Changing from 6v to 12v

[AngleseyAJS]

Good afternoon everyone,

I have a 1955 AJS 18S and i'm having issues with the dynamo which necessitates it being sent off for a service / refurbishment .

Its currently 6v but my question is should i have it changed to 12v?

What are the pro's and con's to doing this?

Many thanks

Chris

[dave16mct]

Unless you have some specific reason for wanting 12v ie sat nav I would keep it 6v. LED bulbs now available are very good and to maintain your 12v battery you will have to ride your bike faster. I'm considering doing away with the dynamo on my next single bitsa as the LED's use so little current.
Dave.

[AngleseyAJS]

Unless you have some specific reason for wanting 12v ie sat nav I would keep it 6v. LED bulbs now available are very good and to maintain your 12v battery you will have to ride your bike faster. I'm considering doing away with the dynamo on my next single bitsa as the LED's use so little current.
Dave.

The wiring loom isn't terrible but it's been fiddled with and I think I'd really like indicators so I was thinking about making a new one and wasn't sure if it had to be different if it wax a 12v system.

Ive no real reason to go for 12v but brighter lights would be nice!

I'll have to look into LEDs, what do you recommend?

Thank you

[spookefoote1956]

No you don't need to worry about cable size. That really only becomes an issue when you have an electric starter

[dave16mct]

Most members recommend Paul Goff who does most LED types. Lots on Ebay but you have to be carefull. I've had good results from Auxito but they're usually H4 fitting for the headlight so it depends how original you want the bike to look. I'd sooner see where I'm going! They're usually 12v too but a stepdown can be bought on ebay very cheaply. Dynamo and Regulator Conversions have a good range.
Dave.

[AngleseyAJS]

Most members recommend Paul Goff who does most LED types. Lots on Ebay but you have to be carefull. I've had good results from Auxito but they're usually H4 fitting for the headlight so it depends how original you want the bike to look. I'd sooner see where I'm going! They're usually 12v too but a stepdown can be bought on ebay very cheaply. Dynamo and Regulator Conversions have a good range.
Dave.

Thanks Dave,

I'm of the same thinking as you that i'd rather see my way home! I feel like making a new loom could be a bit of fun over winter so i can use all this information to make if future proof.
I also didn't know you can step 12v down so thats interesting too.

Many thanks

[MalcW]

With a 12v system currents are lower for a given wattage, so you shouldn't need to worry about wire sizes. My AJS twin is 12v and the dynamo has been rewound to suit. It also has an H4 headlamp fitted by a previous owner. I tried a couple of LED headlights but although bright the beam patterns weren't great. So now I have a 60w H4 halogen headlight but everything else LED, and the dynamo can easily keep up.
If you do decide to go to 12v to run accessories, e.g. sat nav as Dave mentions, you might want to consider swapping to negative earth as well, to make life easier.

Malc

[Reynard24]

The shorter dynamo fitted to the singles has a lower output than the twin unit and won’t manage a 60w halogen headlamp bulb, however, if you can afford it, the Alton alternator is a direct swap and will power an H4 bulb plus tungsten bulbs elsewhere else so indicators at 12v 21w would not be a problem.
I was also advised some years ago that the short dynamo doesn’t have the space to fit a 12v field coil or rewound 12v armature. I’ve found 6v LED headlamps to be just as good as the 6v tungsten bulbs but the reflector must be in good condition or the beam is too diffused.

[SPRIDDLER]

The shorter dynamo fitted to the singles has a lower output than the twin unit and won’t manage a 60w halogen headlamp bulb,

Quite so.
The 6 volt E3N dynamo fitted to your '55 single has a max output of 42 watts (in top condition at about 40mph in 4th gear) so nowhere near enough to cope with an electrical demand of 60w and the battery would flatten very quickly with lights on.
The 42 watts of power at 6v is a max current of 7 amps but if you uprated to 12v the existing wiring loom would be fine provided that it and all connections were in serviceable condition since at 12v it will only be carrying half the current (3.5 amps) than at 6v. However, as already mentioned the dynamo would need to rotate faster.

It has always struck me as curious that when we want a brighter light in our houses we increase the lamp's wattage not its voltage.

[Groily]

For short dynamos the finer-wound "12v" field coils or armature windings are not produced as 'off the shelf' after-market options. New standard parts are. Best, honestly, to run shorties at 6v.

For E3Ls there are new standard windings and also finer "12v" ones available. The field and armatures have to be used in pairs, no mix 'n match between types. And yes, you can't put long bits in short bodies or vice versa: the long field coils are retained by 2 big screws not one and all the 'L' armatures are a lot L for longer.

The standard "6v"windings will generate up to 80W continuous at 12v in an E3L, but cut-in speed is higher obviously - they're better on twins than singles as the former are revvier. I have regularly run Oxford Hot Hands (35W) + trad 36W headlamp plus tail and speedo in this 12v configuration using a standard E3L on several bikes - so a load in the 75 Watts range. I know folk who run Boyer ignition on dynamo machines, with trad 36W headlamps etc, without trouble. There are no free lunches in any of this though, and loads on field coils are a possible issue when running standard set-ups at 12v and heavy demands. V = iR and all that Mr Ohm stuff. But field coils are quite robust . . . .
One 'standard' dynamo of mine fried after several years, but others haven't.
The only fine-wound 12v set-up I tried died an early death owing to my expecting a bit too much of it.

There are 2 perfectly-respectable schools of thought here (3 if you count Altons) - but I prefer the standard windings as they are less fragile and have served well on twins. Others swear by the finer windings as long as loads are moderated - and if I had a single I probably might too.

E3Ls wound with finer "12v" parts really should not, however, be loaded beyond the rated 60W as the armature wires are thin. The wires will be thrown off the commutator at some point if too much is asked of them. That's what mine did. The max current is a notional 5 Amps, compared to twice that from the original windings.
I would therefore say a continuous load of about 50W is a safe guide in the "12v"configuration - and certainly not the 75-80W mentioned using standard windings, even with a decent regulator.

The short dynamos, eg E3HM and E3N (but probably not E3AR or the original-type E3M from early magdynamo days), can run at 12v using what's in them, but revs are needed to cut in and there is an element of risk. I run one twin with a short dyn (E3HM modded to take the drive end plate necessary for a twin) at 12v with a DVR2, but all LEDs so max load no more than about 3 amps excluding horn. Fitted as an emergency measure when the E3L played up after 10 years' use (the brush-end monkey-metal bearing carrier snapped, the armature went eccentric and there were smells and noises as it self-destructed in quite a big way.) I'm waiting impatiently for the short one to die gracefully so I can put the rebuilt E3L back on, but it's done 18 months of quite heavy use, running with lights on all the time - and is proving stubbornly capable. When she goes she goes, and she'll owe me nothing.

One day, an Alton maybe, but to be honest I've found dynamos to be OK (touch wood) for quite decent mileages if hooked up to decent regulators.