Forum

[Lardmarc]

Hello men. It turns out that I've purchased an early 350 export bullet. It's 6 volt positive earth, is their any benefit by converting it to 12 volt negative earth ? I don't want to just throw money at it for fun but if their is a definite advantage I don't mind.

[John M]

The biggest advantage is that the wiring for properly regulated 12V systems is far simpler, 12V parts and bulbs are more common if you need spares in a hurry, you can use modern 12V voltage regulators and rectifiers and it would enable you to switch to electronic ignition if you wished.----------- 6volt systems have a weird and wonderful switching system because old voltage regulators were not up to the job of regulating and the alternator's coils were switched in and out depending on the requirements. -------- You can convert to 12 volts using your existing 6volt alternator. ---------- Have a look at the BSA site at http://www.bsa-c15.org.uk/c15_12v_conversion.htm this has more info.

[Thack]

I agree with John M: it's a pain in the arse finding 6V bulbs and the like these days. Also, 6V lights are dim because you need twice the current for a given wattage, which doubles the voltage drop through the loom and across any weak connectors. The polarity of the earth makes no practical difference, but moving to 12V will. Take a look at the Boyer Bransden Power Box, which our hosts sell: http://www.hitchcocksmotorcycles.com/ac ... s-charging. You can read more about it here http://boyerbransden.com/PBdynamo.html.

[neddy]

Always thought the polarity of the "earth" made a difference to the rate of corrosion of the components on a motor vehicle, is this true ?.

[Thack]

The polarity of the earth affects things like lead-sheathed underground cables, and such, but that is different because the lead is in direct contact with the earth. There was a rumour that positive earth caused vehicles to rust more quickly, but I don't think anyone takes that seriously these days - they physics doesn't support it. Apparently negative earth became adopted simply because the motor manufacturers had to adopt one or the other as a standard, and the introduction of car radios (based upon existing designs) was easier with a negative earth. In reality, neither terminal is earthed, because the tyres act as insulators so the vehicle "floats" electrically. Really it's just a convenient form of terminology - it ought to be called "chassis" rather than "earth". Anyway, it doesn't matter to the chassis which way electrical current flows through it. HOWEVER - any current that flows from one metal part to another can cause electrolytic corrosion at the point where they touch (regardless of which way the current is flowing), so these days cars and motorcycles tend to use earth wiring, rather than relying on the chassis to act as the return. Thus corrosion is reduced.

[Lardmarc]

I was admiring a C15 today while getting my other crate MOT'd. Thanks for the link, that should be an easy conversion. The positive earth had me worried because of wanting to get rid of the points as the previous owner had made up his own backing plate in the alternator which doesn't work. Electronic is the way to go. I'd heard about positive 'chassis' vehicles being prone to rust but looking at my new acquisition I'm pretty certain that the previous owner had stored mine in the sea.

[John M]

The whole positive earth thing appears to have been a fad of the late 60's early 70's British motor industry. My mate has a 1967 BSA and a 1972 Triumph both of which were positive earth. We converted the BSA to negative earth when we rewired it just because you don't have to think as hard when the wiring is normal. As for the Triumph I managed to get an impressive amount of smoke from the loom when I connected a booster pack to it using the engine as an earth..........oops!--------If your budget is tight you can use a four wire rectifier/regulator from an old jap bike rather than splashing out on a new one.They seem to use a universal colour scheme where two yellow wires are the feed from the alternator and the red and black wires are regulated 12v out, couldn't be simpler.-------One of my Bullets uses a universal rectifier/regulator, Eureka electronic ignition and a Lucas 2MC capacitor rather than a battery. This makes a simple electrical system that does not rely on a charged battery for starting, however no engine = no lights.

[simon]

I've kept mine 6v and I have lovely white lights and no issues getting the bulbs. Our host have them I believe and they stock stop/ tails for things like Honda 100's at the local bike shop so no real problem there. I did replace the stupid switch charge system for a Pazon Regulator/Rectifier which they supplied in 6v spec. I have a mag ignition so it's only running the lights but it's fine in + earth with a little 6n63b battery tucked into a wooden box that I made to look like a pitch battery box.

[Dennis C]

The old adage applies, "if it aint broke don't fix it".

[Dennis C]

Why do thing dissapear from my posts?.

Or in the case of a lot of Enfield owners thinking. Keep fixing it until it breaks.