DIY light hub generator examples?

Hey guys! Been a while since I've posted here.

I have a problem that is unique to this forum, but not all that unique in general.

I wish to use a low drag generator hub like the very nice Shmidt SON hubs, but I can't.

Those hubs have an O.L.D. of 100mm, very typical of a fork dropout. The bike I'm interested in applying this to has a front hub dropout O.L.D. of 135mm - like that of a rear hub.

Wait, why? It's a Surly Pugsley:
http://dillerdesign.com/random/bike/snow/IMG_4420.JPG
http://dillerdesign.com/random/bike/Halloween_get_up.jpg (I painted it on the cheap for giggles)

You can't fit the enormous tires through a 100mm dropout while still avoiding the brake calipers. So, the dropouts are the same width as a rear tire. The wheels are technically interchangeable front and rear.

As you all know, batteries don't work so well in the cold. Almost all of my riding is done in the dark because days are short. My 2 x MagicShine headlight batteries have a pathetically short duration at 10 Fahrenheit compared to summer temperatures.

Has anyone ever made a bolt on generator for a "standard" hub? I'm thinking that I will have to fabricate my own, I just want to see if anyone else has done it yet.

When (not if) I get a second fat bike, I will make that one into an e-bike. I had originally planned to make this one motored, but my new job is so close to home that I don't even bike, so I left it unmotored for the challenge.

man forget about this hub , is power is only 3 watt and cost 250$ just for the hub not including the rims ansd the spoke , you not even close to have the power you need just to open your magicshine with 3watt of power

I second that.
Get a $10-$40 DC-DC Convertor and forget about these thingies.

If it's an ebike, and you use a generator powered by a wheel, then you are simply converting power off your pack into power for the lights, anyway, and you are actually doing multiple conversions to get it there.

It would be more efficient and less trouble to just use the aforementioned DC-DC converter, off your ebike motor pack. It'd also cost a LOT less.

If it is not an ebike you're wanting lights for, well, it's still less efficient to use the generator, vs just adding more batteries for the lights (and/or thermally insulating them somehow, to keep them warmer for longer so they keep up output longer). The generator will add significant drag to the bike if you are drawing enough wattage to run bright lights, most likely.

I don't know actual numbers, but let's say the lights take an even 10W at the input at 12V to run them. Then let's say that you can put out a sustained 100W by pedalling all the time. Let's say that 90% of that power actually gets to the road and back into the wheel to be able to run a generator. So you only have 90W actually at the input to the generator. Then let's say the generator can output that 10W, but it's only 80% efficient. So it would take 12.5W input to the generator to actually get you that 10W.

Now, assuming I haven't gotten lost in the math (possible), it's going to take 90 / 12.5 or 1/7 (14.2%) of the available power you can even output in order to just run your lights.

Most likely you wouldn't be outputting 100W continuously for very long before exhaustion sets in, so it'd likely take a LOT more than 14.2% of your average output just to run the lights.


If youre' running off a motor then the percentage of load is possibly significantly less, but it's still nowhere near as efficient as a DC-DC converter, most likely. The disadvantage of a DC-DC is that if the pack dies then the DC-DC doesn't work either, and you're stuck with no lights at all.

Good post..

But if you're at a stoplight or moving slowly, you don't have lights either with a generator light

the solution is a big ol' stinkin' pack

For being stopped at a light, a very tiny pack could work, perhaps a little bitty NiCd pack since you could let it drain really far down, and charge it back up with the generator (though of course this means even MORE power drain on your pedalling or motor, just to keep that pack recharged between stops).

Ah, but how would you regulate overvoltage / overdischarge to the battery?
You'd need some electronics to do that.

so.. unless you're amberwolf, get a dc-dc convertor :lol:

I should have clarified that this would be for a human power only bike, and I'm posting here for the expertise available on this forum.

I plan on making an electric fat tire bike, but not this one.

I've run some DC-DC converters on my road e-bike, worked really well.