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Old 10-10-11, 03:55 PM   #1
pwdeegan
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MTBiking with a dynamo light

I've seen references to people doing this, but what are thoughts in this forum about it? More specifically, what if you use a nicer dyno-light, but one that still has a reflector that shapes the beam (a-symmetric beam) for trail riding (e.g., an Edeluxe)?

I mostly go it slow, so i wonder about real-world usability; however, dynohubs like the SON claim to be able to achieve good usable light at about 7-8mph, and even at 4mph produce the same amount of light as old halogen lamps. I'm also absolutely prepared to use a second battery powered LED headlight for the slowest uphill sections (a 2W PlanetBike LED, in my case).

Just seems nice to not have to worry about batteries failing. On the other hand, i don't want to hit any trees,... and there are a lot of those here.
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Old 10-10-11, 04:04 PM   #2
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I personally think I would have a hard time turning the crank and steering the bike correctly.

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Old 10-10-11, 04:31 PM   #3
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I personally think I would have a hard time turning the crank and steering the bike correctly.
you just need to try harder... like patting your head and rubbing your belly while on a 45 incline.
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Old 10-10-11, 04:44 PM   #4
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you just need to try harder... like patting your head and rubbing your belly while on a 45 incline.
And try not to fall off the lift while you do so.
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Old 10-10-11, 04:47 PM   #5
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Unless you ONLY ride at night,,, I'm thinking it's a pretty severe weight penalty for everyday use. I've gone to LED flaslights from deal extreme with P-7 emitters. They are light, bright, And run time is only limited by how many batteries you want to carry. Anywho you might ask your question in the Electronics and lighting forum on this site. Them geeks is way smarter than us!
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Old 10-10-11, 05:34 PM   #6
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I have no idea how much more resistance you'd have with a 26 inch wheel compared to a 700c. But, I did buy a Shimano dynamo hub on eBay and can tell you it weighs like a gold brick. I couldn't believe it when I held it in my hand. I can't wait to have the wheel built later though.
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Old 10-10-11, 06:44 PM   #7
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A dynamo won't generate enough current to drive a "good" modern LED as in the torch that B2B was referring to. Another issue is that when you get to a techy section that may require more light...you will probably slow down causing the light to dim...unless it's a smaller LED...in that case...when you reach the min current required by the emitter...the LED will just shut off. You can get past this by running a decent capacitor. If you're going to run a capacitor...you may as well just run a good LiPoly or LiMnNi pack. It would be smaller than running a dynamo+capacitor and would generate tons more current.

My double barrel XP-G lights were putting out more volume and more usable beam than the P7's in a much smaller package...and the battery pack that I made for them was probably 25% smaller and thinner than a pack of Marlboro's. A dynamo won't get you close to that in a useable package. Last time I checked, something like the Sturmey will put out 6v / 3w...but you're only getting .28 amps. An SSC P7 requires at least 1amp to be useable...2.8amps for a good strong 700-900lm with a perfect D-bin emitter. (in the real world 700-800)


There's a new emitter on the market...it's called the XM-L. If you are needing a light on a budget, the Magicshine now offers an XM-L version as well as a P7 version. Check dealextreme or Geomangear for details.

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Old 10-10-11, 10:05 PM   #8
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You needn't bother with the E&L sub-forum when we've got our own personal MTB light builder right here^
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Old 10-11-11, 07:41 AM   #9
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Originally Posted by pwdeegan View Post
I've seen references to people doing this, but what are thoughts in this forum about it? More specifically, what if you use a nicer dyno-light, but one that still has a reflector that shapes the beam (a-symmetric beam) for trail riding (e.g., an Edeluxe)?
I have an edeluxe, and it's great on the road, but the beam is way too narrow for MTB. Maybe an E3.
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Old 10-11-11, 10:45 AM   #10
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I have an edeluxe, and it's great on the road, but the beam is way too narrow for MTB. Maybe an E3.
thanks corvuscorvax. that was my guess, but i thought it might just be possible. still, it might end up being acceptable in conjunction with my second battery-powered LED, since part of the story not mentioned here is actually riding surface roads to get to the trail (and then riding those same roads back home). The actual weight of the dynohub (new SON 28) and LED is only ~180g (0.39#) more than my standard XT disc hub and a 2-AA LED light, which is negligible for me---i'll be adding far more than that in mud weight on my tires and frame.

and yes, there will be much riding in low light/night, because that's when i have free time at the moment, and winter means it's dark by the time i leave my office. such is life---whenever i can get on my bike to ride: that is the ideal time to ride.
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