Electronics, Lighting, & Gadgets - lower power dynamo hubs for LED lights?

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peliot
11-07-09, 03:36 PM
It seems to me that the standard 6W power output of the dynamo hubs I've seen is overkill for an LED light (not a super bright, just a "be seen" light). Are there any dynamo hubs out there specifically for LED lights that operate at lower power?
I imagine it would be cheaper and less resistance than the 6W ones, hence the question.

Thanks,
Pete

BarracksSi
11-07-09, 04:49 PM
There are Schmidt SON hubs that are meant for small wheels like you'd see on folding bikes. They need faster rotating speed for the same power output as their standard hub -- the same road speed with a smaller wheel means higher RPM and more power. But, with the lower power requirement of LEDs like you mention, it's supposed to be enough.
http://www.peterwhitecycles.com/Schmidt.asp
znomit
11-07-09, 05:31 PM
Its more the load than the hub. Modern hubs suck around 2W when off and are 50% efficient at driving a load (Ballpark stuff here).

You could do a simple single led light using a doubler circuit (http://www.pilom.com/BicycleElectronics/DynamoCircuits.htm#DualMode) that ran at 250mA (0.75W), giving around 100lm and under 4W total load. Would light at walking pace and provide good visibility.

tatfiend
11-07-09, 06:02 PM
It seems to me that the standard 6W power output of the dynamo hubs I've seen is overkill for an LED light (not a super bright, just a "be seen" light). Are there any dynamo hubs out there specifically for LED lights that operate at lower power?
I imagine it would be cheaper and less resistance than the 6W ones, hence the question.

Thanks,
Pete

Nominal output of most dynamo hubs, and tire driven sidewall dynamos, is actually specified as 3 watts rather than 6. At higher speed they can put out more than 3w which allows them to handle some fairly powerful lights. SRAM also shows 2.4 watt hub dynamos too.

Originally output was intended to handle a 2.4 watt headlight incandescent bulb front lights and a .6w taillight bulb which were basically little more than "to be seen" safety lights. Such halogen bulb lights are still available.

Bright dynamo driven LED headlights are a quite recent phenomenon and only started appearing 4 to 5 years ago. I suspect that dynamo hub manufacturers have not chosen to decrease power output for two reasons. The most important is that in the European market minimum dynamo output is a government regulated requirement, at least in Germany. The second is that there would not be appreciable cost savings involved in manufacturing lower power hub dynamos.

If you want battery free "to be seen" bike lights take a look at the Reelight products. They work off of magnets attached to the wheel spokes.

http://www.amazon.com/s/ref=nb_ss?url=search-alias%3Dsporting&field-keywords=reelight
znomit
11-07-09, 06:09 PM
If you want battery free "to be seen" bike lights take a look at the Reelight products. They work off of magnets attached to the wheel spokes.


+1
I run them on my commuter.
peliot
11-08-09, 06:58 PM
If you want battery free "to be seen" bike lights take a look at the Reelight products. They work off of magnets attached to the wheel spokes.

http://www.amazon.com/s/ref=nb_ss?url=search-alias%3Dsporting&field-keywords=reelight


Thanks, that's exactly the sort of thing I was looking for.