I have just uploaded "Dynamo re-polarization" information I received from Ron Pier and "General Upkeep Hints and Tips for a Famous Old Warrior" from Motor Cycle 1961 I received from John O'Brien to the Technical info page.

Henk.

email (option): ahum@quicknet.nl

Wouldn't it be easier, safer and more "authentic" to simply reverse the battery cables? After all, nothing polarized runs off the electrical system except the battery and the dynamo. The battery and the dynamo simply need to agree with each other, not with which way is ground. And I can't help but think that every time you "repolarize" the dynamo, the magnets' strength is reduced.

email (option): jonny.rudge@verizon.net

The dynamo's magnetic field is produced when current is flowing through the field windings, only a residue amount of magnitism is needed in the pole pieces to start the dynamo working.

Well John it wouldn't be authentic to make a WM20 positive earth! Also the instructions are from Lucas themselves. Back in the 60's-70's when I were a lad, working as a motor mechanic. At that period there was a mix of Neg or Poss earth vehicles. Every dynamo we fitted had to be polarized accordingly. Ron

email (option): ronpier@talk21.com

Vehicle electrical systems use an 'earth return' through the chassis (frame) to reduce the amount of wiring required. Polarities have differed at various times as both +ve and -ve earth systems have advantages.
When coil ignition systems are used the spark plug produces a better spark with positive earth. Also, before the introduction of plastic insulation materials rubber and cloth bound systems tended to leak current to earth. This could lead to corrosion of the vehicle parts at the point(s) where it occurred.
With a positive earthed system the level of corrosion is reduced.
Negative earth systems were employed particularly during the war as it is easier to suppress electrical interference with a negative system. Post war the negative system was deemed more suitable for the various electrical appliances that became common on vehicles. The corrosion issue became much less of a factor with the introduction of plastic insulating materials.
As far as old bikes are concerned today it doesn't really matter which earthing method is selected at the rebuild stage. However, once built, if you have selected an electronic regulator suitable for your system it cannot be run with the polarity reversed..Ian

email (option): julie@wright52.plus.com

Ian I think you ment to say the Positive earth system was deemed more suitable post war. But this was fairly short lived and most, if not all reverted back to Neg earth. Ron

email (option): ronpier@talk21.com

Hi Ron..Positive earth was also very common in the 30's.
Quite right though Ron..many vehicles were positive earth after the war but by the end of the 70s pretty much everything went negative again!...Ian

email (option): julie@wright52.plus.com

they went to negative earth because they found the positive earths caused corrosion in the body work of cars negative earth causes corrosion in electrical connection easier to deal with with a bit of plating/zinc

It puzzels me a lot, this postive negative earth thing because the air positive earth it self negative,
and elektrons flow from ninus to plus, so its pritty confusing to me specaily the corosion bit is odd.

email (option): evandeweerthof@yahoo.com

(I hope I understood you correctly but) Air is an insulator and the earth (the ground) is a neutral conductor, neither positive nor negative. That's why, for example, your house can be powered with only one wire to the mains. The "return" or the other "wire" which would be needed to complete the circuit is, in fact, the grounding wire which goes to the grounding pole, using the conductivity of the earth to complete the circuit to the power station which could be many miles away from the end of the grounding pole.

email (option): jonny.rudge@verizon.net