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Old 04-09-18, 10:00 AM   #1
agmetal
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Is there a way to smooth out/reduce low-speed flicker?

A couple of my bikes have the Shimano DH-3N80 hubs with B&M Cyo Premium T headlights, and I find that they have a pronounced low-speed flicker - moreso than another bike with the same headlight and one of the modern Sturmey-Archer dyno/drum brake hubs. Is there any way to reduce this flicker, like for low-speed nighttime climbs?
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Old 04-09-18, 10:16 AM   #2
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You might incur a lot of trouble or expense fixing this. Even if you succeeded, you might not be happy with the brightness, since you'll be taking away from the peaks to fill in the valleys of voltage. I suggest using a battery powered light. If you use it only when your dynamo light flickers, you'll hardly use it at all, and you won't need to charge it often.
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Old 04-09-18, 12:46 PM   #3
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I have one particular ride in mind for this as a potential problem, Boston's "Midnight Marathon" ride this upcoming weekend. Maybe I'll take my USB rechargeable light with me as a backup.
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Old 04-09-18, 01:55 PM   #4
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I know "ride faster" isn't much help, but it's all I got.


Well, mostly. If you can gear down and practice spinning on your climbs, you'll keep your speed more even than kick-n-coast going uphill. That might be enough to even out the power fluctuations.


I find that maintaining 9-10 mph is enough that the fluctuations are minimal.
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Old 04-09-18, 02:37 PM   #5
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I think it would be possible to add a battery to the system, such that in faster parts the excess charge is stored, and in the slower parts the stored charge is used to power the light fully. But I am abysmal with electronics and could not suggest how to do it.
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Old 04-09-18, 02:57 PM   #6
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No, don't put a battery into your dynamo wiring. Bad idea.
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Old 04-09-18, 03:52 PM   #7
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No, don't put a battery into your dynamo wiring. Bad idea.
Explain why, please.
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Old 04-09-18, 04:03 PM   #8
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The dyno wiring is AC, for one thing. Much simpler to just add a battery-powered light that can help you see when going slowly.
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Old 04-09-18, 05:44 PM   #9
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Out of curiosity, what makes it different from this setup from the 1940s and '50s?

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Old 04-10-18, 12:44 PM   #10
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I experience the same thing with an IQ-X and Shimano hub. I will add my vote for a battery light, which I carry as a backup at all times. Suggest a good USB rechargeable model, as they generally hold their charge and no worry about alkaline battery corrosion.
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Old 04-10-18, 07:29 PM   #11
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Why not just appreciate the nice "slow rider" indication it's giving to elderly pedestrians in front of you so they know they don't need to get in any hurry to drag their walkers and oxygen tanks over to the edge of the sidewalk and let you by?
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Old 04-10-18, 08:39 PM   #12
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Why not just appreciate the nice "slow rider" indication it's giving to elderly pedestrians in front of you so they know they don't need to get in any hurry to drag their walkers and oxygen tanks over to the edge of the sidewalk and let you by?
Because they probably wouldn't be walking up steep hills on the road at night?
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Old 04-10-18, 09:42 PM   #13
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Because they probably wouldn't be walking up steep hills on the road at night?
Then why not ditch the greenie toy and get a battery light that doesn't have to misuse units to sound bigger?
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Old 04-11-18, 08:02 AM   #14
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Then why not ditch the greenie toy and get a battery light that doesn't have to misuse units to sound bigger?
I have no idea what you're talking about.

In any case, I haven't ridden in exactly the conditions mentioned with this setup yet, so this might all end up being academic.
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Old 04-11-18, 08:32 AM   #15
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I found that it's only really an issue on super long climbs—once the standlight capacitor is charged, the light flickers less, and has a pretty slow decline to flickering (like 7-8 mph).
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Old 04-11-18, 11:24 AM   #16
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Originally Posted by agmetal View Post
... Is there any way to reduce this flicker, like for low-speed nighttime climbs?

If you are asking if there is a way to modify the B&M light, then the answer is most likely "no". It's very likely that someone could modify the B&M light to do this, but they wouldn't be asking this question on Bike Forums.

If you indeed are able to write code for whatever processor the B&M light might be using, I'd suggest having the processor monitor the dynamo speed via the frequency of the dynamo's AC waveform, and run the LED at a lower current when the AC waveform is below a threshold frequency. This might also require a larger bulk capacitor after the bridge rectifier.

The suggestion to use a battery powered auxiliary light seems like an excellent work-around.

Regarding the side issue of using batteries to store energy to maintain the light's operation during low speed operation.... the downside is that it adds a fair bit of cost to the light, and requires an access panel to permit the eventual replacement of the battery. With a conservative design, I've had NiMH AA cells last for 10 years in one of my standlight designs.
A supercapacitor will last much longer, but is also much more expensive per joule of energy stored, as well as being much larger. I've got one standlight that uses a 100 Farad supercap, which is probably 10 times more expensive than a AA NiMH cell and roughly 4 times larger in volume.

It's possible that someone, somewhere, is making a light that does what you want. Until you find that person, it might be fun for you to write B&M and ask if they would design a light that does what you want. I've heard others ask for the same sort of light, so perhaps there's a market that would be happy to pay the extra cost.


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Old 04-11-18, 03:17 PM   #17
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I found that it's only really an issue on super long climbs—once the standlight capacitor is charged, the light flickers less, and has a pretty slow decline to flickering (like 7-8 mph).
I should check my GPS tracks from the same ride in previous years to see what kind of speeds I was doing on those climbs

Last year, on the most brutal climb, I was averaging about 7-8mph on about an 8% grade, slowing down to 4.5mph for the very end of it. The ride I did over the weekend that got me thinking about this had a climb that was slightly longer, similar grade, but had me noticeably slower. This is definitely, at least in part, a matter of my being out of shape relative to last year, but....

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Old 04-11-18, 03:31 PM   #18
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B&M E-Werk with Pufferakku between Hub and front light.
bumm.de/en/products/stromversorgung/parent/361/produkt/361.html?
bumm.de/en/products/stromversorgung/parent/461/produkt/461a.html?
bikeforums.net/electronics-lighting-gadgets/1122433-busch-mueller-e-werk-configuration.html
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Old 04-11-18, 04:59 PM   #19
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I should check my GPS tracks from the same ride in previous years to see what kind of speeds I was doing on those climbs

Last year, on the most brutal climb, I was averaging about 7-8mph on about an 8% grade, slowing down to 4.5mph for the very end of it. The ride I did over the weekend that got me thinking about this had a climb that was slightly longer, similar grade, but had me noticeably slower. This is definitely, at least in part, a matter of my being out of shape relative to last year, but....
Bear in mind, my longest sustained climb around here is something like 1 mile long, so my results may very well differ from yours.
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Old 04-11-18, 07:25 PM   #20
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I have no idea what you're talking about.
1 Lux = 1 lumen/square meter. It's meaningless without a properly defined measurement condition.

The only meaning that could possibly make sense without more definition would be the lumen output per square meter of the emitter itself, but then 80Lux over roughly .001 square meter would be .08 lumens, or about as bright as a bit of glow in the dark paint. Hence they can claim pretty much any number they want and then redefine the testing conditions to make it fit.
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Old 04-11-18, 09:46 PM   #21
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Originally Posted by KD5NRH View Post
1 Lux = 1 lumen/square meter. It's meaningless without a properly defined measurement condition.

The only meaning that could possibly make sense without more definition would be the lumen output per square meter of the emitter itself, but then 80Lux over roughly .001 square meter would be .08 lumens, or about as bright as a bit of glow in the dark paint. Hence they can claim pretty much any number they want and then redefine the testing conditions to make it fit.
I take it that you've never used one of these lights, then. I find them more than sufficient to see where I'm going on an unlit road or path at night. The issue is that at walking pace, and potentially at climbing-up-a-brutal-hill pace, the light has a noticeable flicker, which is a bit annoying.

Also, don't forget that the lights are made to be compliant with Germany's StVZO requirements for bicycle lighting, so....
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Old 04-11-18, 10:22 PM   #22
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That's really wierd, I have a shimano alfine hub with a b&m cyo (an older model) and there's almost no flicker. Just a bit at walking speed.

I actually bought a schmidt light and was a bit shocked that it had significant flicker at walking speed, whereas my cyo just was mild barely-even-notice-it stuff.

I don't know how you could fix it after you've bought the stuff though, it seems to be an attribute of the electronics used.
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Old 04-12-18, 12:11 AM   #23
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I take it that you've never used one of these lights, then.
Translation: "DON'T YOU TELL ME NO SCIENCE!!! MAH FEELZ TELL ME THEY GOOD!!!"
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Old 04-12-18, 01:37 AM   #24
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Originally Posted by steelbikeguy View Post
If you are asking if there is a way to modify the B&M light, then the answer is most likely "no". It's very likely that someone could modify the B&M light to do this, but they wouldn't be asking this question on Bike Forums.

If you indeed are able to write code for whatever processor the B&M light might be using, I'd suggest having the processor monitor the dynamo speed via the frequency of the dynamo's AC waveform, and run the LED at a lower current when the AC waveform is below a threshold frequency. This might also require a larger bulk capacitor after the bridge rectifier.

The suggestion to use a battery powered auxiliary light seems like an excellent work-around.

Regarding the side issue of using batteries to store energy to maintain the light's operation during low speed operation.... the downside is that it adds a fair bit of cost to the light, and requires an access panel to permit the eventual replacement of the battery. With a conservative design, I've had NiMH AA cells last for 10 years in one of my standlight designs.
A supercapacitor will last much longer, but is also much more expensive per joule of energy stored, as well as being much larger. I've got one standlight that uses a 100 Farad supercap, which is probably 10 times more expensive than a AA NiMH cell and roughly 4 times larger in volume.

It's possible that someone, somewhere, is making a light that does what you want. Until you find that person, it might be fun for you to write B&M and ask if they would design a light that does what you want. I've heard others ask for the same sort of light, so perhaps there's a market that would be happy to pay the extra cost.


Steve in Peoria
It should be easy enough to build a box with a bridge rectifier and capacitor to reduce ripple to be placed between the generator and the headlamp.

The headlamp shouldn't care whether it is AC or DC power feeding it. Is the bulb incandescent or LED? If it is incandescent, then replace with a LED bulb at the same time.

Once one has DC, then it should be possible to add a backup battery, although the "super capacitor" might be a more durable option.
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Old 04-12-18, 01:54 AM   #25
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Originally Posted by KD5NRH View Post
1 Lux = 1 lumen/square meter. It's meaningless without a properly defined measurement condition.
Measurement takes place in 10m distance. It's all specified around the StVZO-regulations.


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That's really wierd, I have a shimano alfine hub with a b&m cyo (an older model) and there's almost no flicker. Just a bit at walking speed.
I actually bought a schmidt light and was a bit shocked that it had significant flicker at walking speed, whereas my cyo just was mild barely-even-notice-it stuff.
I don't know how you could fix it after you've bought the stuff though, it seems to be an attribute of the electronics used.
The reason is the higer wattage of the lights. As brighter they get, as more power do they need. At low speeds the power of the dynamo isn't high enough, so it's a typical AC problem.
Lights with <60lx have less wattage and so the delivered current at low speeds can be sufficent.

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