Dynamo/LED power conditioning

On Thu, 3 May 2018 02:49:21 -0000 (UTC), 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.

https://bike.shimano.com/en-EU/product/component/deorelx-t670/DH-3N72.html
The spec sheet doesn't say how many poles in the hub. My guess(tm) is
the same as the DH-3D71 with 28 poles. So, all I now need is the
wheel size (actually, the hub center to ground distance would be
better), and the minimum speed at which your exercise machine would be
expected not to flicker.

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.

If that's true, then there may be something wrong with the Shimano
dynamo. Got any electronics test equipment, such as an oscilloscope?
Take a look at the dynamo output with no load and with the light
attached. Measure the frequency at various speeds. There may also be
something wrong with the light, such as having one phase (branch) of
the LED string shorted. Either way, I would expect to see an
asymmetry in the AC waveform which would accentuate any flicker. If
one phase in the light were shorted, then it might be triggering some
kind of protection circuit inside the Shimano hub.

What bothers me is that you say:
"flicker quite noticeably at all speeds".
That's difficult to do when the Shimano hub probably produces a
frequency of 30Hz or greater at operating speeds, which should not be
visible as a flicker. Other than an overcurrent protection circuit
failure in the Shimano hub, I can't imagine how that would be
possible.

Incidentally, if you don't have an oscilloscope, try using a PC and a
sound card:
https://windowsreport.com/oscilloscope-software-pc-laptop/

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

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558