Antique Automotive Electrical Question on Battery Polarity

[BDagle]

I write articles and field questions for several Vintage automotive publications. A question has come up several times that I can not find the answer to. From the 30's into the 50's cars used either a positive or a negative grounding system. Some manufacturers used both. For instance all GM cars used negative ground, except for Cadillac and La Salle that used a positive battery ground. Ford, Chrysler, and most of the smaller companies used a positive ground. In the 50's with the switch to 12 volts, grounding was standerdized to negative. Except for Packard, the British, and some cars made in Europe. I feel that there must have been a solid engineering explination for the use of differant polarity, but I am unable to find any information on this. All I can find is a bunch of "Old Wives Tales" about corrosion, and current flow that don't hold up. I hope someone can help. Thank you! BDagle

 

[MikeHalloran]

The Citroen SM was 12 volts, positive ground.
It used an alternator that was cleverly designed so that it could be assembled for positive or negative ground.
This, I know.

Why, I don't know.


Oral tradition is a lossy communications medium.
As a result, the context within which old wives tales are true, is not always preserved.
The tales are, mostly, true.


Mike Halloran
Pembroke Pines, FL, USA

 

[MacGyverS2000]

I just read some suggested reasons why one is better than the other or why it was changed (the best was on a Cadillac site)... the posts often showed me how completely false wives tales are perpetuated by people with no engineering background.

I really liked one post about bridges using a DC current system to prevent corrosion, and if the car was negative ground all of the connections would eventually fail like the bridge. Scary...

Dan - Owner

http://www.Hi-TecDesigns.com

 

[DanEE]

Perhaps it was someone in the automotive world seeing that the telephony industry was using, and still do, positive ground in their 48 volt plant DC systems, that maybe they in the automotive world should follow same.

 

[GregLocock]

My 1964(?) TR4 was positive earth.

I think everybody finally changed to neg earth when radios became popular, as DIN sized radios only seemed to come in neg earth.



Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

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[WGJ]

I vaguely remember someone telling me that there was a change in the rate of body corrosion between neg and pos earths.
Could just be boll#cks though.

Bill

 

[MacGyverS2000]

It's bullocks... current flows in a loop, and frankly it doesn't much care which direction around that loop. Corrosion happens because of the flow (electron migration) between dissimilar metals touching each other... best you can do is add in a sacrificial metal and let it get eaten away first.

Dan - Owner

http://www.Hi-TecDesigns.com

 

[FeX32]

... many new vehicles come with a chassis "energizer". It apparently polarizes your chassis, preventing rust.
I winder whether it actually works.


Fe

 

[DanEE]

DC Power is used in conjunction with an anode system to control underwater corrosion of ships in the moth ball fleet.. reference quote below....

reference bridges... I would presume bridges or any other structure with underwater steel could make use of similar procedures to control underwater corrosion.

Vessels with military utility or logistic value are held in retention status and are in a preservation program that is designed to keep them in the same condition as when they enter the fleet. Dehumidification of the internal spaces is an effective means of controlling the corrosion of metal and the growth of mold or mildew. A cathodic protection system uses an impressed current where DC power is distributed through anodes to the exterior underwater portions of the hull, resulting in an electric field that suppresses corrosion and preserves the surface of the hull. External painting and other cosmetic-appearance work is generally deferred since it is not detrimental to the ability to activate and operate the vessel.

 

[thruthefence]

Also Gas pipelines

 

[dicer]

Maybe some confused conventional current flow, with actual current flow. In other words the true hot is the negative terminal, because the electron or actual current flow is from the Neg terminal to the positive terminal. So Positive ground makes more sense.
But since that big + sign looks better they wanted it to be the hot, no one likes negativity. LOL

 

[waross]

The telephony history may be the start of the legend.
If the central station of the original telegraph systems was positive then would the ground electrode corrosion be mostly at the remote station electrodes. A ground return would make the remote stations negative.
Whether this had anything to do with the choices for automobiles, it could be the source of the "Positive ground to prevent automobile corrosion" legend.

Bill
--------------------
"Why not the best?"
Jimmy Carter