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Old 11-08-2021, 09:36 PM   #1
rfitzpatrick
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Default Positive Ground

What's the Story why Ford went positive ground? What did the industry consider common, not just Ford Motor Company, during the Era?
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Old 11-08-2021, 10:15 PM   #2
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Default Re: Positive Ground

model T is negative ground, i don't know why he switched to positive ground.

electrons travel from negative to positive direction, maybe he thought it was the natural order of the universe.

lets hope someone has the correct answer.
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Old 11-09-2021, 09:07 AM   #3
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Default Re: Positive Ground

The advent of solid state electronics drove the change from a positive ground to a negative ground. The opportunity for the ground polarity switch arose with the change to 12V electrical systems in the mid 1950s. In development at that time was an alternator which used transistors and diodes dependent on a negative ground. By 1960 the 12V alternator design was mature enough for production, and it first appeared on the 1960 Valiant.


Original thinking was that a positive ground would minimize corrosion because it made the frame a positive anode instead of the car body. The anode corrodes and the thick metal frame was able to loose some of its thickness without consequences whereas the relatively thin body metal could not cope with corrosion.



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Old 11-09-2021, 10:22 AM   #4
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Default Re: Positive Ground

The model T didn't need much for a battery and folks didn't drive at night as much as they did with later cars that were better equipped and ran faster on the crude roads of the time. Some folks even run there Ts on 12-volts. The old 3-brush generator would have a hard time charging any battery but the starter and the coils will work on 12-volt. The magneto on the T likely put out more than 12-volts anyway.

Ford's electrical system was taxed more on the model A when they decided to use a battery type ignition. Coupled with this and a full complement of lights, they needed all the help they could get to keep the system reliable. A positive ground system follows the natural flow of electrons so it makes the system more efficient. Ford kept it this way till 1956 when they changed to 12-volt systems. 12-volt systems have twice the voltage so the efficiency level of the current flow was no longer relevant by that change. Modern designers were all using negative ground and more electrical accessories were becoming polarity sensitive so they went the normal way of the industry at the time and changed to negative ground.
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Old 11-09-2021, 10:50 AM   #5
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Default Re: Positive Ground

I worked for a while for a solar company that had very high efficiency solar panels. The systems used negative ground and the voltage built up to high values because it was more efficient for the inverters. We started having mysterious reductions in panel output. The negative charge on the frames relative to the positive charge on the cells was causing the problem. (Technically the panels were operating as a programable memory device., PROM) We switched to positive ground which solved the problem. We had to search for inverters and other equipment that could be used with positive grounds.

I don't think anyone is positive why Ford made the switch (pun intended). Best reason i heard is the anode argument.
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Old 11-09-2021, 02:57 PM   #6
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Default Re: Positive Ground

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I think Bob is right. Compare kathodic protection for shipd, steel underground gas pipes etc.
Related question ? Does the positive part of the car attract dust more ?
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Old 11-10-2021, 03:23 AM   #7
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Default Re: Positive Ground

Quote:
Originally Posted by rotorwrench View Post
<snip>


A positive ground system follows the natural flow of electrons so it makes the system more efficient. Ford kept it this way till 1956 when they changed to 12-volt systems. 12-volt systems have twice the voltage so the efficiency level of the current flow was no longer relevant by that change.

<snip>

Whooooooooot? Would you care to elaborate on that? I am a physicist and i cannot for the life of me think of any physical explanation...
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Old 11-10-2021, 08:21 AM   #8
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Default Re: Positive Ground

As an engineer, I am with Tom on this. There is no physical reason why a positive ground would be more efficient. The electrons complete a path and it does not matter which direction they are going.
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Old 11-10-2021, 12:24 PM   #9
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Default Re: Positive Ground

The current only flows one way in a DC electrical system and that is a fact. It flows from positive to negative. The ground path generally has less resistance to flow unless the cars is all crusty and rusty like many are after 90+ years. Same with the copper conductor wires but they are at the end of the circuit path in a positive ground system so the galvanic transfer of materials may have been thought to be an issue. The battery ignition was new territory for Ford in late 1927. They had used the Magneto for many years in the model T which is AC in nature but the battery, distributor, & coil was not something that Henry trusted as much until they started testing it. The thought was that the high tension spark would be more efficient with positive ground. Ford wasn't the only company to use positive ground so there was likely an industry wide consensus on this at the time. The model T had been negative ground so it was a change for Ford.

Another thing that is affected is the starter circuit in these old cars. This is the heaviest current draw in the system and also the most prone to problems in the 6-volt systems. With the body of the system already positively connected through the ground path. The flow only has to travel back to the battery when the starter switch is applied but that is where most of the deterioration would take place if that power cable was attached to the positive terminal. They felt that this would cause more arcing at the switch terminals when the starter was engaged. Maybe they were wrong but this was the early 20th century and folks had a different way of approaching things back then.
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Old 11-11-2021, 07:21 AM   #10
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Default Re: Positive Ground

Quote:
Originally Posted by rotorwrench View Post
The current only flows one way in a DC electrical system and that is a fact. It flows from positive to negative. The ground path generally has less resistance to flow unless the cars is all crusty and rusty like many are after 90+ years. Same with the copper conductor wires but they are at the end of the circuit path in a positive ground system so the galvanic transfer of materials may have been thought to be an issue.

<snip>

i think you wanna speak to those pesky electrons, they are all negative about this... ;-)


But let's agree to disagree...
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Old 11-11-2021, 08:45 AM   #11
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Default Re: Positive Ground

Conventional current positive to negative.
Electron flow negative to positive.
Go figure.
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Old 11-11-2021, 10:33 AM   #12
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Default Re: Positive Ground

Electrons were not known when electricity was first being learned about. The plus and negative was arbitrarily assigned. Later electrons were discovered and it was determined that they were negative charged.
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Old 11-11-2021, 10:43 AM   #13
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Default Re: Positive Ground

Dodge Brothers went from 12 volt negative ground to 12 volt positive ground around 1921/22 when the horn button was moved from the door, to center of the steering wheel. The reason given was, had to do with degrading contacts in the horn button.
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Old 11-11-2021, 02:51 PM   #14
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Default Re: Positive Ground

Electricity=Magic
No one REALLY knows. LOL
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Old 11-11-2021, 03:59 PM   #15
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Default Positive Ground

In Shop Manuals or engineering papers what information was provided? They doubtless had to 'splain themselves or provide justification when they completely changed from one way to the other.
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Old 11-12-2021, 11:41 AM   #16
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Default Re: Positive Ground

I was taught conventional theory but electron flow was there too but not taught in basic electricity at the time. For the purpose of calculating Ohms law it is irrelevant as to what moves where.

The other school of thought is that when a free electron moves away from its atom to another then there is a positive charge build in the proton due to the loss of the electron and that positive charge can move as a force to another proton that loses an electron.

Science is still tinkering with any way to manipulate the tiny atom to make it do what they want. There may still be other possibilities that haven't yet been discovered by science. Semi conductor technology puts things to test on a regular basis and progress will march on as new discoveries are made in the future. When I was young, I never would have thought that I'd be carrying a mini computer around as a communication device. I hated pagers when they came out because they called me out to do things I didn't want to do at all hours of the day and night. It took me a while to get used to a cell phone.
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Old 11-12-2021, 12:05 PM   #17
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Default Re: Positive Ground

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Originally Posted by redmodelt View Post
Dodge Brothers went from 12 volt negative ground to 12 volt positive ground around 1921/22 when the horn button was moved from the door, to center of the steering wheel. The reason given was, had to do with degrading contacts in the horn button.
Yes, they did. If you want to mess with someone with the current flowing from negative to positive on a DC system ask them what happens when you hook up the coil backwards. It was explained to me by someone way smarter then me that the current actually flows from the block BACK through the spark plug to the points.
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Old 11-12-2021, 01:58 PM   #18
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Default Re: Positive Ground

I had hoped I’d learn from this thread but have ended up quite confused. I have concluded with-
1. I no longer care and
2. What does it matter.
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Old 11-12-2021, 03:08 PM   #19
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Default Re: Positive Ground

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It was explained to me by someone way smarter then me that the current actually flows from the block BACK through the spark plug to the points.
Ignition coil polarity. This is a different matter and strangely enough, it has nothing to do with whether a car is positive or negative ground. The coil will work when connected either way, but the spark output at the plugs will be attenuated by about 25% if not hooked up correctly. Electrons "like" to jump from a hot surface to a cold surface, so the strike voltage required to initiate a spark is lower. There are a couple easy methods to check for correct ignition coil connections regardless of the markings on the coil itself, or whether engine is (or was) positive or negative ground.

https://mgaguru.com/mgtech/ignition/ig104.htm
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Old 11-13-2021, 12:05 PM   #20
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Default Re: Positive Ground

The spark is a product of a high voltage step up from the reversal of the magnetic field in the coil. The secondary winding in the coil is connected to the primary very near only one of the two terminals of the primary coil so it doesn't have a complete circuit to it. The polarity of the COIL depends on which side of the primary is connected to the "power" from the battery.

Back in the day, they marked coil terminals with abbreviations for "switch" and "distributor" so that folks knew how to connect them. After the change from positive ground to negative ground they started marking then + or -. This is confusing to some when using a modern coil in an old positive ground system. To further confuse things, some coil manufacturers get the markings wrong. Polarity of the coil depends on them being connected correctly to get the best spark from the other end of the secondary coil.

It takes high voltage to ionize the air enough for a spark to jump. A lot of that spark is voltage and very little is amperage or whatever you want to call it.

Electricity is a lot easier to explain if a person sticks with the conventional way of describing it.
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