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AH 100-6 Ignition coil polarity POSITIVE EARTH

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ronzet

ronzet

Jedi Knight
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Good day. I am in bit of a quandry... I purchased a new coil for my 100-6 from Moss. The polarity on the low tension side of the coil is my problem. I have poured over all three of my schematics and read the dialogs to no avail. Ergo, can anyone tell me which of the poles (+ or -) on the coil is the CB (connected to the distributor) and which is the SW (connected to the switch)...keep in mind that this is a POSITIVE EARTH system... I already have conflicting views sooo looking for someone that REALLY knows FOR CERTAIN... If you have a 100-6 that is still positive earth, could you walk out and look under your hood to see if your coil has a + and a - on the coil and see which one goes where,,, Thanks soooooo much.. Ronzet
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Re: AH 100-6 Ignition coil polarity POSITIVE EART

It really isn't that difficult. Since the points (CB) connect the coil to ground (earth) -- on a positive ground car, the positive coil terminal (+) connects to the points (ground). On a negative ground car the negative coil terminal (-) connects to the points (ground).

On the older coils which were marked SW & CB, they were intended for positive ground cars, CB would go to the distributor points & SW to the switch. If you reversed the car's battery polarity using the same coil it would be connected oppositely.
D
 
Re: AH 100-6 Ignition coil polarity POSITIVE EART

Dave, Thanks for the guidence... Ron
 
Re: AH 100-6 Ignition coil polarity POSITIVE EART

Very interesting....... I had a similar problem when I finished the restoration of my 100. I stayed with positive earth and couldn't remember which way the coil was connected. I looked on the internet (before I found this forum) and found incorrect advice to hook the wires up with - to the contact breaker. The engine started and ran OK. When another club member called to ask this question of me I passed on the incorrect information. His car would not run so he tried it the opposite way. Hey presto his motor started and ran well. After suffering an occasional misfire and burnt points I swapped my own coil polarity to + to CB and cured the misfire. As Dave states, the rule of thumb is "CB = earth". Funny how my car worked though.
 
Re: AH 100-6 Ignition coil polarity POSITIVE EART

Pan,
Your experience is correct. Although many engines will run with either coil connection, some may not run very well.

The theory is that electrons flow from negative to positive & that electrons flow more easily from a hotter surface to a cooler surface. Remember the old vacuum tubes (valves). The cathode was negative with respect to the plate & was heated by a cathode heater.

Back to sparkplugs; When the coil primary terminals are reversed, it also reverses the secondary (HV) spark polarity. The center electrode is hotter than the ground electrode. It will be easier for the spark to jump from a hotter center electrode which is negative with respect to ground to the cooler ground, positive electrode.

A reversed coil connection would have the cooler (ground) electrode at negative potential & trying to fire to the hotter positive potential center clectrode.

It has been estimated & measured, that a plug with negative center electrode will require about 20% less voltage to jump the gap than if the spark's polarity is reversed. The polarities & voltage levels can be readily seen on a modern ignition scope analyzer.
D
 
Re: AH 100-6 Ignition coil polarity POSITIVE EART

Well, and thanks for that. Now that I have my electron 101 completed, LOL.

Really, thanks, most intresting.
 
Re: AH 100-6 Ignition coil polarity POSITIVE EART

A well timed thread for me. I just put a new coil in the Tunebug, and after reading this, went out and checked. Sure enough, I had it wired in backwards. Oops, and now corrected!
 
Re: AH 100-6 Ignition coil polarity POSITIVE EART

The last word on this subject? My misfire returned, and after reading Dave's detailed reply I replaced points & plugs. Misfire finally cured by replacement of the condenser. Perhaps the reversed electron flow damaged this item?
 
Re: AH 100-6 Ignition coil polarity POSITIVE EART

Most likely, a coincidence. The particular condensers used on these cars should not be polarity sensitive. It was probably ready to go anyway. Glad you found the problem.

Normally, reversed coil polarity would not cause a problem, if the rest of the ignition system was in top condition, everything properly set, & the engine was not under heavy load. Wider than normal plug gaps "could" cause a problem, & as you see, a good condenser is necessary also.

It's just that with reversed coil polarity there is not that extra margin to cover less than optimum conditions.
D
 
Re: AH 100-6 Ignition coil polarity POSITIVE EART

Once had a prob with a capacitator/condenser being fitted to wrong side of insulator, wouldnt work till you got the revs so hi you were bouncing the points, was a triumph herald with an mg motor in it
 
Re: AH 100-6 Ignition coil polarity POSITIVE EART

Well Pan. I don't think reversed electron flow had any part in the failure.However,based on your earlier testimony of having the coil polarity reversed. You just may have exceed the old capacitors working voltage since this wrong way around created a secondary voltage that is about 25 % higher than is normal.--Fwiw---Keoke
 
Re: AH 100-6 Ignition coil polarity POSITIVE EART

The coil is simply a transformer that converts one pulsing voltage,(12V pulsing due to the opening of the points), into a higher voltage pulsing DC output. Since it is really a pulsing DC output, ( not a pure AC sine wave ), one or the other ends of the spark plugs act as
a cathode emitter. It is therefore important that the electrode that was designed to be the emitter be used as such. The threaded end is designed to be the anode ( collector ) and to dissipate the heat energy. If it were a pure AC signal going into the coil, instead of the pulsing DC, then it would not matter about the polarity as both electrodes would take turns being first the cathode and then switching over to be the anode in the bottom portion of the sine wave.....
The reason I posted is that the output from any coil or transformer is the same, no matter what polarity is put on the primary side. The polarity has no effect, one way or the other, on the output of the coil or any kind of transformer.
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Re: AH 100-6 Ignition coil polarity POSITIVE EART

Nope Ed that is not the case but I do not care to push it.---Keoke
 
Re: AH 100-6 Ignition coil polarity POSITIVE EART

The capacitor actually acts like a “shock absorber”. The problem with foil and wax-paper wound capacitors; they will “dry out” over time resulting in failure. This will happen to older capacitors either sitting on the shelf or in service. That being said, caution should be used when purchasing new capacitors setting on the parts self for many years. This makes a better case for converting to an electronic ignition.
 
Re: AH 100-6 Ignition coil polarity POSITIVE EART

OK... I guess we will just have to agree to disagree about how transformers work....
 
Re: AH 100-6 Ignition coil polarity POSITIVE EART

That's true about old capacitors. I had to replace the ones in the tach because of this. They apparently went bad while the car was not being used for 25 + years.
I also think that installing electronic ignition is the single most effective way to increase the reliability and performance of the ignition system. There are a lot of pluses when switching to electronic ignition over the original; reliability, higher voltage at the plug gap, and it is forgiving of worn parts in the distributor like a sloppy bearing clearance of the distributor shaft.... This is IMHO , your opinion may vary !
 
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