On Thursday, May 3, 2018 at 3:49:23 AM UTC+1, bob prohaska wrote:
I finally caved and bought a Shimano dh-3n72 hub for use on my
exercise bike. It works fine, but the LEDs flicker quite noticeably
at all speeds. The circuit puts series trios of LEDs in inverse
parallel across the dynamo, so each trio lights on alternate half-
cycles. The flicker wasn't visible with the old Soubitez roller,
because it was working at about 6x higher frequency. The circuit is at
http://www.zefox.net/~bob/bicycle/schematic.gif
The point of the design is to eliminate rectifier losses, which are
substantial at low voltage.
The new setup might be ok for fast riding. At low speeds and in traffic
I'm less sure I'll like it and fairly certain bystanders won't like it
at all, especially at night. As a DRL it certainly aids conspicuity 8-)
Can anybody point me to a discussion of what outfits like B&M use in
their dynamo-powerd LED headlights? I've searched intermittenly but
never hit the right keywords.
Thanks for reading, and any guidance.
bob prohaska
Bob, it looks like you're trying to make more light than the dynamo can provide current for: that's just too many diode drops, so try fewer LEDs. I have had my doubts about Busch und Muller lamps in the past, and also the bullying marketing tactics of their fans, but their current Cyo lamp is perfectly adequate, and leaves enough power for the rear lamp. It's probably cheaper than anything as good that you can build, and it has roadable optics with a car-friendly cutoff, a standlight and auto-switching. Sorting that lot out from their circuit, which is full of unknown and unmarked components, will theoretically leave you with the information you want. But how to eliminate what you don't want is the problem.
My experience is that Shimano dynamos, of which the -72 was once the most desirable model, come up to maximum output faster than SON dynamos, that is, provide a steady, useful light at lower speed. So if you see flickering at low speed with a Shimano hub dynamo, you're overloading it.
AJ