Two dyno lights, one switched…?

[Brucey]

having said that, some lights will spit DC out to the rear light, and you can also buy LEDs with a series resistor inside that means you can attach them to 12V directly. These will light up with 6V, just not as bright, which might be what you want anyway.

cheers

[stewartpratt]

So the remaining question, I think, is where to attach the rear light. It would be very convenient if it worked when simply connected across the dip beam. Would I be right in thinking that this would be fine in practice? At high speed there should be enough voltage; with the high beam switched off it's basically a normal single-lamp setup anyway; and if I was to, say, slog up a short, steep climb without bothering to turn off the high beam then the standlight would cut in anyway…?

[Brucey]

yup, in parallel with (or using the output connection for) the dip beam, as I suggested earlier.

cheers

[stewartpratt]

Oops. Must have missed that; sorry

[MikeF]

So the remaining question, I think, is where to attach the rear light. It would be very convenient if it worked when simply connected across the dip beam. Would I be right in thinking that this would be fine in practice? At high speed there should be enough voltage; with the high beam switched off it's basically a normal single-lamp setup anyway; and if I was to, say, slog up a short, steep climb without bothering to turn off the high beam then the standlight would cut in anyway…?

It depends on your slogging speed, but you should find both lights will still give light from the generator even if shimmering a bit. I am using (but not very often) your proposed set up on one bike and I find you only 1-2mph more for both lights to work than for one. One thing I haven't been able to determine is how the rear light is connected internally in the headlight eg is it just in parallel or is there circuitry involved - series across a shunt? - and does it differ between different lights? Anyone know? It seems to me there has to be more current going through the high beam than the dipped beam as the dipped beam is sharing current with the rear light, so the high beam will be brighter.

It may seem obvious but before you start out, you will need remember to turn on both headlight switches. If you don't and you open the shunt switch for high beam you will suddenly be in darkness. You could, of course, always leave one permanently on as long as, when you finish, you don't might it remaining on until the standby capacitor is discharged.

Let us know how it works.

[tatanab]

It seems to me there has to be more current going through the high beam than the dipped beam as the dipped beam is sharing current with the rear light, so the high beam will be brighter.

The amount is trivial. I think I remember a sheet with my rear light (Philips) which said 30 or 40 mA. The front light takes about 15 times that. Given the human eye response to "brighter" I very much doubt you will detect a difference.

[MikeF]

Probably depends what rear light you use. The Philips Lumiring states 0.6W which would be 100ma and would a quarter of the current going to the headlight. I thought the "standard design" split was 2.4/0.6W front/rear for a 3W generator, but what happens in practice I don't know. I think 40ma might be an underestimate for a rear light, but the only accurate way to test is with an AC meter. Something I should do but practicalities have so far got in the way! Using DC I found a Secula Plus light took about 70ma IIRC.

[Brucey]

older rear lights draw 100mA but most new ones don't. Mine is extremely bright and draws less than 30mA.

cheers