Hub dynamo on tire
11-21-24 | 11:58 AM
#26
Randomhead
Joined: Aug 2008
Posts: 25,930
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From: Happy Valley, Pennsylvania
All Tourist's chart tells me is that I really need to start using my SoN Delux instead of the Shimanos I am currently using. Change is hard. I also need to build a fork and get it painted.
I guess my SP hubs aren't so bad, but they are all on gravel or off-road wheels.
I guess my SP hubs aren't so bad, but they are all on gravel or off-road wheels.
11-21-24 | 02:34 PM
#27
Senior Member
Joined: Aug 2010
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From: Madison, WI
Bikes: 1961 Ideor, 1966 Perfekt 3 Speed AB Hub, 1994 Bridgestone MB-6, 2006 Airnimal Joey, 2009 Thorn Sherpa, 2013 Thorn Nomad MkII, 2015 VO Pass Hunter, 2017 Lynskey Backroad, 2017 Raleigh Gran Prix, 1980s Bianchi Mixte on a trainer. Others are now gone.
What surprised me the most on those two graphs was that the drag was roughly double the electrical output.
That said, I often ride with my lights on in daytime, I know the drag is there but I can't feel it. Exception, when bike touring I am usually using my dynohub to charge batteries. Fortunately the dyno powered USB chargers are much more efficient than the hubs.
That said, I often ride with my lights on in daytime, I know the drag is there but I can't feel it. Exception, when bike touring I am usually using my dynohub to charge batteries. Fortunately the dyno powered USB chargers are much more efficient than the hubs.
11-21-24 | 06:01 PM
#28
Randomhead
Joined: Aug 2008
Posts: 25,930
Likes: 4,825
From: Happy Valley, Pennsylvania
With the shimano hubs, the drag is more than double. And also, the output is lower. I sorta lost track of how bad they are. I'm glad they didn't measure the hubs I have on my commuter.
11-22-24 | 08:47 AM
#29
aka Tom Reingold
Joined: Jan 2009
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From: New York, NY, and High Falls, NY, USA
Bikes: 1962 Rudge Sports, 1971 Raleigh Super Course, 1971 Raleigh Pro Track, 1974 Raleigh International, 1975 Viscount Fixie, 1982 McLean, 1996 Lemond (Ti), 2002 Burley Zydeco tandem
I ride with my lights on all the time. Maybe the drag slows me down. I don't feel it. The light may not make me safer, but it still seems worthwhile.
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Tom Reingold, tom@noglider.com
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Tom Reingold, tom@noglider.com
New York City and High Falls, NY
Blogs: The Experienced Cyclist; noglider's ride blog
“When man invented the bicycle he reached the peak of his attainments.” — Elizabeth West, US author
Please email me rather than PM'ing me. Thanks.
11-22-24 | 09:29 AM
#30
Randomhead
Joined: Aug 2008
Posts: 25,930
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From: Happy Valley, Pennsylvania
It's not at all important on short rides. Over a 10 hour or longer ride, it may not be noticeable but 10w is 5% of my endurance power. Increasing my ftp by the difference between a Shimano and a SoN would be nice.
11-27-24 | 03:17 PM
#31
Dynamo tech expert
Joined: Oct 2024
Posts: 60
Likes: 2
I've measured 100v open-circuit on my SON28.. but it was at 50mph. There's nothing quite as fun as riding down a steep hill at 50mph and trying to read the multi-meter rubber-banded to your handlebars! 
I'm going to guess that someone in Germany knows what fails first when trying to maximize output power at high speeds. Maybe the copper wire gets warm enough to produce shorts in the enamel insulation? There is probably some hysteretic core loss at high speed that would contribute to heating the wire.
As for open-circuit voltage... the headlight circuit design would determine how sensitive it is to high voltage. I took apart a dead B&M Lumotec Eyc for fun. It uses a little momentary switch to control the function, so some internal circuitry is always powered up. It has a bidirectional protection zener at the dynamo input. It appears to be a 100V transorb. That would make you think the circuitry is rated to handle 100V, but the transorb is located at the input to the full wave bridge rectifier, and at the output of the bridge rectifier is a 680uF, 10V cap. I'm not sure what the transorb is protecting if that cap is only rated for 10V. I can't decide whether there is enough current draw by the Eyc to keep the dynamo voltage pulled down to a low, safe level, ... or whether B&M assumes that no one is going very fast.
I think the question about whether open-circuit voltage matters will end up being the standard engineering answer.... "it depends".
Steve in Peoria
I'm going to guess that someone in Germany knows what fails first when trying to maximize output power at high speeds. Maybe the copper wire gets warm enough to produce shorts in the enamel insulation? There is probably some hysteretic core loss at high speed that would contribute to heating the wire.
As for open-circuit voltage... the headlight circuit design would determine how sensitive it is to high voltage. I took apart a dead B&M Lumotec Eyc for fun. It uses a little momentary switch to control the function, so some internal circuitry is always powered up. It has a bidirectional protection zener at the dynamo input. It appears to be a 100V transorb. That would make you think the circuitry is rated to handle 100V, but the transorb is located at the input to the full wave bridge rectifier, and at the output of the bridge rectifier is a 680uF, 10V cap. I'm not sure what the transorb is protecting if that cap is only rated for 10V. I can't decide whether there is enough current draw by the Eyc to keep the dynamo voltage pulled down to a low, safe level, ... or whether B&M assumes that no one is going very fast.
I think the question about whether open-circuit voltage matters will end up being the standard engineering answer.... "it depends".
Steve in Peoria
11-27-24 | 07:35 PM
#32
Senior Member
Joined: Feb 2008
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From: Peoria, IL
The transorb will be for spikes not over-voltage protection. The LED in that light isn't enough to keep the voltage below 10V, are you sure there isn't something after the rectifier doing over-voltage protection? I would expect a 10V cap to go to 6V, which incidentally is what Son Edelux 2 keeps it at. It makes me think there's another piece.
The rest is just a little microcontroller, an inductor to buck the voltage down for the LED(s), and a ton of small transistors or diodes.
My best guess at this time is that the light must use the "daytime running light" LEDs as a way pull down the dynamo voltage to a level that is safe for the 10V cap.
I was given this light because it's dead. It's entirely possible that it isn't designed to tolerate a dynamo run at high speed.
I haven't figured out why it's dead, so any guess about the cause of death is reasonable. No components blown up, though.
Pics attached below...
Steve in Peoria
11-28-24 | 02:53 AM
#33
Dynamo tech expert
Joined: Oct 2024
Posts: 60
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The daytime running lights wouldn't be enough, unlikely would the main light on a faster descent.
Is the DC going through what looks like a PTC at the top edge? A zener somewhere else keeps the voltage down and the PTC heats up as it starts doing so which saves the zener from destruction. Efficiency is poor during normal use but for the relatively low light output and price point it would be acceptable.
Is the DC going through what looks like a PTC at the top edge? A zener somewhere else keeps the voltage down and the PTC heats up as it starts doing so which saves the zener from destruction. Efficiency is poor during normal use but for the relatively low light output and price point it would be acceptable.
11-28-24 | 11:43 AM
#34
Senior Member
Joined: Feb 2008
Posts: 5,309
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From: Peoria, IL
The daytime running lights wouldn't be enough, unlikely would the main light on a faster descent.
Is the DC going through what looks like a PTC at the top edge? A zener somewhere else keeps the voltage down and the PTC heats up as it starts doing so which saves the zener from destruction. Efficiency is poor during normal use but for the relatively low light output and price point it would be acceptable.
Is the DC going through what looks like a PTC at the top edge? A zener somewhere else keeps the voltage down and the PTC heats up as it starts doing so which saves the zener from destruction. Efficiency is poor during normal use but for the relatively low light output and price point it would be acceptable.
Here's a version of the photo where I labeled the parts that I'd identified so far (which isn't much)...
I added these labels before learning that the protection diode was a TVS.
For what's it's worth, here is a shot of the diode when I was trying to get it to conduct (which I didn't, because I don't have a power supply that goes high enough).
as best as I could tell, the markings are:
1st line: ST @G (not sure about the @ symbol)
2nd line: NY
3rd line: Z537
a buddy was able to look up the markings and concluded that it is a ST SM6T100CA.
This is a 100V bidirectional transorb in a SMB package.
Steve in Peoria
11-28-24 | 12:11 PM
#35
Dynamo tech expert
Joined: Oct 2024
Posts: 60
Likes: 2
I missed a picture earlier, it's just a 22 ohm resistor.
You may find the three components to the side of the diodes are acting as a crowbar. It looks one could be a zener and one an SCR.
If there isn't a means to stop the backflow from the capacitor it might be sinking too much current through the SCR, although that being said the capacitor is small so won't be able to sink a large current. If there isn't a means to stop the backflow that likely resets what looks like a buck converter (not a CPU), but since LED's are so slow it wouldn't be user visible.
You may find the three components to the side of the diodes are acting as a crowbar. It looks one could be a zener and one an SCR.
If there isn't a means to stop the backflow from the capacitor it might be sinking too much current through the SCR, although that being said the capacitor is small so won't be able to sink a large current. If there isn't a means to stop the backflow that likely resets what looks like a buck converter (not a CPU), but since LED's are so slow it wouldn't be user visible.
