AJS & Matchless Owners Club

Hi All

My father wants me to reword his bike which is a g11 , it has alternator but magneto for his ignition.

I need to know what wire to buy I normally buy wire for 6v and I use 14/0.30 8.75 amp wire

But I don't know what wire I should use for 12 volts

Any suggestions ?

Andy

Here's one view for starters Andy . . .
14AWG is usually reckoned to be good for 12v systems, with maybe lighter 16AWG for things like side lights. The heavier gauge for the battery cabling to switch and ammeter, for sure. I think the wire gauge sizing translates into 28/0.30mm and 32/0.20mm (it does - I just checked in James Smith's Big Book on classic m/cycle 'lectrics).
(I think for 6v you might have been under-strength actually. It's not just about current capacity, but also about voltage drop along the way, which is more of a worry at 6v.)
And not forgetting fuses . . . I tend to use 10A for the main fuse on 12v systems. I also always make sure the brake light is in a fused circuit, as they're a common point of failure, what with wires rubbing under mudguards etc.

Remember current drops off as voltage increases so 12v systems will be carrying essentially half the current a 6V system does at a lower volt drop. The cabling should be rated at a much higher voltage than 12v so even using the same size of cabling you were for 6v should see an improvement.

V x A = W
V ÷ W = A
W ÷ A = V

65 W headlight bulb on main beam at 6 V is 10.8 A, but at 12 V is 5.4 A remeber your voltage may vary.

So add up the wattage at a given point a do the maths. I would go for bad battery moment and do the maths for stuff -1V of nominal.

If your worried about the wire taking 6 or 12 V then I wouldn't worry as wire is often good at insulation voltages above 1000 V. The killer of wire is current.

Regarding voltage drop, if you look up wire sizes you will see info about this and it is basically how many volts get lost per given length. DC doesnt do well travelling along wire and tends to lost power fairly quickly. In a car it's common to loose almost 0.5V from front to back. But upping the size of wire can help reduce these losses.

When I did my G3 I think I did most of it with 2mm squared wire with the battery to frame wire as a 3mm because I could. I also ran another wire to the headlight to act as an earth so that I could avoid issues with bad earth at the headlight.

If you ever feel mad enough you could use some relays to wire up the lights as plenty of the electrical power can be lost via switches. I do plan to do some real world current and voltage readings on the bike but yet to be that bored. But I do have a nice DC fluke clamp meter now.