Positive earth

[Russ]

Can someone please explain why my 51 A10 is Positive Earth. I realise the positive terminal goes to earth but don't understand why it is done this way.
Thanks Russ

[Topdad]

Hi Russ , I'm not qualified to answer the tech side of this but as you're online thought I'd reply , I think it was the original why that cars and bikes evolved . I can remember when selling bikes and cars in the '60,s amd 70's that cars and bike moved from pos earth to neg earth and back again until it seemed to settle on neg earth . Maybe because components like alternators quickly replaced dynamos and pos they responded to neg earth or something simple like less resistance at earth points do to less corrosion with neg earth . Certainly remember something like that being voiced in the past , however hang on some of the elecy wizards will enlighten us when they come online regards BobH sunny liverpool ( for once ) 

[a101960]

Can someone please explain why my 51 A10 is Positive Earth. I realise the positive terminal goes to earth but don't understand why it is done this way

All to do with a theory that battery terminal and chassis corosion would be less of a problem. In practice the theory was found to be flawed. So, vehicle earthing reverted to negative earth.

John

[BSA_54A10]

As John stated it was an extension on the cathodic protection that was used on steel hulled ships.
It does actually work, but only when the bike is immersed in salty water.

[Greybeard]

As John stated it was an extension on the cathodic protection that was used on steel hulled ships.
It does actually work, but only when the bike is immersed in salty water.

So, a normal winters day ride here in the UK.

[Russ]

Thanks Guys.
Do I leave it as Pos earth or is there a benefit in changing to Neg earth, assuming that can be done.
Russ

[a101960]

Do I leave it as Pos earth or is there a benefit in changing to Neg earth, assuming that can be done.

Russ, for all practical purposes it really does not matter whether you opt for positive or negative earth. The main advantage of negative earth is that it makes it easier to fit LEDs if you wanted to (tail lamp, parking lamp,and speedo lamp fpr example). For negative earth set up connect the negative terminal of the battery to the frame, and reverse the ammeter connections ( if you already positive earth). The opposite applies for positive earth. You will also need to "flash" the dynamo field coil to suit the polarity you opt for. To flash the dynamo field coil disconnet the green wire from the dynamo and with a spare bit of wire connected to the green wire, then just touch the other end of the wire to the battery terminal that you have choosen as your positive feed ( that is to say the battery terminal that is conncted to the loom. Not the terminal that is connected to the frame). Thats all that is needed. You will find it easier to disconnect the green wire from the regulator rather than faffing about taking the cover off the dynamo.

John

[muskrat]

 I'd leave it +ve just because that's the way it was. I use red for the earth wires just in case someone else attaches a charger or other device.
Cheers

[sparx]

I've been an auto-electrician all my working life, about forty years now, but I confess to often getting confused when doing fault diagnostics on a positive earth car or bike.
 I don't think I'm alone in expecting the supply to a component (lamp or whatever) to be positive. It seems kind of alien to me that the "supply" from a dynamo is negative (sink, to use electronics speak) rather than positive (source) when the bike is wired positive earth.

[bsa-bill]

As sure as I can be about a 1950 - 60 ish article the reason for positive earth was to reduce the deposition of metal on the points ( the pip you were advised to file off at regular intervals), this being to do with the direction of the current.
Now to my innocent mind it would seem logical that all that would be achieved would be the deposition of the metal onto the other side of the points

Other theories are available - tho

[Triton Thrasher]

I've been an auto-electrician all my working life, about forty years now, but I confess to often getting confused when doing fault diagnostics on a positive earth car or bike.
 I don't think I'm alone in expecting the supply to a component (lamp or whatever) to be positive. It seems kind of alien to me that the "supply" from a dynamo is negative (sink, to use electronics speak) rather than positive (source) when the bike is wired positive earth.

I suppose you know that electrons travel from negative to positive.

[sparx]

In common with the vast majority of people I always think in terms of conventional current flow, positive to negative, rather than electron flow.

I suppose you know that electrons travel from negative to positive.

[KiwiGF]

If you change polarity you may also need to get a new electronic regulator, if one is fitted eg like the dvr2.

[A10Boy]

In common with the vast majority of people I always think in terms of conventional current flow, positive to negative, rather than electron flow.

I suppose you know that electrons travel from negative to positive.

Hold on a G'damn cotton picking minute. If the Current flows from Pos to Neg, how can electrons go Neg to Pos? When I was at school, I was told to think of an electrical current as water flowing through a pipe so if the electrons are going the wrong way, do they know they are swimming against the tide or what ?? 

[bsa-bill]

Now then A10boy were getting into physics here - so from a farm boys study of turnips I have discovered (actually by watching Prof Brian Cox and attending our local U3A science section)

Electrons are negative, Protons are positive, Neutrons couldn't care less
So possibly (someone correct me if wrong) electrons will travel from the negative terminal to balance the positive charge at the other end due to natures dislike of an imbalance.
So again possible our definition of current is a bit ambiguous in as much as it's not like a flow of water or substance but a leveling out of bits of atoms.

On the other hand it could be smoke right enough