Negative earth v positive earth

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cococola
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Negative earth v positive earth

Post by cococola »

Following on from my post of alternator v dynamo as a similar type thread I wonder if many owners have changed from Positive earth to negative earth or just stayed as original.
If still original have you had any issues with maintaining/using your Minor?
What are the plus v minus of either set up please ?
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myoldjalopy
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Re: Negative earth v positive earth

Post by myoldjalopy »

Similar answer, really - as my car has functioned perfectly well as a positive earth car in the 22 years I have owned it, I have never bothered changing either the polarity of the car or swapping out the dynamo for an alternator. The only caveat to this is that I have had modern repro control boxes fail more than once, which has made me consider fitting an alternator but, as fitting a new control box was easier and quicker, that's what I did 8)
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Re: Negative earth v positive earth

Post by ManyMinors »

Same for me. My Morris has remained dynamo equipped and positive earth since the 1950s and is still functioning perfectly well. Can't really see much advantage to be gained from changing it for my purposes. I like the simplicity of the car as it is and it suits my requirements.
However. those who wish to modernise their cars, I believe find it difficult to obtain radios, satnav sockets and other accessories as well as alternators without converting their cars to negative earth, so many Minors will have been changed to negative earth now. There is no downside as far as I know but all electrical work should be carried out to a good safe and tidy standard. I have seen a few very poor electrical modifications and installations in the past on older cars! :o
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Re: Negative earth v positive earth

Post by KeithL »

Ours was negative earth when we bought it. Never had any problems although I doubt I would have bothered changing it if it had been positive earth.

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Chief
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Re: Negative earth v positive earth

Post by Chief »

ManyMinors wrote: Sun Jan 09, 2022 9:14 pm I believe find it difficult to obtain radios, satnav sockets and other accessories as well as alternators without converting their cars to negative earth, so many Minors will have been changed to negative earth now.
Mine went negative with the alternator conversion, and I presume will have to stay negative regardless of whether it goes back to a dynamo, because of the modern towbar wiring unit.
Last edited by Chief on Sun Jan 09, 2022 9:48 pm, edited 1 time in total.
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Re: Negative earth v positive earth

Post by MCYorks »

As people have already said, both positive and negative earth systems seem to work equally well. In fact a lot of old automotive electrical equipment wasn't polarity sensitive, and would work on either positive and negative earth systems.

The main issue is when you want to fit modern equipment or accessories. As almost all modern automotive electrical equipment; radios, electronic flasher units, alternators, ECU modules and some motors, are designed for negative earth. This is the primary reason for people converting to negative earth.

You also have to beware that positive earth can catch people out, as most people younger than a certain age, have probably never seen a positive earth system :wink: . Take extra care when using jump leads between positive and negative earth vehicles. Check the polarity and be sure the vehicles do not touch each other otherwise a short circuit can occur :-?
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Re: Negative earth v positive earth

Post by cococola »

All very informative and interesting comments again thank you :D

I have just purchased a 1963 pull starting, positive earth Convertible and I would like to keep it as standard as possible except for fitting the following (if possible)
Smiths temp gauge.
12v socket for various requirements when needed.
1.Would it be straight forward fitting these items and possibly other items in future or would I need to convert to neg/earth ?
2.Things to watch out for in future when staying with pos/earth and dynamo?
3.Do I have to buy items electrical as pos/earth?
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Re: Negative earth v positive earth

Post by kennatt »

was'nt there some suggestion that negative earth cars were more resistant to rust than + earth.Or am I thinking about something else.
simmitc
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Re: Negative earth v positive earth

Post by simmitc »

I believe that in the very old days, some manufacturers used +ve earth and others -ve earth. Why? Because they could; but it did lead to some confusion. It also tended to vary from country to country. There then came an industry agreement that everyone would use +ve earth, which later changed to -ve earth. Looking at the effects, it goes back to schoolboy physics with cathodes and anodes: one is always going to be slightly sacrificial to the other.

With +ve earth, the car body is going to be sacrificial, but the wiring and switch contacts should be long-lived. -ve earth protects the body, but the wiring and contacts are more likely to corrode/ Which you prefer is a matter of debate. The amount of corrosion is usually very limited, and may be affected more by dissimilar metals being in contact with each other. Consider which is going to be affected most by losing a few grams of metal: 1/2 ton of body shell or 2 kg of wiring but also, which is easier and cheaper to replace if it does succumb to corrosion? Remember also that the effects will take many years to be seen.

For Minor owners, the choice is really between originality and use of accessories. If fitting a socket of any sort, consider whether you want it to be +ve or -ve on the case, and if that is different from the car, then make sure that the socket is electrically isolated from the body of the vehicle. It would be a good idea to label it so that you don't get confused.
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geoberni
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Re: Negative earth v positive earth

Post by geoberni »

Simmitc has summed it up nicely.
There are arguments both ways, and also a complete load of garbage written too.

I found this written on an American Motoring Q&A Forum, and some of it is hilarious. It's dated 2017....
I've highlighted the funniest bits....

Thirty years ago I asked the same question to an automotive engineer. Thirty minutes later his answer was complete. In the beginning there were basically two - Ford and Chevy. Ford was positive ground, Chevy was negative (mostly). When the ASAE (in the 50's I think) met to establish conventions, the big guy won. However, when you consider the electro-motive series of metals, negative ground is incorrect. Japanese and British manufacturers stick with positive ground in cars they manufacture for domestic sales. The advantages of positive ground lie mainly in the sacrificial anode being the vehicle itself. A few grams of lost iron is less devastating than the loss (or corrosion) of the brass or copper connections in the vehicle. I've seen electrical connectors on the doors of 30 year old RR's look just like the day they left the factory. The switch to 12 volts was a matter of economy (and watts required) to run starters and accessories. Small wires are cheaper. Unfortunately corrosion (think electromotive series again) is squared when the voltage doubles. Negative ground vehicles require a lot of grease and isolation from moist air to remain intact. Positive ground will always be better- but the big guy (GM) won. Conventions have been set that will be next to impossible to change. (Think Metric - that will never become standard here or in the UK. ) Think BETA vs VHS. BETA is better. But guess what- we like quantity over quality. In this case, the consumer made the decision. In the case of negative ground, GM bullied that without any convincing arguments. 12 (and 24) volts were wanted by everyone. It's cheaper. No argument there. Remember, Ben Franklin got positive and negative wrong. This was done because we didn't know what electrons were yet. 50 - 50 guess. Just got it wrong. Japan and UK got it right and are keeping it that way. When our cars rot away, we just buy a new one. Let me get off this little box I'm standing on.
His claim about 30 year old Rolls Royce's doesn't hold up because RR switched back to Negative earth with the Silver Cloud of 1955, all models being -ve earth by the mid 60s. So in 2017 he's need to be looking at RRs muck older than 30 :lol: It's great what you can find out from accurate research :wink:

A fascinating bit of info on this site, the RROC of Australia....https://rroc.org.au/wiki/index.php?titl ... l:Polarity
With the S Cloud series and all models since, the Company reverted to negative pole of the battery to frame although their reasons had nothing to do with the radios. Let me quote from the RREC 1978 Technical 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"

The RR Service Sheets dated 1960 detail the problems of radiators being choked by silt (mostly iron oxide from the block) being deposited by electrolytic action. A system of braided bonding straps was developed from the generator to the radiator to try and reduce this problem and finally the generator was electrically insulated. The cause of these problems was, of course, the positive frame so that is why the company changed polarity to negative frame.
So, more likely to get a blocked radiator with Pos Earth..... :o
Basil the 1955 series II

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JOWETTJAVELIN
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Re: Negative earth v positive earth

Post by JOWETTJAVELIN »

There may be some truth in GM pushing for Negative earth to increase vehicle corrosion. Their engineering in the 1950's and 60's was first rate, but that doesn't sell future cars.
cococola
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Re: Negative earth v positive earth

Post by cococola »

So with regards to fitting a 12v socket to my positive earth car would I still connect the red to a live and the black to an earth in the standard way, as well as wiring up my temp gauge in the same way?
I maybe over thinking this...or maybe not
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Re: Negative earth v positive earth

Post by don58van »

So with regards to fitting a 12v socket to my positive earth car would I still connect the red to a live and the black to an earth in the standard way
No! If you were to do that, you would be delivering a -ve supply to your devices' +ve input and vice versa.

Some devices you power from a 12v socket (presumably the cigarette lighter type) would be OK. For example a DC electric motor would be OK but would run backwards. If it was driving a a personal fan for example, it would suck instead of blow :o .

Anything you electronic you power from a socket wired as you describe in a +ve earth car at best will not work and at worst will be damaged. With electronics, positive must be wired to positive, negative to negative.

So wire the socket the reverse of your quote above.

As for temp meters, I don't know what is inside the sensors so I can't comment. I think it is most likely that the meter/sensor will be polarity sensitive.

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Re: Negative earth v positive earth

Post by oliver90owner »

DC electric motor would be OK but would run backwards. If it was driving a a personal fan for example, it would suck instead of blow :o .

Really? How many have changed from positive to negative earth? How many have changed anything on the starter motor? I think that is a DC motor. Even the dynamo, which is DC, does not need any physical change when converting.

Requirements are different, depending on installation and devices driven. It is beyond the scope of the OP, I think, to sort it out without a few (possibly expensive) errors.
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Re: Negative earth v positive earth

Post by don58van »

Even the dynamo, which is DC, does not need any physical change when converting.
Depends how you define physical. When changing, the dynamo has to be 'flashed' to change its magnetic characteristics, thus making it charge correctly.

I take your point about the starter motor.

I suppose my main point is that non-electronic items like DC motors and 12v electric jugs are generally OK (ie they will not be damaged but some may not work as expected) regardless of how the socket is wired. However, the correct polarity should be observed when connecting electronic devices.

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Re: Negative earth v positive earth

Post by simmitc »

An older temperature gauge will be s simple moving coil device and will work fine either way. More modern gauges have electronics in them (digital display, warning lights, buzzers etc) and they will be polarity conscious, and so will not work on the wrong earth.

For your socket, it MUST be isolated from the car body. Use a wooden or plastic mounting block. If the socket already has two wires attached, then connect the red wire to the car body using an inline fuse and the black wire to a supply wire on the car. Depending on where you connect to the supply, it could be brown or green. Consider what load (watts or amps) you want to place on the socket and ensure that the socket is rated accordingly and that the wiring you use is suitable.

Also consider whether you want the socket permanently live or switched via the ignition. You may need to supply the socket via a relay.

If the socket has terminals rather than wires attached, then connect the centre terminal to a red wire and the body to a black wire, and then proceed as above.
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Re: Negative earth v positive earth

Post by jagnut66 »

Going back to the title, negative earth will be required for many modern additions (like a power socket and a radio), so like the alternator discussion, it a case of 'horses for courses'.
Some will want total originality, some will want to add a few things to their cars.
It's the way its always been with 'classics' (of whichever Marque you are lucky enough to own).
I don't think there is any 'right or wrong', if a person owns a car it's their choice. Other may not like it it and that is theirs.
So long as both are welcome here the club will continue to thrive.
Best wishes,
Mike.
1954 Series 2: 4 door: "Sally" -- Back on the ground with (slave) wheels and waiting to be resprayed......
1970 Triumph Herald 1200: "Hetty" -- Driven back from Llangollen in Wales (twice.....)
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Re: Negative earth v positive earth

Post by geoberni »

oliver90owner wrote: Tue Jan 11, 2022 8:20 am DC electric motor would be OK but would run backwards. If it was driving a a personal fan for example, it would suck instead of blow :o .

Really? How many have changed from positive to negative earth? How many have changed anything on the starter motor? I think that is a DC motor. Even the dynamo, which is DC, does not need any physical change when converting.
Very much depends on the type of DC Motor. A permanent magnet motor , yes just switch the supply around.
With a 'standard' design motor, i.e. one with Field Windings and an Armature supplied through brushes, you need to change the polarity or either of the windings. If you change the polarity of both, as in when you change the polarity of the car, then there is no change in direction.

The Flashing of the Dynamo is just to give it a bit of a kick in the right direction when the system is changed over. A week or so ago I was conversing with a Newbie Owner on the facebook Group.
His post had started off...
First drive out in Keith today, after sorting the poor running, turned out the last owner had put the connected the battery back to front??,,Car runs really well, Drum brakes are vague , Can anyone recommend any up grade to the drums to make them more powerful.
So I asked the obvious, since those posting before me has just focused on the brakes question.....
"turned out the last owner had put the connected the battery back to front??,"
Why is that relevant to 'Poor Running'?
It will affect the charging circuit, but not the engine.
Why do you say it was incorrect?
All Minors were built Positive Earth, but many have been changed to Negative Earth over the years because of people fitting Alternators or even just having a +ve earth radio fitted.
So which way around is your battery now fitted?
Have you got an Alternator or Dynamo?
To which the reply came....
... the battery was connected negative connection to the positive post on the battery when I took delivery of the car, it lacked any power and wouldn’t tick over properly, without going into anything else, simply by swapping the connections to what appears to be the correct way around it’s made a difference to my car, tick over is now correct, and the car drives better,I will need to check if it has an alternator, I assume that if that is the case you allude to advising it needs to be changed ?? Thanks
I explained how things should be done, but he hasn't come back since, aside from asking if Points were polarity conscious....

So he reversed the polarity without flashing the Dynamo and apparently didn't get a IGN warning Light, so the dynamo must still have charged the battery, despite not being 'flashed'. :roll:
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cococola
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Re: Negative earth v positive earth

Post by cococola »

Going back to my question..The items that I would really like to wire up are..
Old fashioned Smiths temp gauge and a 12V socket
I did consider a radio/cd but I guess that I would need to start considering alternator fitting..In which case Im not so concerned having the music system.
How do I wire the guage and the socket whilst staying as positive earth OR do I change to neg/earth if it makes things easier?
The 12v socket would use a dashcam and phone charger, so with the wiring up this may need to be taken into account.
I also have one of these cut off switches with the big red key that would be nice to fit as it was bought as a present.
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Re: Negative earth v positive earth

Post by jagnut66 »

The Smiths temp gauge would probably work but I suspect that the modern 12V charger outlet will need to be negative earth if you want to recharge your phone or run a dash cam from it.
Personally I'd go negative earth for all round compatibility, however it's up to you.
Best wishes,
Mike.
1954 Series 2: 4 door: "Sally" -- Back on the ground with (slave) wheels and waiting to be resprayed......
1970 Triumph Herald 1200: "Hetty" -- Driven back from Llangollen in Wales (twice.....)
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