My car's notorious for odd start issues when its warmed up. 383 stroker, hei with msd ignition and a coil mounted on the fire wall. Anyway, I just moved my coil away from my tach wires because I was getting weird tach readings now and then. I am almost certain than the (+) and (-) wires on the coil were backwards when I removed them to relocate the coil. I have since moved the coil and put the wires as they were supposed to be

Is it possible that the car could have run like this? It would have been like that for at least a year or more and once the car was started it ran perfect with dead-on perfect timing. Or am I mistaken about the wires being backwards?

I could be wrong here, but the pos and neg sides of the coil ...IF a car's coil is the same as other transformers, it shouldn't matter much, but I'm not sure if things are different on a car's "coil"...which is really a transformer. They do put on the coil which side you hook up, so it may matter.

If I am right, the pos is the 12 volt input which passes current through the primary coil windings to the negative side, which should eventually reach ground, but perhaps through a tachometer etc. first?

The only reason you don't have a direct short here is that the coil windings absorb the energy of current and pass it on to the other side of the transformer through a "magnetic flux". Remember also that the points, or whatever replaced them, are opening and closing at a fairly high rate, so this current rises and falls to help pass the energy over to the high voltage side of the transformer windings.

The advantage your 12 volt system has is that it can deliver one heck of a lot of current, even though it was low voltage. The coil trades off the power of the current for the increase in voltage in order to jump the spark plug gap.

So while it puts out a ton of voltage out of the coil, it's at low currents. That's why you can get zapped by a high voltage spark plug wire, but there's not enough current behind it to kill you.

Half asleep Steve

Automotive coils are not transformers, just a single coil winding. I got yelled at once suggesting that it was 'like' a transformer.

was told that sometimes the spark, if coil is reversed, jumps backwards on the spark plugs but the cars still runs because the cylinders fire in the same order. I don't want to reverse my coil to test it.

I've been chasing a hard start issue for years, this adds 1 more thing to the mix. I would think that even if the spark jumps the wrong way on the plug it wouldn't matter....the cylinder gets it's spark. Fire is fire, no?

I should ask my question on a site where people know less about cars because they'll tend to make more mistakes like this.

Yes indeed, it does matter.

The coil will still deliver a spark, but a very weak one.

As to the spark jumping "backwards", switching the coil primary wires wouldn't do it.

I believe that would occur with a positive ground system.

thanks. So I at least know that the car could run, and probably did, backwards. The MSD box probably gave me enough spark even reversed?

I remember this coming up once also in class one night and the instructor who said it was not a transformer got quite an education from one of the guys who was an electrical engineer! Everyone at the shop was required to attend this class because the company paid for it and the shop was shut down for the night so Slim (the electrician) got stuck with sitting through it even though he was way over the instructors head. An automotive coil is indeed a transformer (usually with just one winding however) and the basic function is the same as an AC transformer, that is to transform low current into high voltage in this case. Since current needs motion for a transformer to work you need a way to pulse the current when using DC, in this case the points or solid state system to break the ground to provide the collapse of the current to induce the secondary voltage. This is accomplished with the 60 cycles per second reversal of polarity with AC current. If an ignition coil is not a transformer just what the heck is it?



Correction!


That is to transform low voltage high current into low current high voltage, NOT low current to high voltage!

Transformers work by inducing current into a secondard winding that passes through the magnetic fields created by the alternating current. Alternating current is the 'motion'. DC, fixed current.

DC coils, when switched off rapidly, just create that voltage 'spike'. Cars use that for spark but something like a TV or stereo system (that uses a relay or 2) also makes the same spark which can burn out your system so they put components in to absorb the spike.

Yes, a coil is transforming low DC into high DC but I think it fails the definition of a transformer.

Sorry to drag this out.

I got curious and checked this out, not trying to argue I was just curious, and everything I found on the net describing an automotive coil calls it a transformer. I was also under the impression that most ignition coils used just one winding but I discovered that it is the other way around and most use two windings just like a regular AC transformer.

When I reread my post I found made a serious typo in describing the function of a transformer in that I said it changed low current to high voltage!

I guess this is another solenoid/relay controversy!

This is the first 6 links that Google listed and I checked several more all of which describe the coil as a transformer and working like a transformer, I did not see any that said it was not a conventional transformer. Apparently somebody was way out of line when they yelled at you because you were right and they were wrong!

http://auto.howstuffworks.com/ignition-system3.htm

http://news.carjunky.com/how_stuff_...ks_ic2315.shtml

http://mgaguru.com/mgtech/ignition/ig108.htm

http://www.type2.com/library/electrip/ignwor.htm

http://www.sentex.net/~mwandel/cannon/sparky.html

http://www.members.shaw.ca/forcelabs/IgnitionCoil.htm

Whom-ever told you that is wrong. An automotive coil consists of two windings a primary that's being switched by whatever is in the distributor using from 9 to 12 volts and a secondary winding that delivers several thousand volts. Both coils are wrapped around a soft iron core. The collapse of the magnetic field generated by the primary winding when it's switched off causes a voltage to form in the secondary coil which is connected to the spark plugs via the distributor in older systems.

The primary coil has several hundred loops of a large size wire, the secondary winding has thousands of loops of a much finer wire. In simple terms the ratio between the windings establishes the difference between the voltages of input to output. It's actually stickier than that but the point I'm trying to get to is that an ignition coil most certainly satisfies the definition of a transformer.

This isn't any different than how gear ratios work. In a similar case to the coil high torque at low speed goes in one end and low torque at high speed comes out the other in the case of a step up gear box. For a step up coil the same thing happens; high amperage at low voltage flows into the primary winding and high voltage, low amperage flows out of the secondary winding.

Modern ignition systems are doing the switching with transistors that are under the control of a computer, but that hasn't changed how a coil/transformer works. Capacitive discharge systems just put a capacitor between the switch and the coil to give the coil's primary an extra voltage jolt which makes a faster forming and stronger magnetic field so when it collapses, the coil delivers a higher output voltage.

Bogie

That was my take on it too and it would seem most coils are two windings, I would assume that if you attached 12 volts AC to an ignition coil you would get a continuous (60 cycles) alternating polarity spark? The single winding coil is somewhat of a mystery to me, I have heard it described as a single winding with a solid core and taps? Any idea how this works?

To answer the original question, yes it will work if connected backwards but it will not work correctly. The design is for the current to flow in 1 direction and for the circuit break to be on the negative side of the coil. If wired backwards in a points type ignition it will almost act like a flaky condenser.

__________________
Artificial Intelligence is no match for Natural Stupidity



Chet

guess I should have googled before posting my 'mistaught' coil theory. It's been described to me as 1 continuos coil winding with a 3rd connection for the spark-distributor wire. One of the links above does show the 2 windings connected end to end , but that's still 2 windings I suppose.

A final question which I'm thinking is answered by the fact that my car is still runnng: reversing the coil shouldn't have affects the MSD boxes, right? I still appear to be getting a good spark

Well that probably explains the "taps", a positive, a negative and the spark plug connection. I have heard an ignition transformer described as one winding with a solid core and three taps but it really did not make sense because "taps" are different points to take different voltages off of a multi-tap AC transformer. Got my curiosity going now (it don't take much to entertain me these days ) so I will try to find out what it is, I think even one of the links I found calls some of them single winding.

I'm thinking most coils are two windings, because the makers uses specs like 70:1, 85:1 and 100:1 turns ratio.

I've always heard of coils being transformers, too.

This is from Wiki, on transformers:

"A varying current in the first or "primary" winding creates a varying magnetic field in the core (or cores) of the transformer. This varying magnetic field induces a varying electromotive force (EMF) or "voltage" in the "secondary" winding. This effect is called mutual induction."

Sure sounds like a coil to me...

I can't find a thing on "single winding solid core" transformers other than just a couple of vague descriptions of automotive coils. Oh well maybe someone will see this thread and be able to explain it.



Gosh I sure miss Doc, I bet he would have gotten a good laugh at this thread!

(Not the original question, that was a good one, but the mystery about the single winding coil.)