Ignition coil: what does it do?

ok you Porsche nuts out there:

can you tell me what the ignition coil does?

I plan on replacing all my ignition wires this weekend along with distributor rotor and cap and was wondering whethere I should also replace the ignition coil as well.

thanks.

The ignition coil basically converts low tension 12v electricity into high tension, high voltage power to give you a nice juicy spark.

An old coil can fail but my experience is that they either give you all or nothing.

Why do you feel the need to replace all of your ignition parts - are you down on power?

Relacing all these parts may give you better performance - but I doubt it, unless they are faulty.

Just my 2cents worth.


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Alan Brown
86 Carrera 3.2

OK, the factory service manual calls it an ignition transformer, and it is, but with a special turns ratio and impedance to match the output of the Bosch CDI-system. The turns ratio is 1:100 nad it is specially designed to handle the 460 Volt output pulses, which are stepped up to 46 kV. Not the highest output around, but good enough for the factory to continue using the same coil as your SC uses until the end of '89 production on 930 Turbos! No need to replace your coil as part of a routine tune-up!
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Warren Hall
1973 911S Targa

[This message has been edited by Early_S_Man (edited 05-22-2001).]

Hello

Bassically the standard coil is also a transformator. But with 12 Volt and to achive a good power to volt ratio you have limitations. Also the unit musst hold the load until it is ueed so it needs charge capacity. This all leads to limitations and compromisses.

So the typical ignition flash is short and peaky. The coil uses the timeintervall for reload and those intervalls shorten with the engine rev.

Also the coil has the problem that the power that isnīt used to ignite the combustionchamber his to be transfered into heat and can not be used for the next spark.

This alll is like ligthening up a match in your combustion chamber.

The HKZ transformator just transformes the incoming voltage. thats it. Regulation is done by the CD unit and the spark is very digital. On/off.

Just like flashing a light bulb in your combustion chamber.

The HKZ is 4 times faster then the standard coil witch support high rev demands.

Also the "electric" speed from the unit is faster then the speed in typical combustion/sparkplug situations. So the power will not be drained by short circuits ( coal or wet spark plugs ).

The disatvantage is that the HKZ canīt be regulatet or prolonged. It is just like shooting something away. Maximum Speed and force. No way to control that.

But similar is with the standard coil. Its only slower and has less power.

Race units where also able to flash two or more sparks in short delay. But not all the time this was used to start up or at slow rev to stabilize idle and generate low end tourque.

This is where the newer TSZ cuts in. It just isnīt as fast like the HKZ but has a much longer flash time at the same curency level.
TSZ where later integratet in Motronic and had several stages.

Newer generations like Saab DI or Siemens PI units use the spark plug to feel the combustion demands and will spark on the spot with high currency or clean triggering or whatever the demand is. They also can ignite into the empty chamber to keep the spark plugs clean and they even have enough power to ignite a sparkplug without normal electrode.

Back to HKZ:

Well that 45 kV could have be higher but would have cost to much curency.

Voltage is nothing without the power to hold the spark stable burning a longer time.

Bosch had a just divided the curency to run into safe 9000/min. Back in 1967 this unit was the most sophisticatet and could only be found in the Ro 80 and Street sports cars ( Maserati, Lamborghini ).

Mercedes and some others used a simplier unit.

For race use Bosch made even beefier units that smaked up to 80 kV on a 16 Cyl with 10000 rev limit. Those engines had an own alternator for the secound ignition circuit.

A bit overkill for a street car but americans love high numbers.

16 Cyl didnīt made it as Piech had to leave the factory.

Grüsse

Hello

Bassically the standard coil is also a transformator. But with 12 Volt and to achive a good power to volt ratio you have limitations. Also the unit musst hold the load until it is ueed so it needs charge capacity. This all leads to limitations and compromisses.

So the typical ignition flash is short and peaky. The coil uses the timeintervall for reload and those intervalls shorten with the engine rev.

Also the coil has the problem that the power that isnīt used to ignite the combustionchamber his to be transfered into heat and can not be used for the next spark.

This alll is like ligthening up a match in your combustion chamber.

The HKZ transformator just transformes the incoming voltage. thats it. Regulation is done by the CD unit and the spark is very digital. On/off.

Just like flashing a light bulb in your combustion chamber.

The HKZ is 4 times faster then the standard coil witch support high rev demands.

Also the "electric" speed from the unit is faster then the speed in typical combustion/sparkplug situations. So the power will not be drained by short circuits ( coal or wet spark plugs ).

The disatvantage is that the HKZ canīt be regulatet or prolonged. It is just like shooting something away. Maximum Speed and force. No way to control that.

But similar is with the standard coil. Its only slower and has less power.

Race units where also able to flash two or more sparks in short delay. But not all the time this was used to start up or at slow rev to stabilize idle and generate low end tourque.

This is where the newer TSZ cuts in. It just isnīt as fast like the HKZ but has a much longer flash time at the same curency level.
TSZ where later integratet in Motronic and had several stages.

Newer generations like Saab DI or Siemens PI units use the spark plug to feel the combustion demands and will spark on the spot with high currency or clean triggering or whatever the demand is. They also can ignite into the empty chamber to keep the spark plugs clean and they even have enough power to ignite a sparkplug without normal electrode.

Back to HKZ:

Well that 45 kV could have be higher but would have cost to much curency.

Voltage is nothing without the power to hold the spark stable burning a longer time.

Bosch had a just divided the curency to run into safe 9000/min. Back in 1967 this unit was the most sophisticatet and could only be found in the Ro 80 and Street sports cars ( Maserati, Lamborghini ).

Mercedes and some others used a simplier unit.

For race use Bosch made even beefier units that smaked up to 80 kV on a 16 Cyl with 10000 rev limit. Those engines had an own alternator for the secound ignition circuit.

A bit overkill for a street car but americans love high numbers.

16 Cyl didnīt made it as Piech had to leave the factory.

Grüsse

so what does the ignition coil do again?

Performs MAGIC!

See, I knew you would like that one, better!

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Warren Hall
1973 911S Targa

Ever coiled up a hose? Well the ignition coil does the same thing to your ignition...At least that's what the guys at the pool hall told me!!!!!!

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Howie
79SC

Hello

Magic ? Donīt know how that double post happend mybe to much TTL ?

OK try to find a good description for average people:

I think I will stay with the waterhoses.
OK lets say your Car has a waterelectric.

The battery is a big watertank witch can suppley water in hughe demand and a fixed Pressure.

Lets say the pressure is 12 Volt äh bar witch equals a water hight from 12 meter.

Now you have a small watergun and try to shoot Blackbirds siting on the Thelegraphlines at 24 m. So you would need at least 24 bar pessure to give them cold feet.

How to get there ? Well you fill the gun and pump it to overpressure and then letz fezz.

Now back to physics:

If you have a basin filled with water and you have a tube upright on each side they will have the same waterlevel. Doesnīt matter what size the tube is. OK thats not exact as the smaller the tube the higher is the water in there. It will go abouve the normal level using the capilar effect.

The standard coil is like a big engine. You fill it and then the piston will push to the nozzle. And you can shot a load.

Now the HKZ works different. The unit just lifts a small amount of water far higher then the bird sits ( remeber the capilar effect ). Then you use the trigger and the small amont of water will fall down on your piston and using the velocity force to shoot an higher load then the normal version.

Well the ingeniuos trick on that is just to use the battery as the direct pump. And not to shoot on a "piston" instead to shoot away and use the vacuum to load the unit. This is why there is a big groundcable on the Porsche Coil. This is the direct connection to the battery and has to bear a hugher curency then the small cable coming from the CD unit. If you use a small standard cable you can see them melting away. The Coil also sees some ground via the housing but the higher resistance will lower output or generate sparks.

Generally all coils do not load a positive charge as the ignition spark must allways be negative ground ( On Negative ground cars, british cars ? well they use both ).

As you might remember from shool the potential is allways higher on - polarity and the ions move from - to +.

Thank god Volta was more theoreticall and didnīt like to guess like Farenheit so this "misstake" is easy to folow.


OK and now very short for the people who canīt follow my unfortunate try to explain physics without dictionary:


It is just like you compare Arrow and Bow with a Riffle.

I know the last is very easy to understand in the US. So I could have saved the first description. But maybe Warren would like to see that I have made my homework.

Think I can see a smile.

Grüsse

thanks to all for the in-depth technical knowledge regarding the ignition coil on my porsche 911




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83 sc euro cab

Let me try:
Your car needs power to start. Ordinarily, your alternator and battery provide power for your car, but the alternator/generator only works when the car is actually running and the battery isn't powerful enough to start the car on it's own. (It takes a lot of volts, and batteries provide only 12V - amperage is their strength). Your ignition coil is a power transformer that transforms (increases) the power generated by the starter motor (am I missing a step here?). The battery cranks the starter (which takes lots of amps, which is why the battery advertising mentions CCA - cold-cranking amps), the ignition coil steps up the power generated by the rotating of the starter (it's literally a coil of copper wires, like the tranformers power companies use to keep the power level even when transmitting it long distances using wires and cables). Anyway, your starter motor cranks the engine briefly, the ignition coil transforms this into a nice big shot of voltage, which then goes from the distributor (it's distributing power) to the spark plugs (hence the spark plug wires), which spark the combustion process, which drives the pistons, which cranks the cams, turns the crankshaft, etc. and the engine roars to life. The ignition coil then lets the battery take over the power duties, while the alternator keeps the battery replenished.

So, with a bad ignition coil the starter will crank but the engine won't fire because there's not enough voltage (or too little) reaching the spark plugs. The bad news: you usually work backwards to it when your car won't start. You check the spark plugs, the distributor wires, the cap, rotors, and distributor and once you've determined those are good...you check the ignition coil.

The good news: they don't tend to go bad nearly as often as the other items mentioned, so you've usually solved your starting problem before you get to it.

I think. (shop class was 20 years ago!)

Emanuel (hey, it may not be accurate, but gosh darn it, it's simple!)

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Emanuel Brown
1983 911 SC Targa
http://home.att.net/~epbrown01/91183.jpg

thanks Manny

your description was the easiest to follow and straighforward.

learning more and more on this board every day

Originally posted by 83 sc euro cab:
thanks Manny

See, you think I can get back at you for that, but I will. Some day, some how...
:-)

Emanuel

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Emanuel Brown
1983 911 SC Targa
http://home.att.net/~epbrown01/91183.jpg

Hello


>the ignition coil steps up the power >generated by the rotating of the starter >(it's literally a coil of copper wires, like >the tranformers power companies use to keep >the power level even when transmitting it >long distances using wires and cables).

>your starter motor cranks the engine
> briefly, the ignition coil transforms
>this into a nice big shot of voltage,
>which then goes from the distributor
>(it's distributing power) to the spark >plugs (hence the spark plug wires), which >spark the combustion process

>The ignition coil then lets the battery >take over the power duties, while the >alternator keeps the battery replenished


Are you sure about that ?

Grüsse

Roland,

I think Emanuel was polishing his skills as a comedy writer ... but, I might be wrong!

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Warren Hall
1973 911S Targa

Let's just keep it simple!
The two original replies from Alan & Warren really tell you all you need to know:

"The ignition coil basically converts low tension 12v electricity into high tension, high voltage power to give you a nice juicy spark." - Alan

"No need to replace your coil as part of a routine tune-up!" - Warren

Andy Boyle (UK)
'69 911E

I still dont really understand. But then my knowledge of electricity is virtually nothing.

Does a coil get a charge, store it until its big enough and then release it?

Can someone explain what tension is?

My knowledge is soooo bad I dont even know what amps and volts etc.. mean.

Can anyone explain electricity in an easy to understand and concise way?

And who said that English state schools are bad?!?!

Alex.

My Coil seems to be sufferring with the recent damp!.
Is this normal or is it on it's way out?
The car died 10 minutes after washing and then 3 miles out of town after an overnights rainfall on another occaision!.
New Coil?

Nope, I wasn't polishing my skills at comedy, just mixing up two systems :-) Like a said, high school shop was a while ago. Pretty much the only thing wrong, as far as I can tell, was the stuff about the starter motor since I conflated the two systems (ignition and starter). My reference on the subject says I got the rest of it right, though simplified: battery > ignition coil > distributor cap > spark plug wires > spark plugs. I skipped a bunch of stuff about resistors and breaker points and so on, but otherwise it seems close enough for government work.


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Emanuel Brown
1983 911 SC Targa
http://home.att.net/~epbrown01/91183.jpg

Since everybody has their own electron theory, let me offer you my interpretation:

The coil is a transformer, and as such it either steps voltage up or down. As an ignition coil it's a step-up transformer. There are two internal windings insulated from each other; the primary winding contains a few hundred revolutions of relatively large gauge wire. The secondary winding has many thousands of turns of relatively fine gauge wire.

During engine operation, system voltage (12V) via the battery/alternator through the ignition switch is applied to the primary windings then to ground through the ignition breaker points (a switch). During the time the points are closed (dwell), a magnetic field builds up around the primary windings much like an electromagnet. When the ignition points open, the magnetic field collapses which induces a high voltage in the secondary windings (which is connected to the distributor cap/rotor/spark plugs). This process continues each time the points close and open. A condenser (capacitor) is connected in parallel with the points to "absorb" the high energy voltage (self-induced in the primary windings) which provides a clean electrical break and reduces arcing.

As was mentioned previously, coil saturation (time to build magnetic field strength) decreases as engine speed increases. In addition, the point gap changes due to wear. This affects dwell and coil saturation. It also changes ignition timing. Dual point distributors attempted to increase the effective dwell period and increase secondary voltage. Still too much maintenance as points still wear.

To reduce maintenance and to increase engine tune, ignition points on late model vehicles are replaced by more reliable electronic devices (electronic switching) to build and collapse the field and higher primary voltages and multiple ignition coils to create higher secondary voltage

Hope this adds to the confusion
Sherwood Lee
http://members.rennlist.org/911pcars