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Old May 3rd 18, 04:58 AM posted to rec.bicycles.tech
Frank Krygowski[_2_]
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Default Dynamo/LED power conditioning

On Wednesday, May 2, 2018 at 10:49:23 PM UTC-4, 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.


I'm a mechanical engineer, not an electrical engineerm and I can't say about
B&M, but I had one off-brand LED headlight that died by burning up its LED, so I
took it apart and replaced the LED (with great trouble). Turns out the
electronics were simple: IIRC just a bridge circuit, a voltage regulator
and a few miscellaneous components. And again, it failed by cooking the LED.

But I've also opened a low-end B&M headlamp. I can tell you that it had a heck
of a lot more complication in its electronics. Lots of surface mount stuff that
I can't identify. So I do wonder what it all is.

But again, I'm an ME, not an EE.

BTW, I fitted an ancient Sturmey-Archer Dynohub with a high power LED. My
circuit had the headlight and taillight anti-parallel, with no rectification.
So half a cycle goes to the headlight, half to the taillight. It flickers,
but it's not a bother. 20 poles, but above 10 mph I don't notice the flicker
much.

- Frank Krygowski
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