Here is the finished ‘low cost’ helmet light for my bike. Estimated output on high is 270lumen.
The general overview.
The LED, driver, optics and rotary switch assembly are mounted inside a 20mm diameter square aluminium tube. The LED is a single Cree XP-G mounted on a 20mm star metal cored printed circuit board. The optics is a Ledil square RS (real sight) optics with adhesive backing. The switch is a 4 position rotary switch for off, high, medium and low in that order. The LED driver is an AX2002 bassed “kennan” driver that was modified for variable brightness. Lastly the power is 8 AA 1.2v NiMh rechargeable batteries that go in a bag on the belt when riding. The light itself is attached to the helmet with a thick strip of Velcro for quick detaching.
Some more photos.
So the the cost. With out counting the batteries or bag to go on my belt it looks something like this.
- Aluminium tube from local hardware store : $3.00
- Cree XP-G R4 LED pre mounted on 20mm Star :$7.18*
- Ldil CXP RS Optics: $5.95
- Ax2002 Based led driver board (4 to17V input):$4.30
- 8x AA Battery holder:$1.85*
- 3 pol 4 position rotary switch:$3.35*
- Battery holder Snap on connector:$0.30*
*This price is with out shipping. I live local and picked it up. All prices in the list are in Australian dollars.
Total Cost: $25.93AUD or around $24 USD.
A little over my budget of $20USD but close enough for the end result!
On high the LED draws 1A which according to Cree’s data sheet is an output of around 330lumen. Compensating for losses in the optics it might be reasonable to estimate around 270lumen out the front. More than enough for the casual night ride.
For more information on how to mod the LED driver take a look here.
Runtime is around 5 hours on high, 7 hours on medium and 16 hours on low. This is more than enough for even the longest ride. Combined with the use of low self discharge batteries the same set could be used a half dozen short rides before needing to be stuck in the charger. Very handy!
Overall i’m very happy with the results.