Secondary Light Problems

[morebikes]

I am running 2 B&M Lumotec round headlights from a Schidt Dynohub.
The secondary light was bought from the USA pre-wired for this role.
Both lights will work down to about 9 mph. When moving along at an average speed of around 13-14 mph with both lights on, after a period of time they will both suddenly cut out. As soon as you turn off the secondary light, the primary comes back on, and you can then turn the second light on again, providing you have not lost to much speed by being in the dark.
Can anyone explain why this happens, and any potential cures?

[JonHammond]

I don't know about secondary lighting, but if you're running two lights from one 6v generator, aren't you going to overload it?  It's only a guess, but is it possible that the Schmidt Dynohub is clever enough to include an overload cut-off device in its circuitry?

Let's say your lights are 0.4 amps, and you're generating 6 volts at 3w (again, guessing, but this is fairly normal), then you'll end up drawing 4.8 watts from a generator rated at 3 watts.  Unless there's something about secondary lighting that I don't know.

[jbay]

Most bicycle generators (which are A/C devices - alternators - and thus not dynamos (which produce D/C)) are claw-pole generators. To a first approximation, these are constant _current_ devices. That is, they produce 0.5A and it is the voltage that varies with speed.

Thus, if you go fast enough, you can power two headlights in series. The generator in this case will be producing a nominal 12V, 0.5A or 6W.

The Schmidt hub doesn't contain any voltage regulation circuitry. Open circuit voltage is 100+V if memory serves.

Regarding "morebike's" problem, have you tried putting in fresh bulbs? That is certainly the first thing I would try.

-- John

[matthews2398]

quote:Originally posted by morebikes

I am running 2 B&M Lumotec round headlights from a Schidt Dynohub.
The secondary light was bought from the USA pre-wired for this role.
Both lights will work down to about 9 mph. When moving along at an average speed of around 13-14 mph with both lights on, after a period of time they will both suddenly cut out. As soon as you turn off the secondary light, the primary comes back on, and you can then turn the second light on again, providing you have not lost to much speed by being in the dark.
Can anyone explain why this happens, and any potential cures?

[matthews2398]

From a Schmidt dynohub I run a Busch & Muller Lumotec Oval Senso Plus halogen dynamo front light with standlight & switch 2.4w bulb as my primary headlight, at the back of the bike a Muller D Toplight plus rear dynamo light with standlight. As my secondary headlight I fitted a Schmidt E6-Z front SECONDARY dynamo lamp with 3w bulb. To quote the blurb frorm the website "The E6-Z features a capacitor to raise the dynamo voltage at lower speeds. This lowers the speed where the two lights together have a higher output than a single one from 12 mph to about 10 mph".

My only observation is that it works a real treat and I for one am delighted with it

[JonHammond]

Ah, so they're wired in series eh?  You just need to peddle harder to raise sufficient voltage.

I've got the same lighting setup at matthews2398, but powered by a Shimano generator.  It all works a treat, and I'm very pleased with it.  More light would always be welcome, but there's no way I'll be doing a minimum of 10/12 mph, so my secondary lighting is a very bright white Cat-Eye LED light-cum-reflector at the front, with a similar red one at the back.  I set the LED lights to flash, 'coz I reckon that makes me more visible.