long thin wire and has very minimal resistance. In a DC circuit a coil will simply be a short. However, when you apply an AC voltage to a coil an opposition to current flow is created by the magnetic field that builds and collapses as the current alternates.

[azazzera]

The more I read the more confused I get. I don't understand how an ac current is involved. As I understand it and I do use the word understand loosely dc current goes into the coil primary winding at the positive terminal and flows around a, always forget if it is a larger diameter wire with fewer turns or the other way around, an electric field of "force" is created. This field is made to collapse by the turning off of that dc current and a much larger current is created in the secondary winding and out the center post of coil. Do I have the very general idea correct. Coils have been called a type of transformer as well. Sort of the reverse of what we have on telephone poles. The talk of alternating currents confuse me. Is it true AC that if an ociliscope was used there would be a positive and negative deflection or I guess a sinusoidal (sp?) wave form.

Ok head hurts must rest. ��

[Tim]

You have the basics. The coil on your A4 is very similar to a transformer. And just like your coil, a transformer will not function in a DC circuit.
Here is how your DC becomes AC.
1) Approximately 12-14 volts DC is applied to the + terminal on your coil.
2) The - terminal is connected to the points in the distributor. (The coil is just a long wire and acts as a short until the current begins to alternate).
3) As your distributor rotates, the points close and shorts the circuit to ground.
4) When the circuit is shorted to ground, current flows and the voltage at the + drops.
5) As the distributor continues to rotate, the points open, the current stops and the voltage at the + terminal increases.
6) As this continues, the current continue to be turned on and off which creates an AC current.
7) If you have EI, the same thing is happening but the EI module is opening a closing the circuit instead of the points.

That it in a nutshell.

[ndutton]

Please forgive me for this next comment but I can't resist.

Can someone who has Neil's number please call him an make a welfare check on him. It's been approximately 3-4 hours from Hanleys last post about coils and we have heard nothing from Neil. I figure he has been kidnaped or he is unconscious from blood lose from biting his lip too heard.

You have to give this one too me after reading there most resent skirmish.

Sorry.

Hey, no problem. All is well here. From the forum FAQ:

the posts now appear as:

So . . . not my problem anymore. I've done my share, let someone else deal with it. This forum will be whatever you make it.

Here's a great place to start, Tim's post #14. You guys decide, true or false? If you deem it to be true, let it stand for future browsers to learn from and refer back to. If you deem it to be false, whatcha gonna do about it?