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Old 07-30-2010, 06:32 PM
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Why Neg. Ground vs. Pos. Ground?

We were having a discussion today at work about positive ground vs. negative ground electrical systems in cars. Everybody there had a good understanding of auto electrics, but nobody could say definitively why negative ground was better. I wonder if some of you here could shed some light on this subject for us.

For the most part, American car manufacturers used positive ground electrical systems in the 6 volt days (except for GM, REO, Ford Model T's, some Lincolns and pre-GM Cadillacs) until they switched to 12v around 1955, then they all (except for Packard) switched to Negative ground electrical systems.

The question is why. What is the advantage of negative ground electrical systems over positive ground systems?

I know that some of you on this site have a background in electrical engineering, and many of you have forgotten more than I'll ever know about electricity, So I ask you to please tell us - What are the advantages to having a negative ground electrical system in a car versus positive ground?

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Old 07-30-2010, 07:46 PM
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I know little about electrical, but I think there is no advantage one way or the other.....Its just the standard way of doing it for most. Just like why do we drive on the right side of the road and those silly British drive on the left?
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Old 07-30-2010, 07:56 PM
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You really don,t want to open this can of worms.
Not an engineer,but schooled and still have not found the answer.
What we have here are 2 theories about current (electron) flow.


Conventional theory. Which I bekieve accounts for positive ground cars.

Electrons flow negatrive to positive outside the battery.

Electron theory is as we have become accustomed to is where electrons flow positive to negative outside the battery.

This makes sense to me as the plates in the battery will lose mass from the negative plate and is deposited on the positive plate as electrons move from the negative(grounded post ) to the positive post INSIDE the battery.

I assime that at some point reserch and development deternmined that we would all be better off if we followed the electron thoery so everyone changed.

The electrons really don't care as long as all the electrical equipment is on the same page.

This may not answer your question.
Maybe we can get an electrcal engineer to post a simpler answer. Bob
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Old 07-30-2010, 10:56 PM
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Quote:
You really don,t want to open this can of worms.
Not an engineer,but schooled and still have not found the answer.
What we have here are 2 theories about current (electron) flow.


Conventional theory. Which I bekieve accounts for positive ground cars.

Electrons flow negatrive to positive outside the battery.

Electron theory is as we have become accustomed to is where electrons flow positive to negative outside the battery.

This makes sense to me as the plates in the battery will lose mass from the negative plate and is deposited on the positive plate as electrons move from the negative(grounded post ) to the positive post INSIDE the battery.

I assime that at some point reserch and development deternmined that we would all be better off if we followed the electron thoery so everyone changed.

The electrons really don't care as long as all the electrical equipment is on the same page.

This may not answer your question.
Maybe we can get an electrcal engineer to post a simpler answer. Bob
Very close Bob
You do have a few things mixed up. Yes electrons move from negative to positive. This is not a theory it is a known fact. It is also known that opposites attract. To get a better understanding of why a negative ground system was chosen we need to look at the molecular level.

In an atom there are three parts:neutron,proton, and electron. The electron orbits the nucleus(protons and neutrons). The property or willingness of an atom to give their electrons ultimately determines the materials conductivity(way more to it than that; this is a simple description). By natural law materials are or tend to stabilize in an equal state(once again there are exceptions and I'm just generalizing). We know that an atom has an equal number of protons and electrons. Therefore an atom doesn't have a charge. Another important property we need to know about atoms is that they can gain or lose electrons and stay the same chemical makeup(ie copper is copper even when it is an ion) When an atom gives or gains an electron it becomes an ion and can be considered to have a charge.(This is important). The movement of these electrons is what creates a charge or difference/potential. The movement of these electrons is electricity! If the electrons flow in a uniform direction we have a current. That is a lay description of what electricity is.

Oops, I forgot to mention that an atom doesn't give up protons. When you figure out how to do this let me know. I've got a lot of lead that needs changed into gold

Anyways, back to electricity. Since we have addressed the molecular level lets get some vernacular out of the way. Voltage is the potential of electron flow. When you have a battery sitting on a shelf not in a circuit it is said to have 12 volts. Think of this statement as there is a difference of electrons equal to 12 volts. Or there is a potential of electrons to flow from the negative side to the positive side(greater the potential the greater the voltage). This is important when you try to justify a 1 foot section of wiring during a voltage drop test. When we perform a voltage drop we measure a voltage. If there is a resistance we will see a voltage(for example maybe 1 or 2 volts). But wait! How can a piece of wire create a voltage?!! Only batteries or generators and stuff can do that right? Wrong! Voltage is not something we create it is a measurement of potential Now, the easiest property of electricity to define is current(in lay terms). Current is the amount of electrons flowing(quantity).

Also, it is important to understand how a battery works. The chemical reaction of the lead plates(calcium, antimony, and lead) and sulfuric acid creates a solution of ions. These ions donate their electrons and that is where the original electricity starts. Without the chemical process there would be no potential flow of electrons(voltage). It is not just electrons flowing from a negative plate to a positive plate. It is the gaining and losing of electrons of the plate. When a battery discharges the chemical process sulfates the plates(plates lose electrons). When a battery is charged the chemical process is the reverse and oxides the plates(electrons are gained).

Ok who is lost?
Alright so you are asking yourself what does this have to do with negative and positive ground systems. Quite simply it is a matter of effort. Every conductor in that vehicle that connects to ground essential becomes eligible to give up electrons.There is a potential huge imbalance of negative ions. Another way to comprehend what I am saying is to think of a negative ground system as allowing a chassis to be an amplifier. This is also the bane of negative ground systems! In a positive system the positive side will receive the electrons. Therefore only the negative feed wires will be donating the electrons on the current side of the load. This requires larger wires when a large amperage is required(this is true in ground systems but Im referring more to the momentary jumps like ignition coils and injectors). Therefore a positive system in essence will require better quality components. So, from a manufacturers stand point it is a lot cheaper to go negative. Also, standardizing the system played an important role in the decision. When computers came along it pretty much sealed the deal for negative ground systems in autos.

Ultimately it comes down to the fact that: negative ground immitates natural electrical flow, the industry needed a standard, and it can be cheaper for manufacturers. There is way more theory behind it, but I'm tired and want to go sleep.
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Old 07-30-2010, 11:15 PM
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Cape Cod Bob is correct, let us remember that the negative electrons travel on the surface of the conducter, therefore the exclusive use of stranded wire for DC applications is necessary for flow. never use solid wire on your vehicle. Just thought I'd throw that in.......cause I'm taking a break from rewiring a guys hotrod that was wired with 12/2 ROMEX a contractor left behind when he rewired the guys house.
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Old 07-31-2010, 12:10 AM
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Not sure if this is true or not, but I was told because the positive terminal is usually the one that corrodes, there was concern that using it as a ground would cause corrosion problems on the frames of vehicles. Again, not sure this is accurate just what somebody told me once.
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Old 08-01-2010, 09:41 PM
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Thanks for all the responses. I really appreciate the effort you guys put into your replies.

It all makes perfect sense now.
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Old 08-01-2010, 09:55 PM
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Like my boss told me when I got picked for the **** job "eenie meenie minnie moe......"
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Old 08-02-2010, 06:17 AM
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Ethn_Bert, that was one of the most concise explanations I've read in a long time. Could you go one step further and offer an explanation of how electron flow is accomplished in a circuit with just a generator, ie no chemical process such as a battery.

Are there any references you can point to on the web, that are as lucid as your explanation above, that go further into the theories and other facts regarding electron flow, charge, potential, etc? I'd like to get into it a little deeper.
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Old 08-02-2010, 07:15 AM
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I'm not sure I grasp Ethn-bert's explanation as to why one system is better than the other. As far as I know, for any electrical circuit to operate, the electron flow is constant around the circuit loop. The same current flows in the positive battery cable as in the negative one. I would say that conventional current theory is the only reason for a negative ground system, although as I said....I didn't quite follow E-Bs theory 100%.

Conventional circuit flow (positive to negative....the opposite of electron flow) is used in all electronic designs. In order to (easily) use these designs, such as radios, ignition computers, etc., a negative grounded battery system is required. It could very well be that the change from positive grounding to negative grounding occurred about the same time period as solid-state electronics (such as radios) started making their way into automobiles....maybe the mid to late 1950s?

On the other hand, the only positive ground systems I've seen were 1940ish systems which used a 6 volt battery. Like my Model M John Deere tractor. These could be easly converted to negative ground by swapping the connections on the igntion coil and re-polarizing the generator. The starter motor always seemed to rotate the correct direction regardless of polarity. And for a short period of time 6 volt negative ground systems were used, such as on my 1954 Chev truck....or was in a 1952.....can't remember now.

Another thought may be errosion of the brushes/commutator in generators. Do you want the brushes to give up material, or the copper commutator? Which would make the generator last longer?

So wether E-Bs theory is spot on or not, there may be other reasons to have made the change to negative grounds....convention standards, generator longevity and the introduction of solid-state electronics.

I did find this on Wikipedia:

In modern automobiles, the grounding is provided by connecting the body of the car to the negative electrode of the battery, a system called 'negative ground'. In the past some cars had 'positive ground'. Such vehicles were found to suffer worse body corrosion and, sometimes, blocked radiators due to deposition of metal sludge.

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Old 08-02-2010, 04:28 PM
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I'm not sure I grasp Ethn-bert's explanation as to why one system is better than the other. As far as I know, for any electrical circuit to operate, the electron flow is constant around the circuit loop. The same current flows in the positive battery cable as in the negative one. I would say that conventional current theory is the only reason for a negative ground system, although as I said....I didn't quite follow E-Bs theory 100%.
I was only referring to the direction of flow. Yes the electrons flow on the positive battery cable, but they flow in the opposite direction of conventional thought.
Conventional theory has nothing to do with the negative ground. From an engineering stand point in an abstract theoretical world positive and negative ground systems are equal. However, multiple other physical and chemical properties affect electrical systems.

Quote:
Conventional circuit flow (positive to negative....the opposite of electron flow) is used in all electronic designs.
I believe you are confusing current path wiring diagrams purpose and equating them with conventional theory. Current path wiring diagrams are used in engineering to simplify electrical circuits. The ground is at the bottom of the page and the Load is at the top.
Further, a wiring diagram doesn't show electron flow at all. The viewer of the diagram interprets the diagram as flowing from the greater(+) to the minor(-) which is opposite of the actual physical flow(minor to greater). Take a look at a wiring diagram and look at the whole picture. It is very hard to remove one's self from the interpretation of a diagram. We are taught from a very small age that electricity flows greater to minor(conventional theory). Conventional theory is taught in grade school because it is much too difficult to explain electron flow without an understanding of more than basic chemistry. Since conventional theory(greater to minor) correctly teaches most of the basic electrical principles it has been chosen as the basic foundation of education in respect to electricity. Electron flow is taught in chemistry in higher education and high school. Education is a process. Sometimes you have to learn a very basic understanding before the contradictory understanding and ultimate theory. I hope that makes sense

Quote:
Another thought may be errosion of the brushes/commutator in generators. Do you want the brushes to give up material, or the copper commutator? Which would make the generator last longer?
Don't confuse the donation of an electron with the physical property of material wear. I cannot tell you whether or not if the the brushes wear faster on a negative ground systerm compared to a positive ground system. However, brushes wearing are a physical property not an electrical property.

Quote:
Like my Model M John Deere tractor. These could be easly converted to negative ground by swapping the connections on the igntion coil and re-polarizing the generator. The starter motor always seemed to rotate the correct direction regardless of polarity.
Argess, this statement is a perfect segway to answer cucumbers question. I will explain why the starter turns the same direction and what exactly is happening when you polarize the generator. and answer cucumbers questions However, I cannot do it at this time. I'm on vacation and it is time for me to cook the fresh swordfish. I'm gonna stuff myself!
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Old 08-02-2010, 05:46 PM
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There are laws and there are theories,enter the electron "THEORY"

VIVA TESLA!!!!!!
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Old 08-02-2010, 05:59 PM
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Very good explanations.

If you want reading the theory, all you have to do is look up battery theory(DC theory). Or you can go to any Radio Shack and get a basic circuit book and it will go over the basics.
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Old 08-02-2010, 06:17 PM
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Turns out the OPs question isn't so new. Here's a link where the same question is discussed...in fact remarkably similar to this thread, except no mention of a swordfish dinner. There seems to be some thought about corrosion being a factor, although there are opposing views on which ground polarity seems better when it comes to corrosion.

http://www.jalopyjournal.com/forum/s...7935&showall=1

I still think it's all about convention and getting a simple thing like a car battery reversed waas easier then changing the rest of the world's convention on electrical design and current flow.

I'd probably try to forget about electron flow. Unless you are designing some sort of particle beam apparatus, like a Klystron, electron flow isn't a concern. I always liked the old analogy of a pepsi bottle (even though the analogy is incorrect, it gets the point across): Looking at a bottle of pepsi, is it the bubbles going up, or the liquid flowing down?
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Old 08-02-2010, 08:42 PM
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Originally Posted by cucumber1949
Ethn_Bert, that was one of the most concise explanations I've read in a long time. Could you go one step further and offer an explanation of how electron flow is accomplished in a circuit with just a generator, ie no chemical process such as a battery.

Are there any references you can point to on the web, that are as lucid as your explanation above, that go further into the theories and other facts regarding electron flow, charge, potential, etc? I'd like to get into it a little deeper.
Simple answer Provide electricty to a motor and get motion
provide motion and get electricity
How we get electricty from a DC generator is the reverse of a DC motor, We prvide motion by turning the shaft of the generator. Also refered to as a rotor. Within this rotor are windings and we a call that the armature.The windings are seperate from each other and connected to opposing commutator segments that are on the end of the rotor. This is where the brushes rest.
We have to provide electromagetic force in the form of permenent magnet around the rotor or with windings of wire referred to as fields . When we apply a voltage to these wfiekds a electromagnetic force is applied.
This force will cause current to flow in the armature as it turns through this force just like in a transformer where we get electricity out when we apply electricty in and there is NO actual connection.
So that is how we get a generator.

Tesler was way ahead of his time.
There have to be tons of books out on all this I would try at the library first.
Like I said, can of worms LOLLOLLOL
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