Homebrew rear Cree LED dynamo light

Leow

Newly Enlightened
Joined
Oct 12, 2004
Messages
64
Location
cheltenham uk
I've just completed fitting homemade rear lights to both my dynamo hub rigged bikes using Red



CREE LED Emitters from Dealextreme.



http://www.dealextreme.com/details.dx/sku.1776



Both of my frontlights have 3 White Cree/SSC LEDs powered by a simple smoothed rectifier circuit.

See circuit 2 http://www.pilom.com/BicycleElectron...its.htm#Basics and imagine 3



LEDS in series.



For reference my 1st light I made from the head of one of Kaidomains short run of triple Seoul



SSC P4 lights - http://www.kaidomain.com/ProductDeta...ProductId=1270

The second I bought from Saltytri -



http://www.cpfmarketplace.com/mp/sho...Light-For-Sale





I was quite happy with both lights which I also use in daylight for commuting but I was looking



around for a matching powerfull 0.5 or 1 Watt battery powered light for the rear.



If I were to put an additional Red LED in series run from the dyanmo I would suffer 2 distinct



disadvantages.

1) Low speed lighting would be worse

2) A single point failure in the wiring to the back of the bike would take out both the front and



rear lights.



BUT RED Cree lights use less voltage than WHITE LEDS.



Saltytri's light already had an extra cable coming from it that you could use to short out one of



the LEDs for better low speed performance.



So I decided to short one of the front white LEDs out with a rear red LED.





They are made quite simply. I just bolted them to some stock aluminium with a heatsink (a bit OTT?) and then almost completely potted them with a clear epoxy mixed with either orange or red glow powder from glowinc.





Front before potting



5255523856_9df0af16aa.jpg


Dynamo Backlight before potting by leofwhite, on Flickr



Rear



5255523980_6c19ddc87e.jpg


Dynamo Backlight rear by leofwhite, on Flickr



During potting



5254910487_bc6b2ec11a.jpg


Dynamo Backlight whilst potting by leofwhite, on Flickr







The 3 position switch on my handlebars now has the settings :



Left = Medium Beam (1 Led completely shorted) for riding in a group



Centre = Full beam for riding on my own at night or downhill



Right = Medium beam plus rear Red Led running at 1.25 Watt for daylight commuting and fog (it's way, way too bright for riding in a group and paints the road behind me red.





After seeing the output that I'm getting I suspect that the 0.5 watt and 1 watt rear LED lights I've seen can't be driving their LEDs very hard. If they were their batteries would have a very short life.



LeoW
 
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