Author Topic: Best hub generator front lamp for avoiding low speed flicker?  (Read 1491 times)

Best hub generator front lamp for avoiding low speed flicker?
« on: February 18, 2019, 01:58:26 pm »
It seems my Herrmans H One S does flicker annying when powered from a hub generator at low speed:

are there any front lamps that avoid this?

Do German epileptics not complain? (it seemed much more objectionable than a filament bulb lamp (on which Stzvo hub dyno frequency vs speed rule is based): I do not understand why Stzvo do not insist manufacturers design their lamps properly to avoid this problem.

Any neat electronic solutions to fit between lamps and hub?



 

Re: Best hub generator front lamp for avoiding low speed flicker?
« Reply #1 on: February 18, 2019, 03:08:13 pm »
My tourer has a Schmidt SON generator hub and an E-delux light. No flicker whatsoever, and the standlight starts working very soon after I start wheeling the bike out of the bike storage room at work. My winter/snow bike has a Shimano generator and Busch & Mueller LED headlight. It flickers noticeably at low speed, and the standlight takes noticeably longer to start working properly. I suspect that the difference lies in the design of the hub generator.

Cudzoziemiec

  • Solar powered, tea fuelled cycle-wol
Re: Best hub generator front lamp for avoiding low speed flicker?
« Reply #2 on: February 18, 2019, 05:15:16 pm »
A guy who rides with the local CTC has an SP headlight. I'm not sure what generator he has, presumably also an SP. It is the most flickery thing I've ever seen. It prompts one or two in the group to complain about flashing headlights (one in particular tends to love complaining about that sort of thing). Eventually he fitted a homemade smoothing device he mantled out of a capacitor and bits in a huge ugly black plastic box to smooth it. Before he did that it was far worse than any other headlight I've ever seen off an SP, so in addition to this being a warning to stay clear of SP lights, I'd say it probably depends more or as much on the light as the generator. SP dynamos in general are very good.
An ungovernable laughter, a joyous agitation which makes the summer stretching before you seem like an unrolling canvas on which you might draw those first rude pure strokes that are free. (Capote)

Kim

  • Timelord
Re: Best hub generator front lamp for avoiding low speed flicker?
« Reply #3 on: February 18, 2019, 05:49:41 pm »
It's going to be the lamp (specifically, how much smoothing and regulation is performed after rectification) rather than the generator (they're all going to be outputting something more or less sinusoidal).  Smoothing means storing energy in capacitors or batteries, which are bulky, relatively expensive and prone to failure, so it's a prime candidate for economising at the design stage.  I can imagine half-wave rectification (either through failure or design) exacerbating the flicker, by effectively halving the frequency.  Also the dynamo-for-small-wheels-in-a-full-sized-wheel-to-save-weigh/drag trick will increase low-speed flicker (conversely, a dynamo for full-sized wheels built into a small wheel will reduce it).

I suppose you could do something neat with thyristors (think classic TRIAC dimmer circuit) to keep the light off until the generator is up to speed.  I'd generally prefer flickering light to no light, though, especially in traffic.  Feeding dynamo lights DC from a battery isn't always a good idea.

Honourable mention to the B&M 4DToplight Multi: Its 'standlight' is powered by a pair of AA batteries, which is a lot less inconvenient than it sounds, because since they're only used when the bike isn't in motion they last approximately forever.  I can see an argument for a front light equivalent aimed at slow climbers, but I've never seen such a product.

How does the Luxos U (or other lights with a buffer battery for USB charging) behave at low speed?
To ride the Windcheetah, first, you must embrace the cantilever...

Re: Best hub generator front lamp for avoiding low speed flicker?
« Reply #4 on: February 18, 2019, 06:15:38 pm »
How does the Luxos U (or other lights with a buffer battery for USB charging) behave at low speed?

If the battery is charged, it stays on at full normal power, no flickering. When I had one on my Brompton it had the nice trick that when unfolding the tiny movement of the front wheel was enough to flick it on, which gave the impression of having clever automatic lights.

If only they'd thought about making it even slightly waterproof.

Kim

  • Timelord
Re: Best hub generator front lamp for avoiding low speed flicker?
« Reply #5 on: February 18, 2019, 06:20:51 pm »
How does the Luxos U (or other lights with a buffer battery for USB charging) behave at low speed?

If the battery is charged, it stays on at full normal power, no flickering. When I had one on my Brompton it had the nice trick that when unfolding the tiny movement of the front wheel was enough to flick it on, which gave the impression of having clever automatic lights.

I fitted my Brompton rear light with a tilt switch and low-value resistor to discharge the standlight capacitor when you flip the rear wheel under.  This was mostly about having a way to turn it off quickly (for railway platforms) without compromising the waterproofing, but clever automatic lights are always nice :)


Quote
If only they'd thought about making it even slightly waterproof.

Indeed...
To ride the Windcheetah, first, you must embrace the cantilever...

Re: Best hub generator front lamp for avoiding low speed flicker?
« Reply #6 on: February 18, 2019, 08:27:55 pm »
It's going to be the lamp (specifically, how much smoothing and regulation is performed after rectification) rather than the generator (they're all going to be outputting something more or less sinusoidal).  Smoothing means storing energy in capacitors or batteries, which are bulky, relatively expensive and prone to failure, so it's a prime candidate for economising at the design stage.
Yes. I extracted the circuit from my old unused Basta Pilot Steady LED front:
Its just a rectifier (preceded by some backtoback (presumably highish voltage zeners to protect it) followed by 0.66Farad of standlicht caps (protected by a presumably 5.1V of paralleled zeners (with no dropper resistor: ie clamps overall dynamo voltage to 2Vrectifierdiode + 5.1 ==  6.5V peak rather than the 8v5 peak corresponding to 6Vrms), with led driven via a 3.9R resistor (ie > 350mA). It flickers annoyingly. I suppose cheap super caps mightnt charge fast enough for smoothing, but my attempts to prevent warble in a reflectalite LED bulb powered by bottle generator thru just a bridge rectifier where made worse by large smoothing capacitor (10 or 20000uF).
Isn't the problem going to be that: load LED circuit  sees smoothing cap charged to peak of dynamo voltage, draws current appropriate for that and empties cap before next half-cycle starts: ie at low speed led current needs to be kept lower so as LED is lit over whole half cycle?.
I found this https://www.ebay.co.uk/itm/16V1F-2F-Farad-Capacitor-Module-2-7V-10F-Super-Capacitor-With-Protection-Board/232879025831?hash=item3638abeea7:g:m2YAAOSwTDNbar4f:rk:1:pf:0
Quote from: Kim
....I suppose you could do something neat with thyristors ... to keep the light off until the generator is up to speed...
I want some light at low speed too :) , so...
Quote
..  Feeding dynamo lights DC from a battery isn't always a good idea.
Which is what I think Stzvo got wrong: LED dynamo lights are meant to be a drop in replacement for filament ones which work of DC quite happily,  thus IMHO  Stzvo should require that a dynamo hub front lamp must either work perfectly well from 6V AC or DC, or alternatively have a DC input (eg mini shimano style connector from which it (and any slaved rear lamp may be powered).
Quote from: Kim
Honourable mention to the B&M 4DToplight Multi: Its 'standlight' is powered by a pair of AA....I can see an argument for a front light equivalent aimed at slow climbers, but I've never seen such a product.
I prefer no batteries INside dynamo lamps but as mentioned above a DC in connector (Shimano-Style spades) on the front lamp would seem OK. Also, rear lamps seem less annoying and I prefer line style lamps, but I was hoping given that hub rear lamps are usually slaved to the front, fixing the front flicker fixes the rear warble :)
Quote from: Kim
...  I can imagine half-wave rectification (either through failure or design) exacerbating the flicker, by effectively halving the frequency.
Arggh, surely not in high/medium end designs,  :( . Even the PIco 30 seems to have a bridge https://forum.cyclinguk.org/viewtopic.php?t=120923&start=105#p1307428.
Quote
Also the dynamo-for-small-wheels-in-a-full-sized-wheel-to-save-weigh/drag tri will increase low-speed flicker (
Unfortunately it is a 26in wheel with matching generator :(

Some cheaper (ie low power) Axa front lamps are marked as 6V E bike compatible, similarly rear lamps: but not the higher power ones (which I want eg Axendo 60) it seems....

Re: Best hub generator front lamp for avoiding low speed flicker?
« Reply #7 on: February 18, 2019, 08:51:23 pm »
possibly charging a smoothing cap via a diode and discharging it through a low value resistor may reduce flicker?

cheers

Re: Best hub generator front lamp for avoiding low speed flicker?
« Reply #8 on: February 19, 2019, 08:19:12 pm »
What counts as slow speed? 3mph I can't help you with, 5mph upwards we ought to be able to do something.

Oddly a cheaper capacitor should help with flickering, since it's dynamic response usually isn't as rapid. A bigger capacitor will also help, since it will be a bigger sponge to absorb and release energy from.

I have a 3 of these split between the homebrew rear lights on my bike: https://cpc.farnell.com/panasonic-electronic-components/eecf5r5u155/capacitor-1-5f-5-5v/dp/CA06062. Anything above walking pace and the lights are pretty solid. Time to full brightness isn't that big, 10 yards tops, and then it's just a case of the first 30 seconds of movement get them fully charged. I don't have clever discharge circuitry, so it's a linear decline, but over 5 minutes or so until not really useful, and 10 minutes on the single LED until all gone.
Cruzbike V2k

Re: Best hub generator front lamp for avoiding low speed flicker?
« Reply #9 on: February 19, 2019, 08:23:33 pm »
I have a 3 of these split between the homebrew rear lights on my bike: https://cpc.farnell.com/panasonic-electronic-components/eecf5r5u155/capacitor-1-5f-5-5v/dp/CA06062. Anything above walking pace and the lights are pretty solid. Time to full brightness isn't that big, 10 yards tops, and then it's just a case of the first 30 seconds of movement get them fully charged....
Thanks, I suspect the front lamp is more problematic due to using most of the hubs output compared to rear lamp.

Re: Best hub generator front lamp for avoiding low speed flicker?
« Reply #10 on: February 19, 2019, 08:28:53 pm »
possibly charging a smoothing cap via a diode and discharging it through a low value resistor may reduce flicker?
I should have mentioned that I do wish to modify the internals of the lamp (in order to keep its 'approved-ed-ness', except perhaps to wire a battery across the Standlicht caps: unfortunately the cheap lamps like pico (and pilot) seem to think they can clamp the voltage of the system to less than the normal dynamo voltage, which annoys me, and makes such a mod less attractive to me-- what if it the unnecessary voltage depression reduces the brightness of the rear lamp etc, and its wasting power/voltage I might want.....

Thus  I would prefer an external solution (or a lamp where the manufacturer has done the work for me...): 
what about a solid state (bidirectional MOSFET relay) used to pulse-width modulate the hub sine wave so that it appears less peaky: ie narrower pulses at sine peak, widening toward the sine half cycle's start and end.  Presumably tricky (I suspect would cause most to reach for a microcontroller?).
A front lamp that could stand DC would allow the old-school batterry backup solution of  relay, perhaps with rectifier mixer to save battery power....

Didn't the dynamo Solidlights use fancy microcontroller-ness to avoid flicker?


Re: Best hub generator front lamp for avoiding low speed flicker?
« Reply #11 on: February 19, 2019, 11:49:30 pm »
You are embarking on a 'project'. I built LED lights when commercial models were not available, and very good they were with little flicker. Now I can buy a several good type approved lamps it's just not worth the bother. The IQ-x is my preference.
If you still want to do your own thing. Rectify using Shottky diodes, Voltage limit using an SCR shunt. Fill a fat capacitor and then design a regulator that will hold on at low voltages but as speed rises soft start.. never drawing more than 500mA AC from the  generator(alternator). All LEDs are DC so adding a battery as with the Toplight rear would be trivial after all that design and development work.

Kim

  • Timelord
Re: Best hub generator front lamp for avoiding low speed flicker?
« Reply #12 on: February 19, 2019, 11:51:58 pm »
If you still do need some guidance rectify using shottky diodes, voltage limit using an SCR fill a fat capacitor and then design a regulator that will hold on at low voltages and but soft start.. never drawing more than 500mA from the  Alternator.

...and once the easy bit's out of the way, you can start work on the optics and a waterproof enclosure.

(Actually, given what's mentioned upthread, perhaps improving the enclosure of a Luxos U wouldn't be a bad approach...)
To ride the Windcheetah, first, you must embrace the cantilever...

Re: Best hub generator front lamp for avoiding low speed flicker?
« Reply #13 on: February 20, 2019, 12:02:40 am »
I used to have  fun makin' stuff. Even a motor driven wheel, think rolling road for testing. But #1 to wot Kim sez.

Re: Best hub generator front lamp for avoiding low speed flicker?
« Reply #14 on: February 20, 2019, 01:25:45 pm »
Honourable mention to the B&M 4DToplight Multi: Its 'standlight' is powered by a pair of AA batteries, which is a lot less inconvenient than it sounds, because since they're only used when the bike isn't in motion they last approximately forever.  I can see an argument for a front light equivalent aimed at slow climbers, but I've never seen such a product.
I did have, at one stage in the distant past, a Byka Owl, which was dynamo + 4xAA. IIRC, there were 2 models - basic, which just switched over to AA when below the speed threshold, and advanced, which would also charge the AAs if you were going fast.
https://forum.cyclinguk.org/viewtopic.php?t=91270&start=45#p831658

Cudzoziemiec

  • Solar powered, tea fuelled cycle-wol
Re: Best hub generator front lamp for avoiding low speed flicker?
« Reply #15 on: February 20, 2019, 01:49:37 pm »
I remember the name Byka (though not Owl) but I never had one and didn't know that was how it operated.
An ungovernable laughter, a joyous agitation which makes the summer stretching before you seem like an unrolling canvas on which you might draw those first rude pure strokes that are free. (Capote)

Re: Best hub generator front lamp for avoiding low speed flicker?
« Reply #16 on: February 20, 2019, 09:50:15 pm »
If you still do need some guidance rectify using shottky diodes, voltage limit using an SCR fill a fat capacitor and then design a regulator that will hold on at low voltages and but soft start.. never drawing more than 500mA from the  Alternator.

...and once the easy bit's out of the way, you can start work on the optics and a waterproof enclosure.

(Actually, given what's mentioned upthread, perhaps improving the enclosure of a Luxos U wouldn't be a bad approach...)

Is that the point at which a 3D scanner, 3D printer and a bit of talent with the CAD (more CAO is what it would be in french, don't know what computer aided design conception is in english) would be handy? Pity that my talents don't stretch that far  ???

Re: Best hub generator front lamp for avoiding low speed flicker?
« Reply #17 on: February 21, 2019, 01:00:52 pm »
ISTR that there is a trend away from smoothing capacitors in LED lights because they reduce efficiency.  Lights are sold on lux (or lumens), not on flicker.
Never tell me the odds.

Re: Best hub generator front lamp for avoiding low speed flicker?
« Reply #18 on: February 21, 2019, 11:05:32 pm »
No need for me to design optics because my need for an approved lamp means I just either want a lamp with enough electrikery to avoid flashing or to make an external box of such electronictrickery to place between hub and lamp:---

...Fill a fat capacitor and then design a regulator that will hold on at low voltages but as speed rises soft start.....
That reminds me of the backup circuit described in Dec 94 of Electronics World (and related letter in Oct 95 correcting that the works 'up to 15kmh' had been mistakenly added:
It was a series voltage doubler(Greinacher circuit) followed by 26.8Volts of Zener clamp, followed by a step down regulator, which was not enabled till approx 20V was reached (IMO), thus soft start. The backup was charged, the designer claimed the higher voltage operation provided extra efficiency to compensate for the rectifier and step down losses.

I wonder if one could just leave out the step down section and run Stzvo E bikelights rather dyno ones....

Re: Best hub generator front lamp for avoiding low speed flicker?
« Reply #19 on: February 22, 2019, 10:01:02 pm »
A lumpy trike ride with tired legs has got me speculating about what exactly our  OP is describing as 'flicker' My IQx has no low speed flicker but a pushy pedalling style on hills will intensity  modulate the light. A trike is a useful test as you can ride very slowly!

Re: Best hub generator front lamp for avoiding low speed flicker?
« Reply #20 on: February 23, 2019, 12:40:58 pm »
... me speculating about what exactly our  OP is describing as 'flicker' ....
Find somewhere with lots of hire scheme bikes, eg Belfast Bikes, with hub dynamos and cheap Pico front lamps or similar, when many riders will ride or wheel bikes toward you slowly:
At low speed the front lamps will strobe you with bright flashes as the LED empties the smoothing cap early then remains off over remainder of waveform half-cycle till cap charge up a bit then again...... 

Re: Best hub generator front lamp for avoiding low speed flicker?
« Reply #21 on: February 23, 2019, 06:00:43 pm »
' My IQx has no low speed flicker

My IQx with SON on the tandem is very flickery at 5-6mph and below.  It may be modulation but the effect is flicker.  TBH I'm not very happy about it.

DaveJ

  • Happy days
Re: Best hub generator front lamp for avoiding low speed flicker?
« Reply #22 on: February 23, 2019, 10:15:18 pm »
I've got a Edeluxe II on a SON and that flickers annoyingly at slowish speeds.  The SON originally ran a Solidlights and that combination didn't flicker at a similar speed.  Both the SON and the Edeluxe have been back to Schmidt separately (via SJS) and apparently they are both OK.  I too am quite disappointed.

I have a cheapo Shimano dynohub running a Cyo IQ Premium, and that seems brighter, and less flicker at low speed, so I wonder if someone at Schmidt didn't check something properly.

 


Kim

  • Timelord
Re: Best hub generator front lamp for avoiding low speed flicker?
« Reply #23 on: February 23, 2019, 10:18:18 pm »
The Cyos seem to be abnormally good in their lack of low-speed flicker.  My Cyo R and Cyo Premium are certainly less flickery than either the IQ-X or low-end lights like the Lyt or that Basta one that was popular a few years ago.
To ride the Windcheetah, first, you must embrace the cantilever...

Re: Best hub generator front lamp for avoiding low speed flicker?
« Reply #24 on: February 28, 2019, 12:13:23 pm »
The Cyos seem to be abnormally good in their lack of low-speed flicker...
Is that on a 26 or 700c wheel (rather than a little one?)

It seems I have unfairly impugned the H One S V2:
I was prompted to retest it* and its seems to accept -ve DC (wrt 'ground-y' labeled input spade)... I wonder what sort of rectifier circuit would cause that--- its surely to powerful to use a half wave rectifier: perhaps a mosfet bridge followed by a diode before smoothing cap (but why -ve? upside down circuits give me a headache ).

*I remember thinking I had trying both polaritys so I must have inadvertently swapped back again :(