Wow, LED’s are amazing! I just fired up my Cree XM-L2 LED with a 3-cell NiMH battery pack and a 0.91 ohm resistor to keep the current under control. The circuit runs at 500 mA, which corresponds to 1.4 W for the LED and 0.4 W for the resistor… or 75% circuit efficiency and probably just shy of 200 lumens. With 2000mAh batteries I should get about 4 hours of light.
In fact I’m a little surprised I didn’t destroy that poor LED. Surface mounting the LED to the thermal substrate was definitely the hard part. I couldn’t get enough heat for the solder paste to reflow with my soldering iron so I had to bring out the butane lighter. The lighter did the job after about 10 seconds, but it left a lot of charred flux on the substrate. It may be time to invest in a heat gun!
Parts from Digikey:
- Cree XM-L2 cool white LED: XMLBWT-00-0000-000LT60E3CT-ND
- NiMH AA batteries (3): P220-ND
- Battery holder: SBH331AS-ND
- Resistor, 0.91 ohms: P0.91W-2BK-ND
Parts from Mouser Electronics:
- Bergquist Company Thermal Substrates – MCPCB: 804936
- Reflector optic: C12512_RITA-A
- Wahl Solder Paste ISO-Tip: 7459
Gregory Kimball 