Effect of reverse battery polarity on ignition performance.

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Model T Ford Forum: Forum 2010: Effect of reverse battery polarity on ignition performance.
Top of pagePrevious messageNext messageBottom of page Link to this message  By Ernie Stepney on Sunday, June 27, 2010 - 04:34 pm:

I am still fighting with the 26 on what I consider a lack of power. The battery , and therefor the mag, (I presume) are hooked up positive ground. From past experience with conventional coil, points, condenser systems they can experience severe performance troubles if the coil is hooked up backwards. Have any of the ignition gurus played with this on a stock "T" ignition system?

"T"hanks to all in advance:
Ernie


Top of pagePrevious messageNext messageBottom of page Link to this message  By Jim Ken on Sunday, June 27, 2010 - 04:43 pm:

Ts are negative ground....As are positive I believe.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Bob Cascisa in Poulsbo, WA on Sunday, June 27, 2010 - 05:41 pm:

Ernie,

The mag puts out an AC voltage, not DC. I have seen where coil polarity will make a difference on a more modern car. It won't make a difference on a T . Does your car run on mag?


Top of pagePrevious messageNext messageBottom of page Link to this message  By Ernie Stepney on Sunday, June 27, 2010 - 06:58 pm:

The car does run on mag.. Soooo if I reverse the battery polarity and polarize the generator it should be ok just to make correct if not to run better?

"T"hanks for the help:
Ernie


Top of pagePrevious messageNext messageBottom of page Link to this message  By Norman T. Kling on Sunday, June 27, 2010 - 06:59 pm:

the coils are made to work on AC which varies according to which node the spark lever is set. It will work with battery either polarity, but the original battery polarity for a Model T is negative ground. Negative ground would work with all original equipment. It's possible however, if you are running modern equipment with transistors or diodes it might cause a problem if you reverse the polarity.
Norm


Top of pagePrevious messageNext messageBottom of page Link to this message  By John H on Sunday, June 27, 2010 - 09:39 pm:

I have seen several references to distributor type coil polarity being important so far as the spark jumps better when the hotter electrode is negative. As I recall this had something to do with cars being of positive earth as the autotransformer connection of modern coils adds the voltage created when the points open to the high tension voltage created in the secondary winding, rather than subtracting from it.

With vacuum tube theory the hotter electrode emits the electrons and is therefore negative.

An interesting question arises with magneto operation; assuming spark intensity is dependent on polarity, then what about the coil firing on the positive cycle of the AC waveform versus the negative cycle?


Top of pagePrevious messageNext messageBottom of page Link to this message  By Tom Carnegie on Sunday, June 27, 2010 - 10:27 pm:

I have studied this a bit. There are two kinds of T flywheels in regard to magnet polarity. Ones with the north seeking poles more or less in alignment with the dowel pins, and ones with the south. There are also two different polarites of coils. Some spark from the upper to lower terminal, some the other way (for any given polarity of voltage). So as Norman said, depending on which node is firing the coil (the timer is actually a mechanical rectifer when it is set on the sweet spot, and coil is "seeing" DC), what coil type you have and polarity of your flywheel, you may or may not be getting the best spark possible. The odds are about 50-50.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Arnie Johansen on Monday, July 05, 2010 - 06:14 pm:

Tom:

I thought for sure someone would have replied to your message. Perhaps everyone else understands, but I need clairification on the "seeing DC" statement. It is my understanding that the magneto puts out an AC voltage. If that is the case, I would think that the current would also reverse direction, for example if I was to put a scope on the output terminal at the hoghead.

With the timer grounding, such that the coil supplies voltage to the spark plug, I would think at any one given setting of the spark lever the polarity would be in one direction all the time(because of the fixed relationship between the piston/magneto coils and flywheel magnets). However, if one moved the spark lever to get the next place were the magneto would trip the spark plug, would not the current be in the reverse direction? In other words the coil needs a certain ampere/turns and the ignition coil does not care if the magnetic field to pull down the points is one way or the other if I got my thinking correct!

This is Arnie the guy who met you in Illinois when you made your cross country trip a number of years ago.

Arnie

P.S. Tom, was the reason you roadster in this years 500 did not come in 1st place due to a loose wire input to the coil box?


Top of pagePrevious messageNext messageBottom of page Link to this message  By Arnie Johansen on Tuesday, July 06, 2010 - 09:57 am:

Perhaps Tom is not reading this. What about some other "electrical type" charging in and explaining this.

My basis is that I have been told that electrons flow more freely from a hot body to a colder body. Therefore if the center electrode of the spark plug is negative, I am told better performance will result.

From what I read here, there is a chance you may have a negative or positive center spark plug electrode depending on your set up of the mag ring, the position of the magnets on the flywheel and the ignition coil one uses and were the spark advance lever is positioned.

When running on mag, is there any way of assuring that the spark plug center electrode is negative?

Also if running on battery, is it possible to have some plugs with the center electrode negative with other spark plugs with the center electrode positive, depending on the way the ignition coil is internally wired?


Top of pagePrevious messageNext messageBottom of page Link to this message  By Tom Carnegie on Tuesday, July 06, 2010 - 01:22 pm:

Arnie, sorry to be so slow in replying.

You said: "If that is the case, I would think that the current would also reverse direction, for example if I was to put a scope on the output terminal at the hoghead."

The voltage reverses direction, but the current only flows when the timer is making contact, so if the timer closes the circuit when the potential is at zero, the coil will only see a rising current of positive or negative, depending on which half of the cycle the timer closes.

Arnie said:"With the timer grounding, such that the coil supplies voltage to the spark plug, I would think at any one given setting of the spark lever the polarity would be in one direction all the time(because of the fixed relationship between the piston/magneto coils and flywheel magnets). However, if one moved the spark lever to get the next place were the magneto would trip the spark plug, would not the current be in the reverse direction?"

Correct, but as a practical matter nearly all driving is done on the same pulse.

Tom

p.s. Of course I remember you. I usually don't forget a guy who buys me lunch!

p.p.s In regard to the Montana 500 - let me say this. I really wanted my sister to win.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Tom Carnegie on Tuesday, July 06, 2010 - 01:32 pm:

Arnie then went on to say:"My basis is that I have been told that electrons flow more freely from a hot body to a colder body. Therefore if the center electrode of the spark plug is negative, I am told better performance will result. "

I've heard that it takes 15% more energy to make the same spark the wrong way.

Arnie said:"From what I read here, there is a chance you may have a negative or positive center spark plug electrode depending on your set up of the mag ring, the position of the magnets on the flywheel and the ignition coil one uses and were the spark advance lever is positioned. "

Correct.

Arnie asked: "When running on mag, is there any way of assuring that the spark plug center electrode is negative? "

No practical way that I can think of.

Arnie said: "Also if running on battery, is it possible to have some plugs with the center electrode negative with other spark plugs with the center electrode positive, depending on the way the ignition coil is internally wired?"

Yes, and on mag for that matter.


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