Questions About DIY Dynamo Light
 

I have a Shimano DH-2N01, which is listed by Shimano as putting out 2.4 watts with 6 volts, so presumably .4 amps, but my understanding is these hubs are constant current, not constant voltage. So couldn't this hub generate more than 6 volts and 2.4 watts? Do these hubs have built-in voltage regulators?

My biggest questions are regarding the circuit components: What voltage regulator, LED driver, and rectifier should I use? I want to connect three 6 volt CREE LEDs in series. Most seem to put out about 125-175 lumens at .4 amps, so I would like to use 3 for about ~400-500 lumens combined. Does anyone have any other specific LEDs they recommend for this?

I'm new to electronics projects, but I have built simple 9V tail lights and a welder from two microwave transformers, so I'm not a complete idiot about this stuff. I just can't seem to find a comprehensive article that explains the requirements for using an AC generator to power DC-driven LEDs.

Thanks in advance!

You can consider a dyno a constant current source, but obviously things vary as the speed varies. Clearly, they don't put out as much power at low speeds.
I didn't know Cree had any 6v LEDs, which part number?

There are a lot of threads around, you may have trouble putting three LEDs in series at low speeds without a voltage doubler. Pilom is where I usually go to look for circuits

Peter White Cycles - they do specialize in Lighting systems. I did a DIY dynamo system and bought the headlight from him.

http://www.peterwhitecycles.com/

Walt

http://www.cree.com/led-components-a...-mtg-easywhite


Don't have a specific part number but it says 6V option available in description.

I think the next dyno light I build will have a single (3.7v) led. With the current output of a dyno it shouldn't need any regulation.

A dynohub feeding an LED directly would have notable flickering, especially at low speeds. This is because a dynohub puts out AC, while an LED, being a diode, will only use only half the wave. A diode bridge ahead of the LED will produce a notably better output, though it will still flicker some at lower speeds without a smoothing capacitor. You'll have to do some looking on your own about capacitor effects.

Tor

The EasyWhite XM-Ls are set up like the older MC-Es and SSC P7s in that there are four dies on one board that are either all in series or 2 parallel strings of 2 in series. They are universally less efficient than their single-die counterparts due to heat buildup on the MCPCB. If you look at the CREE product characterization tool, you'll see this. Also like the MC-Es and P7s, they are much harder to focus. Even with very large reflectors they will be floody, and they have a tendency to have dark crosses and/or donut holes in the middle due to the separation of the dies. While they are easy to wire up, unless there's a big reason to have a single unit, you're better off getting multiple LEDs and better optics.

If you have a large enough standlight you don't need a doubler. A voltage doubler does decrease your maximum brightness at the expense of giving better performance at low speeds. Ktronic did a comprehensive series of speed vs output tests for various configurations on MTBR and pretty conclusively showed that there are very few situations where doublers are useful. If you're using XM-Ls (of the single-die variety), they have such a low forward voltage at 500ma that you'll be able to get good light out of them even at moderate speeds. I run 2 XM-Ls on my dynamo system with 2 20mm Carclo Tight optics (10003). I'd upgrade the optics to something larger, like the 26.5mm's (10048), and a XP-E Red-Orange on the rear, and its pretty consistently bright.

that was a good thread, but I can't find it

http://forums.mtbr.com/lights-diy-do...-430051-2.html

Sorry, Steve Jobs deleted all my charts :crash:

^^^Thanks znomit^^^

That was awesomely informative. Thank you.