Positive vs Negative ground. Is there an engineering reason?

[Tonz]

I've had lots of experience with my 1949 BSA A7 500 twin.

It like most Pommy bikes of the the day they were 6v pos earth.

A few years back the time came to renew the full charging, regulator system and thanks to a great following of enthusiasts I could buy the Lucas E3LM dynamo rebuild kit and solid state regulator/ cut out for about $300AU.

Wassell's of England supplied the kit with plain speaking instructions and it still works perfectly today.

 

Interesting point is just but ticking the appropriate box when ordering I had the option of 6v or 12v, neg or pos earth.

 

The instructions required me to use either one brush in the dynamo or the other for the polarity change. And the field winding connected the correct way. 

Interesting to note that absolutely nothing will work on a new dynamo until you tickle or excite the field wires🤨

 

[37_Roadmaster_C]

@Tonz, Your note at the end is like us in the car world talking about "Polarizing" the generator. Same end effect and result.

[thomas gaskins]

thought i would add my 2 cents worth i read a few years age that the reason for positive ground was when the industry moved to metal wheels they  thought the battery might discharge to ground from the carbon in the tires. that being said i learned to drive with a 65 hillman husky with positive ground. so habit and a reluctance to change also figured in 

[Frank DuVal]

To discharge a battery, there needs to be a complete circuit. Connecting one battery terminal to the earth is not a complete circuit.😉

[Bloo]

In the teens there was no standard. It was fairly common for there to be a floating ground. Ground return wires were used for everything in that case. I have a 1913 Studebaker that requires it. There is no electrical starter, only a Splitdorf hotshot magneto that uses 6 volts, originally from dry cells, for starting. Splitdorf literature is explicit that the primary side (batteries) cannot be grounded, since the engine (and thus the spark plugs) are grounded. Engines were usually mounted directly to the chassis in those days and my Studebaker is no exception. Some other Studebakers of this era had electric start, a hotshot magneto, a 12 volt starting and charging system and they ran 6 volt lights on it. I imagine the grounds were floating. 9 volt hotshot systems also existed at that time.

 

In those days the starting and charging system and the ignition system were likely to be from different vendors. Never mind the lights. The automaker did whatever was necessary to make all that play nice. If I am not mistaken, I have seen a wiring diagram for some car that had both dry cells (for a hotshot magneto) and a lead acid storage battery. A quick flip through a wiring diagram manual for teens and 20s cars will definitely surprise you.

 

A starting and charging system is likely to be grounded rather than floating because the starter is bolted to the engine. It wouldn't have to be connected electrically but it often is. The manufacturer of the starting and charging system in that case would be driving whether the system is positive or negative, and whether it is 6 or 12 volts.

 

In the mid teens, Hupmobile went from a 6 volt to 12 volt and back to 6 volt within the space of 2 years as they changed starting and charging systems. I believe the grounding changed during that time as well.

 

An interesting question to ask is why the Model T Ford is negative ground, and the Model A Ford positive? In that case it is likely that Ford engineered both systems, and was not at the whim of an outside vendor.

 

 

 

[PFitz]

Ford was not the only one in the later 1920s to change from all production neg ground to all pos ground, so I wonder if it was a recommendation from another source other than an auto manufacturer, such as maybe the SAE ?

 

Paul  

[Larry Schramm]

3 hours ago, Bloo said:

If I am not mistaken, I have seen a wiring diagram for some car that had both dry cells (for a hotshot magneto) and a lead acid storage battery.

 

You are not mistaken.  Here is a wiring diagram for my '15 Buick truck.  It has a 6 volt battery & 10 volts of dry cell batteries.

[RAH]

Guys, (and Gals) BOY there has been a whole lot of redundant and confusing hyperbola here. I have been in electronics for as long as I can remember or learned what an electron IS! Perhaps this a bit off the initial subject of which GROUND system has any obvious benefit. I spent 44 years servicing Electronic ORGANS and Keyboards and do specifically recall one Tech Service Meeting by a tech rep for (an unspecified Model) where they were introducing NEW computerized solid state circuitry on individual P.C. boards. The rep stated up front that we are going to use the conventional theory that current (electron flows) from positive to negative. I just sat there for a microsecond and asked " Fine for these boards BUT what about INSIDE the Power supply?" There was a moment of silence then his response was "Shut up Hartley and set down" One other take on the subject was his insistence that when measuring voltage on ANY individual PC board to make certain the ground lead of the meter was fastened to GROUND on that PC board NOT to the ground on the power supply. His response was GROUND is EQUALLY as important as the POWER lead on that board. AMEN.

[RAH]

Not to belabor the initial OP's query but the word 'GROUND' has NO political aspirations positive OR negative. It is simply a common return point for each of the various and sundry electrical devices in a system (automobile) to complete a circuit back to the power source (positive OR negative). Period!_

[joe_padavano]

On 12/13/2022 at 1:18 PM, Frank DuVal said:

To discharge a battery, there needs to be a complete circuit. Connecting one battery terminal to the earth is not a complete circuit.😉

 

You mean that setting a battery on a concrete floor DOESN'T cause it to discharge???  😉

[Larry Schramm]

1 hour ago, joe_padavano said:

 

You mean that setting a battery on a concrete floor DOESN'T cause it to discharge???  😉

 

Maybe with a rubber case on the old batteries, maybe.  I am not sure it is true or an old wives tale.

 

New batteries with the plastic cases, no they will not discharge.  If left long enough, the internal resistance the battery will eventually discharge.  Probably talking a year or more just sitting there.  IMO.

Edited December 17, 2022 by Larry Schramm (see edit history)

[Tonz]

A battery stored on concrete floors will possibly discharge quickly when you add into the equation damp concrete and a layer of also damp dust over the battery.

Years ago when working in the outback at the end of each day we had to refuel, pop bonnet and clean bulldust off the battery or your vehicle may not start next day.

This is called tracking. Where a heavy due over night is absorbed by the dust etc etc.

Nowadays in winter I store my unused batteries inside the house, warm and dry.

 

Regarding our "experts" who understand electrons etc, I was told by an old motorcycle mechanic that all the wires on British motorcycles were full of blue smoke.

If you break a wire and the blue smoke escapes the bike won't go anymore!😆

[sarookha]

On 12/1/2022 at 10:21 PM, Frank DuVal said:

Because there HAS to be current flow from the zinc back to the steel to complete the circuit. Just hooking a wire from the steel to the zinc is not a complete circuit, and without a complete circuit, electrons can not flow. In the EARTH the electrons flow through the earth to return to the steel tank, completing the circuit.

So then, two cables.  One to the buried anode, the second to a copper grounding rod?  Hook one up to the front bumper, the other to the rear bumper, would that no make for a complete circuit?

[rocketraider]

On 12/29/2022 at 5:46 AM, Tonz said:

 I was told by an old motorcycle mechanic that all the wires on British motorcycles were full of blue smoke.

If you break a wire and the blue smoke escapes the bike won't go anymore!😆

I think that's the case with all British electrical systems. And, to be fair, most everyone else's too!

[Frank DuVal]

9 hours ago, sarookha said:

So then, two cables.  One to the buried anode, the second to a copper grounding rod?  Hook one up to the front bumper, the other to the rear bumper, would that no make for a complete circuit?

The Zinc has to give up Zinc electrons to the solution, with the steel also in the solution. The "battery cell".

[Frank DuVal]

On 12/29/2022 at 5:46 AM, Tonz said:

A battery stored on concrete floors will possibly discharge quickly when you add into the equation damp concrete and a layer of also damp dust over the battery.

Years ago when working in the outback at the end of each day we had to refuel, pop bonnet and clean bulldust off the battery or your vehicle may not start next day.

This is called tracking. Where a heavy due over night is absorbed by the dust etc etc.

Nowadays in winter I store my unused batteries inside the house, warm and dry.

Wet concrete, wet wood, what's the difference? Battery case is plastic since the 60s. Battery collects just as much dust sitting on a piece of wood several inches off the floor as it does sitting on the floor. Yes, tracking is an issue. And wet dust can cause tracking. Unless you have metal dust, then it can be dry. 

 

Warm and dry always best!

[Rusty_OToole]

If you don't believe a battery will discharge sitting on a cement floor try it. I did and here is what I learned.

I wanted to find out if there was anything to this so I left a battery on a cement floor and tested it each day for a week. Nothing happened. So I got busy with other things and forgot it. After 3 weeks I thought of it and tested it again. The battery was dead as hell and would not take a charge. It was finished.

Normally I keep my batteries on a wooden shelf and charge them up every few months when I think of it and they last for years.

I have a friend who thinks I am nuts and keeps his spare battery on the shop floor and he buys a new battery once or twice a year.

Your mileage may vary.

[rocketraider]

Even though it currently has everything but a battery setting on it, my Willard Battery display rack could solve the problem.

 

My habit to keep batteries off concrete was to put them in an appropriately sized clear plastic bin.

[Frank DuVal]

I store mine on the concrete floor or in a car. I do not have issues with the batteries either way. Leave it in either place for a year and you will not have a happy battery!

 

BTW, one test does not make proof, it is just a data point. 

[Rusty_OToole]

Well Frank if you want to buy 100 batteries I will put them on the shop floor and see what happens. While we are at it you can buy another 100 to put on wooden shelves so we can compare. In the meantime I will be keeping my batteries on the shelf as I have for the last 50 years.

[Frank DuVal]

Excellent idea. What's a Go Fund Me? And that's what it will take to end this age old debate. A Consumer's Reports study. We all have one and two battery data points. 

[EmTee]

Is there a dark rectangular "shadow" on the concrete floor where the battery was sitting when you lift it up?  Condensation on the bottom of the battery...?

[1937hd45]

I know nothing about electricity, and understand less with every thing I read about it. Have two people that clime to understand it ever come up with the same answer to a question?

[60FlatTop]

If early cars were wired with early wire that may not have the best insulation it would be better to charge the whole car and let the circuit be completed after the electric load through the wires. Les change of a short that way.

 

Most modern cars take advantage of a charged load and a switched ground.

[Frank DuVal]

18 hours ago, 1937hd45 said:

Have two people that clime to understand it ever come up with the same answer to a question?

Yes. 👍

 

17 hours ago, 60FlatTop said:

If early cars were wired with early wire that may not have the best insulation it would be better to charge the whole car and let the circuit be completed after the electric load through the wires. Les change of a short that way.

Spell check has ruined your thoughts....😁  Les Miserables I say.😉

 

So better to have live wires going everywhere then just switch the grounded lead of the load? That is less of a chance for shorts? No.