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  1. #11
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    Quote Originally Posted by MrShorty View Post
    My impression is that it was done because in batteries, the outside case is often positive, which made it easier to have the case attached to the frame. It wasn't dangerous in any way, though it does appear that a positive ground system had a little more tendency to corrode the metal.
    Thanks for your answer. I don't understand what you say about the battery cases being positively charged?
    Were there any benefits to pos ground & why did they last such a short time.

    ---------- Post added at 10:07 PM ---------- Previous post was at 10:04 PM ----------

    Quote Originally Posted by mfleetwood View Post
    I thought Positive Ground was more of an optimistic state of mind, which I am sure your dad needed to have with you and your squirrel running around.
    Ha Ha Ha Ha... too funny.. Save your humor for the game threads & tell me something about the positive ground systems from the good old days Mike.
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  2. #12
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    Quote Originally Posted by stephan View Post
    Ha Ha Ha Ha... too funny.. Save your humor for the game threads & tell me something about the positive ground systems from the good old days Mike.
    Okay....Way too much typing...I am done!. I hope you are happy with this explanation.....

    Modern vehicle ignition systems use a negative ground system.

    The reason some older vehicles used a positive ground system was because their manufacturers did not realize that metal erosion caused by sparking causes the center electrodes of the engine's spark plugs to be eaten away by the sparks if that electrode is connected to the negative side of the ignition coil's high tension output.

    Such erosion can quickly make the spark-gap too large, causing late (aka "retarded") ignition problems which can seriously reduce the power output of the engine.

    So, when using a positive ground system: a) the spark plugs had to have their spark-gaps adjusted every one or two thousand miles and b) the lifetime of the plugs was only around 5,000 miles or less.

    Explanation
    It is a fact of physics that, after millions of sparks, due to metal erosion there will be less metal on the electrode that is connected to the negative side of a dc (direct current) ignition coil.

    So the center electrode of a spark plug will not erode away due to sparking if it is connected to the positive side of the ignition coil's high tension circuit and will erode away if is connected to the negative side.

    As the spark plug's outer casing is much larger in area than its center electrode, if it is connected to the negative side of the ignition coil's high tension output, the erosion of the outer casing caused by sparking is hardly noticeable and this fact has the additional benefit that the spark-gaps of the plugs hardly ever need to be adjusted during their lifetime which, nowadays, can be well over 20,000 miles.

    Up to the 1960's it used to be common to have the "+" Terminal of a truck or motor car bolted to the chassis/bodywork. That convention has been changed to the existing " -" Terminal which in Europe we call "Earth".
    To use the word "Ground" or "Earth" for a positive terminal is not really correct. Referenced to the positive rail would be more appropriate. There are also electrical circuits that are referenced to "0 Volts" in complementary amplifiers.
    Last edited by mfleetwood; 12-20-2010 at 12:23 AM.


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  3. #13
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    Thats some good stuff Mike, & true as far as spark erosion etc, but is only 1 reason why pos ground is not good. But now I'm wondering why they were negative gd. first, & then changed over to pos. ground? Was it just a sales ploy to make the buying public think they had something new & mysterious & increase sales?

  4. #14
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    Who knows.... I am thinking they were just idiots and realized there was a better way to do it.

    PS..that wasn't really me who typed that info...I stole it.

  5. #15
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    I'm hopeing there are posters here who used to work on these systems, that can tell us what the pros & cons were, why they changed to pos ground, & how many sparks they made, & fires they started with misplaced wrenches

  6. #16

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    6 volt Ford tractors [8N, 9N] in the late 40's and 50's were positive ground.

    So were Mack Trucks into the early 70's which fried alot of early CB radios...The B model Mack had (4) 6 volt batteries and a 'series/parallel switch using a 24 volt starter with a 12 volt charging and lighting system...

    The future will have us using higher voltage systems as the current 12 volt systems are maxed out
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  7. #17

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    For those that were concerned about safety, there are no more issues than exist in your negative ground system. The only thing that changes is the direction the electrons flow; otherwise it still remains a closed loop system. Electricity flows because of an imbalance created from one battery terminal (+ or surplus) to the other terminal (- or deficiency). So the difference is that instead of your common bus (the chassis) being the return line, the common bus is the supply line, and your fuses and such would be breaking the return path instead of the feed. I could see there being a potential threat if it was a high voltage system, but most of these were 6 volts, so very low threat of shock.

    It looks like the primary reason this was abandoned, besides spark plug wear, was body corrosion. The surplus electrons in the bus (chassis) attracted oxygen atoms/molecules, thus oxidizing the chassis more quickly than a negative ground system. It seems like the only reason they ever went to this was they thought electricity flowed better in that direction, but did not realize that it was cause increased oxidation, as well as the quicker spark plug electrode wear.

    In short it was just a bad idea, and they changed back.
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  8. #18
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    Good stuff Jason & Wis, thanks. But now I've thought of another ques. What would happen if you're jacking up your pos. ground car/truck on a rainy day to fix a flat tire.
    The jack is making contact with your positively charged bumper & is nicely grounded to the wet earth. Wouldn't this discharge the battery?? lol

  9. #19
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    LOL... it's all relative... plus, minus and ground are just references. Besides electrons are negative so the surplus is at anode (negative terminal) flowing toward the cathode (positive terminal). So why not say that the negative post is “Hot” and the positive is neutral.

    In a DC system it’s all about a path from the anode to the cathode. It can be all wire or part wire and part chassis or whatever. What come first the chassis or the wire doesn’t matter. Like I said it’s all relative.

    Where some are getting confused is there is no connection between chassis ground and earth ground or should I say an 'isolated' connection via tires. One could take a jumper cable from the positive post and leave it connected to a copper stake pounded in the ground and the battery wouldn't discharge one bit due to this.
    Last edited by auzivision; 12-20-2010 at 03:20 PM.
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  10. #20

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    Where some are getting confused is there is no connection between chassis ground and earth ground or should I say an 'isolated' connection via tires. One could take a jumper cable from the positive post and leave it connected to a copper stake pounded in the ground and the battery wouldn't discharge one bit due to this.
    This kinda hits it. Even just by jacking up the car, you're not going to lose much if any charge, even on a positive ground system. The reason being is you are not completing the circuit. When a battery is "charged", it is just at an imbalance between poles. "Discharging" a battery basically means allowing current to flow from the anode to the cathode and returning the battery to a balanced state (no excess of electrons at either post). So if you're only touching one pole, even connecting it to earth ground, you're not creating a full circuit. both poles would have to connect to earth ground to create a circuit.


    Many people confuse DC with AC when it comes to "grounding". With AC systems (home electric), electrons are actually pushed, then pulled, then pushed in a repeating cycle, using Earth as a common ground to push electrons into and pull electrons from. so, if you touch the positive feed in your house while being grounded well (standing in a puddle, etc), you will get shocked. If you can take the shock for a short time, you can actually feel the "pulses" of the push/pull cycle. You're completing the circuit, because earth ground is part of the circuit.

    In a closed loop system, such as Car DC system, earth ground is not part of the circuit, so it is irrelevant on current flow.

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