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  1. #1
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    adapting from our environment, some newbie questions :-)

    so a little background, my city bike was stolen a few months ago in Lisbon and the replacement I got is a Winora German trekking bike, already set up with a bottle generator, front light (B&M) and a taillight. It has the SMS fenders that are part of the circuit and it all works pretty well.

    cut to me not being able to leave well enough alone. my point here is more to play around with what I have than to create the ultimate new night rider, just in case this seems a bit pointless.


    I found a cheap replacement house light using 30 LEDs to replace a 35W MR16 bulb, similar to this:



    the specs on the package are 2W, 30 LED, 12V 50Hz. upon opening it and reading the resistor codes (by way of an online resource), there are ten 180 OHM resistors in parallel, with three LED's in series per resister, I have found that there is a 12V bridge rectifier to make it DC (I'm in Europe so 230V). I have no idea what specs the LED's are, but I don't expect they are super high end.

    I have desoldered the bridge rectifier and I want to use this with the 6V, 3W bicycle generator (this 2W bulb and another 1W, 21 LED for the rear) Upon connecting the light to the generator it will light and seems to have good power, but I want to ask if I am running the risk of burning out the generator over time trying to power it with too much current (if P=VI halving V means doubling I)? or running too much current thru the LED array? or am I just underpowering the lamp with too strong of resistors?

    I know that the generator is variable output, and can reach high voltages (maybe 8V?) at high speeds going downhill. I am assuming that the 12V rating of this circuit will protect it from overvoltage, but am I really wasting a lot of energy running this at half voltage with resistors meant for 12V?

    Thanks for any advice on this, I know just enough to get myself in trouble and college physics class was a long time ago. I just want to try it and see how comparable it may be to the current incandescent bulbs, but without hurting my existing components in the process

  2. #2
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    Usually these kinds of lights run happily from 6-18v without any difference in output so i think it will be no problem at all running this setup. The only problem i see is that the light will not start to work until you reach its minimal power requirement.

  3. #3
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    Those lights are normally nowhere near as bright as the 35W halogen. I'd look into something else.

  4. #4
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    Thanks Bryank, but I'm not looking for the 35W halogen, but I agree for house lighting 2W LED's are not really cutting it. ;-)

    good info so far that I'm not going to blow the lights, how about the generator? :-)

    thanks all!

  5. #5
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    well I thought I would make an update to this thread, (if anyone gets it to load is a separate issue)

    I got my dynamo hub built, as well as the household LED lights all rigged up. I used a 2W front (30 LED) and a 1W rear (15 LED). I ran them for a few weeks on the bottle dynamo setup and they worked just fine. Not super bright but decent for city biking where they are more important for being seen than seeing.

    then I installed the hub generator to the system, and it was great. Very low rolling resistance, quiet, all those great things people say about them. I was very impressed at the extent of the low rolling resistance, it was really unnoticeable.

    Then I caught my homemade LED headlight on the front door and ripped it off the mount :-( While I worked on remodeling it, I hooked up the standard Halogen B&M light that was on the bike.

    All of a sudden the rolling resistance went dramatically up!! I could really feel the drag, and it was obvious in just spinning the wheel by hand.

    so I got the LED lights and the B&M both working and during the replacement, timed both systems. a very basic test, but with marked results.

    spinning the front wheel up to a higher speed (+/- 15km/h) by hand and timing how long it took to come to a stop from 12 km/h; I got about 20 seconds with no lights on (an average of multiple tries).

    with the same test and the halogen light the wheel bumped to a stop in only 4 seconds!!

    then with the LED lights connected it rolled to a stop in about 17 seconds.

    so, while I didn't think I was really getting any benefit from this exercise other than my soldering practice (i.e. not a brighter light), I found that the efficiency of the LED really makes a difference in the drag overall.

  6. #6
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    Yep, led's are much more efficient. An incandescent lamp outputs about 10% of the input energy as light, the rest of the energy is output as heat. Led's output about 80% of the input as light. The incandescent lamps are good for warming the environment, not as bike lights! What kind of hub genny did you get? There are several circuits around to maximize the output of the the hub gennys for led's.

  7. #7
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    I got a Shimano DH-3N80 hub online and built my first wheel around it, worked out great!

    I'd be interested to hear more about the circuits you speak of, even just something with a capacitor to help even out the flicker :-) it seems to do well, lighting brightly at even just 6km/h, but a steady light needs a decently higher speed

  8. #8
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    I got a Shimano DH-3N80 hub online and built my first wheel around it, worked out great!

    I'd be interested to hear more about the circuits you speak of, even just something with a capacitor to help even out the flicker :-) it seems to do well, lighting brightly at even just 6km/h, but a steady light needs a decently higher speed. I've experimented with just adding a 16V 1000uF capacitor in line, but it really didn't do much...

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