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Old 09-16-09, 07:42 AM   #1
Zaphod Beeblebrox 
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Dynamo powered Cree LED's electrical Q's

I'm looking at parts to build myself an LED headlight to be powered by a Sturmey Archer Dynamo hub. The hub is rated at 3watts at 6V. I was thinking that I'd use a single Cree MC-E as the main headlight. It provides 430 Lumens at 350mAh.

I have some knowledge of electrical circuits, but this is my first try with LED's
Please correct me if I'm wrong.

My idea is to simply wire the LED to a 350mAh buckPuck or similar and plug that into my Dynamo hub.

My question is regarding adding more light. When I want to add more LED's (for taillights lets say), Am I better off to wire the taillight up to its own driver and run two connections out of the Dynamo, or is it best to get a driver that has some room to grow and add on to that?

I'm also getting confused trying to calculate the total forward voltage of the system if I were to use 2 or 3 LED's on one Driver. All I can figure is that I'd need a boost driver rather than a buck, but I'm not sure whether the 3watts my hub can put out will be sufficient for that.

any help is much appreciated.
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Old 09-16-09, 09:10 AM   #2
unterhausen
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You need to reconsider your choice of leds with that dyno. If you use it in parallel, your hub doesn't have the amperage, in serial, you don't get good low speed performance. The buckpack doesn't do what you need either.

I'm using a triple cree xp-e with my Shimano. I threw together a voltage doubler circuit just to get it working, now I need to do a better job.

I have one of the Sturmey Dynos. I'm thinking about just using an XR-E on the front and rear.

There are some good threads on Candlepower and the MTBR light forums.
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Old 09-16-09, 11:20 AM   #3
cerewa
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Am I better off to wire the taillight up to its own driver and run two connections out of the Dynamo, or is it best to get a driver that has some room to grow and add on to that?
looks like the LED you're looking at is intended for about 3v 350mA, or about 1 watt. If you want, it looks like you could just run two identical LEDs in series with no voltage regulator, connected to the 6 volt dynamo (so that each LED in the series pair will receive 3 volts.)

Last edited by cerewa; 09-16-09 at 11:28 AM.
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Old 09-16-09, 06:03 PM   #4
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Martin has dynamo LED circuits and information.
http://pilom.com/BicycleElectronics/...lectronics.htm
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Old 09-16-09, 10:32 PM   #5
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dynos act like current sources, so you can probably get more than 3w out of it.
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Old 09-17-09, 03:11 PM   #6
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The Cree MC-E puts out 500 to 700 lumens at 2.5 amps. 350 mAh would drive it on low.
An XR-E R2 might be better for your use.
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