6v positive ground question

[Merle Coggins]

Always Pos-Pos and Neg-Neg no matter what. Just don't let the vehicles tough each other.

[navyboy]

I believe one of the big reasons why car makers made the switch was people kept getting confused on the matter so they made it easier on the consumer. I have heard other sreasons as well. It also surely became cheaper to wire the car needing smaller guage so material cost came down in that aspect. My understanding with positive ground is that it was thought that current flowed more effiecient in such manner but truth me told it flows the same if I remember correctly, someone will surely chime in and educate me and others more.

[TodFitch]

I believe one of the big reasons why car makers made the switch was people kept getting confused on the matter so they made it easier on the consumer. I have heard other sreasons as well. It also surely became cheaper to wire the car needing smaller guage so material cost came down in that aspect. My understanding with positive ground is that it was thought that current flowed more effiecient in such manner but truth me told it flows the same if I remember correctly, someone will surely chime in and educate me and others more.

12v allows for smaller diameter (larger gauge number) wire for the same power output. So you can save on copper. Weight may have been a consideration but I'm guessing it was more about cost and keeping the size of the wiring bundles smaller as more and more electrical gadgets were added to cars. There was a push a little while ago to get the auto industry to switch to 48v for similar reasons to the switch to 12v but that seems to have been dropped.

 

Story I heard about all going to negative ground had to do with the advent of solid state devices (radios and later voltage regulators) that were in development and that the early semiconductors were easier to make if you had a negative ground.

[busycoupe]

I tried looking this up on the web and found a variety of opinions.  One that sounded plausible was that he polarity could have something to do with the erosion of the center terminal on a spark plug.  However, I suspect that Tod is correct about trying to make the cars compatible with semiconductor electronics.  As an interesting aside, I wanted to put a modern Sony 12V neg. ground radio into my '48 Dodge with pos. ground.  To do this, I bought a 6V pos ground to 12V neg ground converter.  When it arrived I was surprised and confused that the instructions said to ground my new radio and the converter to the chassis of my car.  I was so convinced that this had to be incorrect that I called the company that sold me the converter.  They told ,me that the converter works by stepping up the 6V + charge to 18V +.  This is connected to the input on the radio.  The radio "sees" a 12V neg drop from the 18V input to the 6V chassis!  It sounds crazy until you realize that the flow of electrons is determined by a relative difference in potential.  Anyways, everything in my car, except the new radio, is 6V pos. ground.

[Plymouthy Adams]

I have seen this so  many time in electronics...freak your chicken the first time you come across it...

[jeffsunzeri]

You know for sure that the move to 12 volt systems from 6 volt were for either weight savings (as in aircraft applications going from 12 volt to 24 volt) or cost savings. Back in the '50s weight was not much of an issue for Detroit, so you can bet the move to 12 volt was cost savings.

 

The British automotive industry didn't change to negative ground for many years after going to 12 volt systems, so they at least found an advantage to staying with a positive ground (earth) system.

 

A clue to which is "better" can be seen with your DC welder. Look at the change in behaviour from welding with the electrode negative vesus the electrode being positive.

The final decision (English went one way, Americans another) is based on what metal transfer behavior you were most comfortable with.

 

In practice, at least in my somewhat extensive experience with both systems, both work just fine in the real world as long as you don't mess too much with the way the factory did it.

[Ulu]

Oh crap. It's been nearly 20 years since I used a stick welderlast.  I forget which way it goes.

 

Frankly, I don't think I once bothered to touch the polarity switch on any welder I've ever used.

 

Clue me in Jeff!

[Don Coatney]

Polarity makes no difference on my welder.

 

[jeffsunzeri]

For an AC welder, polarity changes at 60 HZ (cycles per second). Most of the common stick welders in the small shop/garage/home are AC welders. Ergo, you don't get to select ground polarity.

Industrial, commercial stick welding is done with DC generators, as is all ferrous welding via TIG (heli-arc).

Generally, using a DC welder with the stick or electrode positive (DC reverse) and the work negative (grounded) results in deep penetration of the grounded material.

Using DC with the electrode negative and the work positive (DC straight) results in fast and difficult to control electrode consumption.

Some good general information on this is available from here: http://www.lincolnelectric.com/en-us/support/process-and-theory/pages/understanding-polarity-detail.aspx

Your MIG welder requires electrode positive (DC reverse) polarity for almost all operations.

Given all this, an electrical engineer considering DC circuit design might ponder whether he or she would prefer to have the frame or the connector erode quicker in the event of a corroding connection, or in the performance of various electrical components (like spark plugs).

Ultimately in a circuit that is as robustly built as an automotive system, it doesn't really matter too much, as evidenced by the fact that Roll Royce 12 volt positive ground electrical systems are no worse than say an Imperial's with 12 volt negative ground.

Edited April 21, 2014 by jeffsunzeri

[Don Coatney]

Reason I posted the picture of my welder is because it is AC only and as I said polarity is not changeable. Most important thing when using an AC welder is to use AC electrodes made specifically for AC welding.

[jeffsunzeri]

This is from a 1978 Rolls Royce manual:

"...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"

[Ulu]

This is from a 1978 Rolls Royce manual:

"...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"

So I was right about the electrolysis?  I've never had a radiator ground strap though now I'll remember it, since I intend to have a rubber mounted radiator.

[Dana]

Does a starter know the difference between positive and negative ground?

[martybose]

1 hour ago, Dana said:

Does a starter know the difference between positive and negative ground?

No it doesn't.  I was pleasantly surprised when I changed my car from positive to negative ground that the starter was unaffected.

Marty

[Plymouthy Adams]

1 hour ago, Dana said:

Does a starter know the difference between positive and negative ground?

non permanent magnet...you would have to change the polarity of the brushes to affect rotation

[DrDoctor]

Afuente,

   Our car was 6v neg ground when we got it several years ago. Since then, I’ve completely rewired it using a Ron Francis harness, and have had absolutely NO problems with it—and YES, it’s still 6v neg ground. I didn’t change it to pos ground as I was told I’d have to replace the starter, and the generator. But, since they both were working just fine, I didn’t see the need to waste money just to switch polarity. There may have been cheaper alternatives to accomplish the polarity-change issue, and it may not have even been necessary, but quite frankly, I just simply didn’t want to bother with it.

[TodFitch]

2 hours ago, DrDoctor said:

Afuente,

   Our car was 6v neg ground when we got it several years ago. Since then, I’ve completely rewired it using a Ron Francis harness, and have had absolutely NO problems with it—and YES, it’s still 6v neg ground. I didn’t change it to pos ground as I was told I’d have to replace the starter, and the generator. But, since they both were working just fine, I didn’t see the need to waste money just to switch polarity. There may have been cheaper alternatives to accomplish the polarity-change issue, and it may not have even been necessary, but quite frankly, I just simply didn’t want to bother with it.

I believe you were told wrong: Neither the starter nor the generator need to be replaced. The starter should "just work". The generator would have to have the magnetic field in its soft iron core reversed which can be accomplished by "flashing" it, at task normally accomplished by momentarily shorting a couple of terminals on the voltage regulator.

Longest part of the job of changing polarity, as long as you haven't added components/accessories using solid state electronics, is probably swapping the battery cables.

The reason why it is so easy is that the starter motor and generator use field coils rather than permanent magnets. In the case of the starter when you reverse the polarity on it you are reversing both the field and the armature so the direction of rotation remains the same. Similar concept on the generator.

Edit: You may also have to swap leads on the coil. So I guess that adds a little time to the conversion.

[Los_Control]

On 4/17/2014 at 6:28 PM, Ulu said:

According to my 1957 Motor's manual, negative ground is now used because it generally gives a hotter spark.

Careful there, if you let that info out to to many people, everyone is going to want a pos ground flathead mopar!

[DrDoctor]

Todd,

   You’re probably right about the starter, and the generator. I debated on this, but I just didn’t want to go thru the hassle of having to polarize the generator and/or the starter (because I wasn’t sure it was even necessary). I admit to taking the easy route on this—since the car’s a driver (it looks really good, but it’s not a show car), and since it functioned just fine with the negative ground, I left it that way. To be honest—if the insulation wasn’t literally falling off of the wiring, I probably wouldn’t have rewired it. But, since it was, I elected to add circuits rather than just have the one fuse in the headlite switch. And, while I was at it, I added turn signals into the park lights, and the tail lights, and made the tail lights illuminate along with the trunk light when the brakes are applied. I killed a lot of problems with the same rock on that one. As for the coil, I connected it as per a 12v negative ground system. Thx.

[DrDoctor]

   

Edited October 27, 2017 by DrDoctor

[martybose]

I think the issue with the radio only applies if you have changed to an electronic oscillator; when I switched from positive to negative ground with the original radio it kept working just fine.

Marty

[keithb7]

Speaking about auto makers going to 12V:

12V turns a starter faster it seems. I've been told a 6 Volt V8 engine, will quickly kill a 6V battery if it doesn't start quickly. 

By the mid-50's higher horsepower V8 engines were becoming more popular. Overhead cams. Higher compression engines. Larger displacement. These engines needed to spin faster to fire up. The 12V system was an answer to these problems. 

Is this right?

[Plymouthy Adams]

12 volt is smaller in design and less wire and lighter weight  less amperage...the same will drive the 24 volt trend as it did in aircraft years ago.  the straight 8's in 6 volt would require 410 amps whereas the 6 was but 335 and the first 12 volt Chrysler starter in 1955 drew 212

[DrDoctor]

    

Edited October 27, 2017 by DrDoctor

[Labrauer]

So after reading all the post on this topic I am still confused to what needs to be done to go from positive ground to negative ground. I just got a new wiring harness for my 48 Plymouth and before I hook any wires up I would like to change to 12 volt negative ground. I know there are lights, and a few other things that need to be changed over to 12 volts but this electronic stuff is not my thing. Is there anybody out there that can explain the procedure of changing 6 volt to 12 volt and list the parts that need to be changed in plain old english. Like what do you mean when you say "change the polarity" in something and ect.