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Sun Mar 21, 2010 3:23 pm

I never understood why the 1 and 15 terminals on the coil were supposed to be connected in a certain manner. It seemed to me that the purpose of the coil was to transform 12V to 18,000V and it didn't make a difference how it was wired as long as the current went through it, multiplied, and went to the plugs.

I found this info in the "Road Baron tm a service/repair handbook for Volkswagen"

"Spark Polarity

Less voltage is required to cause electron flow from a relatively hot electrode to a cooler one. Since the center electrode is hottest, this electrode should be negative. Electron flow is then from the center electrode to the outer electrode. From 20% to 40% more voltage is required to cause electron flow from the outside electrode to the hottest center electrode. This occurs when the spark voltage is positive.

The coil must be connected so that the double wire (from the battery) goes to terminal 15 and the single wire (from the distributor) goes to terminal 1. This ensures that the spark will be negative."

At one point in time my coil was connected backwards, but a VW mechanic noticed it and switched to the correct configuration. I never noticed a difference in performance but now I know there is a reason.

Hope that this is interesting and/or helpful and is a thank you to those that have replied to my questions and have been helpful to me with their replies, knowledge, and opinions.

Aloha
tp

Sun Mar 21, 2010 3:54 pm

The pencil test:

Sun Mar 21, 2010 4:06 pm

Please be sure to hold the pencil by the wood.

Sun Mar 21, 2010 4:22 pm

Mal evolent

never heard of the pencil test before
thought I got some book learning today and would pass it on, but now my knowledge has increased exponentially

thanks for your post
and for making me a bit more knowledgeable
what can we do about wiser and smarter?

Aloha
tp

Sun Mar 21, 2010 4:42 pm

There is more to it than the polarity of the spark. The high tension circuit in the coil needs a second connection "or ground" to work correctly. If you look at the schematic you will see that this second connection is through the #15 circuit. If you hook the coil up backwards the second connection is going to be through the points and condenser instead (or the electronic ignition module) so the inductance of the circuit will be affected. Especially in the case of an electronic ignition module you may be getting some very high voltages in a place not designed to handle it as well.

Sun Mar 21, 2010 7:24 pm

the coil is in fact two coils on a common core.

one coil has relatively few windings of large wire. this coil connects to the battery on one side. the other side connects to the other coil, and the points. this primary coil is wound around and encases the secondary coil.

when the points are closed a current flows through the primary coil causing a magnetic field to build around this primary coil. when the points open, said magnetic field collapses. the inward rush of the collapsing field is a magnetic field in motion. the field collapses through the secondary winding. this generates a small current at a horrendous voltage in the secondary windings. ergo, a spark at the plug.

note that the spark occurs when the points OPEN.

the capacitor - usualy called by the century old out of date term condenser in the automotive world - keeps the points from pitting. it absorbs the current surge that would burn up the points when they just start opening.

Click here to see an illustration

Sun Mar 21, 2010 10:30 pm

When Ben Franklin proposed his theories of electricity he had a 50/50 chance of getting the direction of the flow correct. He proposed that the flow of particles was from positive to negative. Since then we have learned that the flow of electrons is from negative to positive and that it is not a good idea to fly a kite in a thunderstorm.

I knew that the spark occurred when the points opened and that an automotive condenser is a capacitor and that a bad one would cause the points to become pitted. Now I know why.

Thank you Mal evolent
Aloha
tp

Mon Mar 22, 2010 7:10 am

Sure, we could stop dictators and pandemics, but we could also make the signs on every damn diagram make sense.

that said, wildthings noted the second problem with a backwards coil before I could, there are 4 wire ends in that coil, and only 3 terminals, obviously 1 is shared so there is little room for musical chairs here.

Tue Mar 23, 2010 7:15 am

Mal evolent wrote:
the capacitor - usualy called by the century old out of date term condenser in the automotive world - keeps the points from pitting. it absorbs the current surge that would burn up the points when they just start opening.

Click here to see an illustration
In electronic terms the coil would be called a pulse transformer. I guess "coil" is easier for us automotive types! 8)