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#11
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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 |
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#13
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Dynamo/LED power conditioning
On Wednesday, May 2, 2018 at 9:49:23 PM UTC-5, 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. bob prohaska I have this dynamo hub. http://www.starbike.com/p/Shimano-dy...er-36H-5206-en And two(2) of these lights hooked to the dynamo. http://www.starbike.com/en/busch-and...umotec-iq-cyo/ I can ride at any speed, 4-5 mph or greater, and have good lighting without any flickering. So I'd say something is wrong with either the hub or lights you are using. |
#14
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Dynamo/LED power conditioning
On Thursday, May 3, 2018 at 3:49:23 AM UTC+1, 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. bob prohaska Bob, it looks like you're trying to make more light than the dynamo can provide current for: that's just too many diode drops, so try fewer LEDs. I have had my doubts about Busch und Muller lamps in the past, and also the bullying marketing tactics of their fans, but their current Cyo lamp is perfectly adequate, and leaves enough power for the rear lamp. It's probably cheaper than anything as good that you can build, and it has roadable optics with a car-friendly cutoff, a standlight and auto-switching. Sorting that lot out from their circuit, which is full of unknown and unmarked components, will theoretically leave you with the information you want. But how to eliminate what you don't want is the problem. My experience is that Shimano dynamos, of which the -72 was once the most desirable model, come up to maximum output faster than SON dynamos, that is, provide a steady, useful light at lower speed. So if you see flickering at low speed with a Shimano hub dynamo, you're overloading it. AJ |
#15
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Dynamo/LED power conditioning
Sepp Ruf wrote:
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 : 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. The classic B&M circuits used rectification and current-doubling to fully power one 1 amp led. Your 2x3S LED approach is quite different. http://candlepowerforums.com/vb/showthread.php?430445 Good luck! Simpler: http://www.pilom.com/BicycleElectronics/DynamoCircuits.htm :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. https://www.mtb-news.de/forum/t/nabendynamo-mosfet-mc-e-flackert-wie-wild.676394/ This is the sort of thing I was looking for, thank you! bob prohaska |
#16
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Dynamo/LED power conditioning
Ralph Barone wrote:
Three white LEDs in series probably needs nearly 10-12 V just to overcome the diode drop. Try just two in series and see if that helps things. Yes, it might help a little. It turns out (after a short night ride) that the flicker is most apparent only to someone looking directly at the LEDs, which operate on alternate half-cycles. An observer seeing the illuminated field notices much less flicker, though it never goes away at any speed I can maintain. Given the complexity of the circuits described in the links Sepp posted I am very tempted to try living with what I've got. A MOSFET bridge and peaking capacitor seem like a decent next step if the flicker causes serious trouble. Thanks for writing! bob prohaska |
#17
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Dynamo/LED power conditioning
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#18
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Dynamo/LED power conditioning
On 5/4/2018 12:06 AM, bob prohaska wrote:
I'm unaware of any well-made, modern sidewall generators for bicycles. For many years I used an old Soubitez roller dynamo, replacing it only after plastic mounting parts started cracking. In performance terms I think it's better than a hub dynamo (less weight, better output, acceptable drag) but they are no longer in production and scarce on Ebay. The one bottle dynamo I tried got hot to the touch at 10 mph. I'm curious, what make of dynamo got hot at 10 mph? I have ancient Union bottles on two bikes. I don't recall them ever getting beyond very slightly warm - I'd guess maybe 90 degrees Fahrenheit. This place has bottle dynamos: https://www.sjscycles.co.uk/dynamos-bottle/ I've bought other stuff from them. Price and shipping speed seem very competitive with American sources, and selection tends to be much better. If I get a B&M headlight, it'll probably go on my UpTown 8 grocery chaser. It's hard to find bulbs for the halogen front light, and that bike is at least occasionally ridden in earnest at night. This place has been a good source for bulbs of all kinds: http://www.reflectalite.com/ They also have LEDs that are drop-in replacements for halogen dyno bulbs. I bought one for a friend and have another in a headlamp that I've only bench tested in my basement. It seems very good, but I haven't tried it on the road. It's not yet needed on any of my bikes. -- - Frank Krygowski |
#19
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Dynamo/LED power conditioning
Jeff Liebermann wrote:
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. Alas, no test equipment beyond a cheap DVM with 400mA AC current range. I get 28 "notches" per turn on the hub, in a 27" wheel. Current reaches 400 mA at a modest speed, probably 10 mph. Voltage (which I can't measure simultaneously) reaches 10.3 V at a similar speed and won't exceed 10.5 V with any effort I can realistically exert. There is of course no guarantee the meter is true RMS and the wafeforms are not sinusoidal, but the numbers suggest nothing radically wrong with either the hub or the LEDs (all six look about the same). 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/ There's an audio signal processing app for iPads that can do something crudely similar. It's not an oscilloscope, per se, but does give a waveform display. If the puzzle gets deeper it might be worth trying. At the moment I see no reason to suspect malfunction, either in the dynamo or the LEDs. Part of the issue can be seen in a darkened garage: Spinning the front wheel casts double shadows from the two sets of LEDs. Without the shadow effect the scene looks much less strange. With a shadow, or looking directly at the LEDs, it's quite conspicuous. I suspect the lateral "movement" is what catches the eye. The roller dynamo has 8 poles and runs at roughly 20 times wheel speed. Even with 28 poles the frequency of the hub dynamo is roughly 6x lower than the roller setup, which seems enough to account for the flicker, especially when combined with the alternating groups of LEDs. It looks like the only defect is my failure to consider the lower operating frequency of the hub dynamo. Now the question is what, if anything, to do about it. Thanks to everybody who replied, this has been a most informative discussion! bob prohaska |
#20
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Dynamo/LED power conditioning
Andre Jute wrote:
My experience is that Shimano dynamos, of which the -72 was once the most desirable model, come up to maximum output faster than SON dynamos, that is, provide a steady, useful light at lower speed. So if you see flickering at low speed with a Shimano hub dynamo, you're overloading it. I believe you've hit the nail on the thumb 8-) A DPST switch wired to shunt one LED in each branch is probably the simplest fix. That'll give better light at low speed. The flicker is useful during the day and tolerable over about 10 mph at night. Thank you for writing! bob prohaska |
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