battery question

[Anonymous-0]

I was wondering why were are the older farmalls 6 volt positive ground?

 

[paul]

Pretty much all old vehicles - cars & trucks too - were 6v positive ground.

When diesel engines came out, not enough cranking power (and brighter lights, and....), so they switched to 12v. They also learned more about electricity, & realized negative ground was a better way to go.

It's probably more complicated than that, but pretty close to how it went.

--->Paul

 

[Anonymous-0]

Half the cars and trucks built in 1940 were positve ground.All 6v tractors Ive worked on were positive ground.There are some 12v positive ground systems in use.

 

[Cummins 1955]

They went to negative groung with the beginning of electronics. Alternators like negative ground better, probably cheaper to manufacture.

 

[Dieselrider]

When electric starters first came along that is all the manufacturer was trying to use electrically. There wasn't need for more voltage at the time. Then they added lights and more gauges and other electrical requirements. Just the same way houses used to be wired with old knob and tube wiring as the only electric needs were a few light bulbs.

There is talk that cars (with all the electric needs from all the "gadgets" of today) going to a 24 or 36 volt system someday. Too much draw for the 12 volt system to keep up.

 

[buickanddeere]

It has to be either negative or positive chassis return. 50/50 chance of being + or -.
Double the voltage and you can carry the same power with less losses with 1/2 the current.
Ground is AC not DC. As this is when a ground rod is driven into earth to bond electrical service neutrals to.

 

[Kentb of SWMO]

Allis-Chalmers used positive ground on even their 12 volt systems until they started using alternators. There is one over the road truck builder who the last I knew STILL uses positive ground. Mack I think. big truck alternators DO NOT connect the negative side of the diode pask to the case. It is connected to a NEGATIVE post. This way the alternator can be used with both a Negative Ground system or a Positive Ground system. As said most electronics like negative grounds because the NPN junction transistor is more common, But transistors with a PNP junction are sais to switch faster.

Kent

 

[Phil Doolittle]

In Positive Ground Direct Current ( DC ) systems Regardless of voltage spark ignition systems in internal combustion engines the spark starts from the outer metal electrode, not the center electrode. The electrical erossion due to the spark eats away the steel. This is the part you adjust for the spark gap. When early spark plugs were made you could disassemble them to clean the center electrode and file it FLAT. This aided the intensity of the spark hence ignition. Further improvements in sparking plugs were to seal the porcelin to the center steel rod as well as to the threaded base. As newer harder alloys were developed the internal rod is connected to harder metals such as platinum. Certain metals carry electrical current better(lower resistence). Copper is better a conductor then steel,but is too soft and melts at a lower temp. then steel as an example. SO, the center TIP only is now the harder better conductor in preminum plugs. AND yes this allows the Polarity of the NEGATIVE ground system to start sparking at the center electrode to the outer carbon steel body. BE SURE YOU FOLLOW THE POLARITY ON THE SPARK COIL IN THE CIRCUIT: ALSO helps the intensity of the Spark. Check the 50 TIPS on this site for FORD "N" tractors for further explaination. These early discoveries were by Edison & his good friend Henry Ford.

 

[KEB1]

I'm an electrical engineer with 30+ years experience, and I have never been able to find a definitive answer to the positive/negative ground question. Technically, the term "ground" is a misnomer; there is no connection to physical earth. However, in common usage, an electrical reference point such as a tractor or car chassis is commonly referred to as "ground".

Contrary to what Phil says below, the polarity of the high voltage spark has nothing to do with whether the positive or negative side of the battery is connected to the reference point. The polarity of the high voltage spark is determined by the relationship of the primary and secondary windings in the coil. In fact, the high voltage pulse is always negative with respect to the reference point, i.e., "positive ground". That's why the primary connectors on ignition coils are marked '+' and '-'.

The center electrode on a spark plug is always hotter than the ground electrode. Just like the hot filament in a vacuum tube, the hotter surface emits electrons easier. Therefore, by having the center electrode negative, it is easier to initiate a spark from the hotter surface.

I've heard a number of opinions for the positive/negative ground debate in old vehicles, including electrolytic effects on chassis corrosion, but have never found a defnitive engineering reason for one or the other.

Until electroncis started appearing in cars it really didn't make any difference as near as I can tell. Lights, starter motors, etc., don't care which direction the electrons move, only that current is flowing. When electronics started to become common, there was a marketing reason for standardizing so that manufacturers didn't have to build both six and 12 volt and positive and negative ground hardware.

The major reason for going to higher voltages is based on on the necessary wire size, which is driven by current. For example, to light a 50 watt headlamp takes about 8 amps at six volts, 4 amps at 12 volts, and 2 amps at 24 volts. Higher voltage = lower current flow for a given load = smaller wire size. Lower current also equals less losses for a given wire size, making higher voltage systems more efficient.

If I ever find a defnitive explanation for why one polarity was used over another, I'll post it. I suspect it was just convention, i.e., one manufacturer started out with a particular voltage/polarity, and others followed suit.

If any out there knows of a definitive refernce, I'd love to see it. I have a book from the 1920's which describes automotive electrical system operation, and it is silent on the issue of polarity.

Keith

 

[Coloken]

Well said Keith. Does not realy matter except in vacume tubes and electrolytic action. Maybe in curret rail in railroads. I remember when transisters came in and they had to invent "holes" cause it was backwards and they though only electrons moved. The English in electronics refer to "ground" as chassis ground and "earth" as the earth ground. I think that its way around!

 

[Bob]

GREAT post, Keith!

 

[Anonymous-0]

Beest I've found says it was company custom that chose the ground. Some makers were positive ground, some were negative ground in the 6 volt days.

Some of the arguments were based on corrosion from experiences with water and sewer pipes along electric RR, trouble with that argument is, the corrosion or erosion problem depends which end of the circuit it is. The direction of current is opposite from the pipe far from the power house as it is close to the power house.

Fact is either polarity worked. But confused people and with solid state electronics it was more bother to make dual polarity radios but I've owned some so it wasn't impossible. Two way radios were made first and longest with reversible polarities both tube and solid state.

I think eventually SAE set a standard and the auto and tractor makers followed the standard which simplified training of mechanics.

But then there were the JD diesels with a +12 and a -12 pair of load circuits to allow 24 volt charging and starting.

Gerald J.

 

[JDemaris]

It's no mystery. With electrical engineering - some older schools favored the Hole Theory which promoted positive ground for less corrosion, and other schools liked the Electron Theory better - which favored negative ground. None has ever been proven to be better overall - but pos. or neg. can reduce corrosion in certain applications - and pos. ground is still used in some of them.

 

[JDemaris]

I forot to mention. In regard to your comment

"If any out there knows of a definitive refernce, I'd love to see it. I have a book from the 1920's which describes automotive electrical system operation, and it is silent on the issue of polarity."

Many older auto, tractor and electrical theory books discuss polarity a lot. Some older auto electric systems used polarity changers and switched back and forth to equalize metal transfer. For references - I have many - but here are a few:

Dykes Automobile and Gasoline Engine Encyclopedia 1838, 18th edition. Discusses polarity a lot and shows diagrams of many polarity changing systems used in cars and trucks.

Audels New Automobile Guilde for Mechanics, operators and servicemen 1941.

Self-propelled Vehicles by J.E.Homans, published by Theo. Audel and Company 1905.

 

[jose bagge]

This British went with positive ground 12V on most of their vehicles (Jags, Triumphs, etc)- but then they also have the steering wheel on the wrong side.

The British drink warm beer because they have Positive Ground refrigerators.

 

[teddy52food]

With a magneto, you will have 2 plugs that fire from the center to the outside. The other 2 fire the opposite. It really makes no difference.