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Old May 3rd 18, 01:25 PM posted to
Sepp Ruf
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Posts: 217
Default Dynamo/LED power conditioning

David Scheidt wrote:
sms wrote:
:On 5/2/2018 7:49 PM, 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
: 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.

The classic B&M circuits used rectification and current-doubling to fully
power one 1 amp led. Your 2x3S LED approach is quite different.
Good luck!


:I suspect that they use a Schottky Bridge Rectifier, with a capacitor
:across the DC output, plus a couple of farads for any standlight that
:switches in when stopped.

I would not be at all surprised if the better stuff (where better
needn't mean 'more expensive' just 'better design' or maybe just
'newer design') is using a MOSFET bridge. One for a bike light
wouldn't be terribly expensive, and they're substantially more
efficent than a schottky is.

Not necessary though, especially at road bike velocity and (switchable to) a
(rectified) 2S max configuration for those rare low speed moments.

Joerg will surely volunteer to build an uber-efficient, but also beverage-
and wildlife-proof circuit for Bob.

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