6v to 12v for headlight?

[Malt_Vinegar]

Hi there people,
Has anyone had an experience with running a 12v headlight on a 6v bike? (Classic Honda with no battery)
I was planning to use a 6v to 12v step up unit to drive the bulbs, there are plenty of step up units on ebay for under £5, they would need enclosing and waterproofing but I figured they would solve my problem.
Any advice is appreciated

 

[Rilot]

I don't see any reason why a step-up wouldn't work as long as the wiring and fuses can handle the current at the 6v end.

 

[Dogbreath]

There are several problems:

On batteryless systems there is often no rectifier and everything is powered from an AC voltage. A DC-DC converter will not work if this is the case, and will very likely be destroyed.

Even if there is a rectifier, since there is no battery it means the system voltage will have a massive amount of ripple on it since it is rectified but unsmoothed AC i.e. the voltage will periodically drop to zero volts (either one or twice per engine revolution, depending on whether it's a half wave or full wave rectifier). A typical DC-DC converter will not work correctly under those conditions, so you will almost certainly need to provide smoothing (i.e. largish value capacitor of suitable voltage rating).

Once you get the supply sorted out, you have to realise that you won't be able to draw any more power from the system than you already are, i.e. if you have a 6v 18 watt bulb at the moment, then you can't expect to step the voltage up to 12v and be able to power a 55watt bulb. A 12v 18 watt bulb will give pretty much the same amount of light as a 6v 18 watt light (maybe a little more in practice as current will be lower, so any voltage drops in the wiring and switches will be lower).

The proper solution to this is to see if a rewound stator is available to produce a 12v supply. These have been made for a number of older bikes.

 

[Malt_Vinegar]

Great advice thanks!
I will look for the stator!