+6 or 12-?

[Joe Johnston]

Reading the above post in the 64-66 section about the Amp guage got me thinking (always dangerous for me).

Why did American cars switch to a neg ground when they became 12V? Most 6V vehicles are + ground and most 12 are - as we know, but not ALL 6 or 12V vehicles around the world were this way - so it isn't a mandatory thing. Standardization is good, but why the change to a negative ground when the systems will work as positive ground if originally built that way?

[simplyconnected]

Joe, I think the need for standardization came when the big three started buying accessories from all the vendors. Think about it, Ford never made power antennas or power mirrors, etc. They could control the wiring on seats and windows but it gets too much when you think of convertible/retractable top power sources (another vendor item), radios, alternators and electronic voltage regulators, etc. Then, there are external devices that attach to the car's ground like trailer brakes.

Any departure from 12-v neg gnd is a pain. My cousin's Amphicar (built in Germany 1965) has 12-v pos gnd. What a pain finding a decent radio. GPS is popular (especially in the water). Forget about charging any accessory from the lighter.

[Joe Johnston]

Interesting thoughts. Since a DC system will work equally well either way with their matching accessories, I was hoping there was an electrical theory someone would know as to why the change. Just going from 6v to 12v isn't it because your example of the Amphicar (and others) proves that 12V pos ground is just fine - just don't mix just like not mixing 6V into a 12V system. I'm sure we would have chaos if GM did one way, Ford the other, and so on. I realize it had to be one or the other but with such a long history of + ground, all of a sudden we went to - with 12V? I'll try and see what I can learn and also which way the 8V and 24V systems were.

[Jimz Bird]

Inquiring minds want to know -

"Theoretically they (Positive Ground) accelerate corrosion and clog up radiators. This from Rolls Royce, explaining their decision to switch (back) to negative earth:

Quote:
'...it has been found that cars wired positive earth tend to suffer from chassis and body corrosion more readily than those wired negative earth. The reason is perfectly simple, since metallic corrosion is an electrolytic process where the anode or positive electrode corrodes sacrificially to the cathode. The phenomenon is made use of in the "Cathodic Protection" of steel-hulled ships and underground pipelines where a less 'noble' or more electro-negative metal such as magnesium or aluminium is allowed to corrode sacrificially to the steel thus inhibiting its corrosion. Also the radiators of post war cars wired positive earth have a tendency to become blocked due to electrolytic deposition of metallic salts, particularly in hard water areas. For this reason it is important to bond these radiators to the chassis and bodywork with flexible copper braiding so that they are at 'earth' potential.'"

More:
"There is no strict answer as to 'why' American cars are negative ground based systems. Rumors are that it was because of Benjamin Franklin's guess to the 'poles' of electricity as to which way current actually flowed, and degenerate into derogatory comments about American's ignoring the laws of physics. The convention for labeling batteries, despite physics, remains however.
Despite any claim to the contrary DC Current ALWAYS travels from the ground (-) side of a battery to the positive (+) side; because electricity is made up of free electrons that accumulate on that side of the plate as a result of a chemical reaction.
Also, all switches (except immersed switches - no arc switches used for explosive gas environments) will 'arc' when the contact is almost made.
Also, production prices between positive and negative chassis systems are no different as electrical systems are the same in concept as well as production. There is no "requirement" that one system have a master switch (or any switch for that matter) because of its ground source. It is true however that most of these positive systems use better wiring, and relays for current load where American cars rely on the switch itself to handle the current load; which increases the cost and complexity of the system (Lucas prince of darkness, Jaguar comes to mind).
Lastly, Negative Ground based chassis systems have one inherent problem not normally seen on a Positive chassis system; known as a ground loop. A "ground Loop" is properly stated as an electron potential imbalance; where there are more electron's available in one point of the car as opposed to another point in the car / this is eliminated in positive based systems and compensated for in negative systems by running ground straps through the chassis."

Last point is why Dave et al. say to put more "grounds" around the car. - I think.

AND if you want to read an interesting thread:

http://www.hotrodders.com/forum/why-neg-ground-vs-pos-ground-181903.html

[Joe Johnston]

Thanks for the links!! Good reading and LOTS to digest. Wish I were an electrical engineer to be able to understand it all - will have to re-read that link.

Here is what I gathered from the reading:

1) increased corrosion resistance
2) negative ground immitates natural electrical flow
3) the industry needed a standard
4) it can be cheaper for manufacturers

I should have known the "bean counters" would have been involved in this somehow!

[Jimz Bird]

One other thing I read was that it was easier to do "noise suppression" of static on a negative ground.

How did we ever keep these running when we were kids without knowing all this stuff?
I had to check out the "Motor's Auto Repair Manual" from the library. Seems like the Ford section was pretty greasy.

With the Internet, nice but - Sometimes TMI

[simplyconnected]

Gentlemen, we can argue which direction electrons flow, or which is better for galvanic reaction but NONE of it matters.

Cars don't have hulls immersed in salt water, they are electrically isolated from the road by four rubber tires and a lot of air space. So each car has its own separate electrical system.

We do NOT bond our radiators because:

1. It isn't necessary,
2. New radiators have PLASTIC tanks,
3. Radiators are not current carrying conductors.

All these arguments could be moot issues, if the manufacturers used BOTH wires, like all our household appliances. (I know, but Edison's first power was DC.) Despite any claim to the contrary, opposite magnetic poles attract and so do opposite electrical polarities.

ALL modern car bulb sockets include their own ground wire because light housings are plastic. Oh, and modern car electric window motors have only two wires, neither of which are grounded (because they switch both wires for direction change).

So, if car radios came with two wires, the radio could have an internal bridge rectifier and it wouldn't matter which wire connects to ground. - Dave

[Jimz Bird]

Gentlemen, we can argue which direction electrons flow, or which is better for galvanic reaction but NONE of it matters.

Soooo, to sum up - Good, clean, multiple ground connections.

[simplyconnected]

It's impossible to have too good of a ground. I tap off my main copper ground wire just for the dash. It's all about good low-resistance connections. Brass screws, flat washers and nuts work very well, and they don't rust. Stainless isn't as good because it contains nickel (higher resistance).

We have seen cars on the road where one headlight is dim, or a tail light that switches back and forth when the brakes turn on. Bad grounds are the cause.