I was wasting time on Youtube when I came across a video where someone had made a flaslight with a 100W LED. I was curious how much they were and went to eBay to check. It turns out they’re pretty cheap at around $8 shipped. So, of course, I had to make one. I can’t claim credit for anything new as I’m using similar parts to the folks on Youtube but it was fun to make.
The 100W LED is rated for 3 Amps at 30-35V. It also puts off a bunch of heat which requires a heat sink. I could make something but there are ready made heatsinks with fans for this LED on ebay already. You also need a reflector and lens to focus the light beam. In the pic below you can see the 100W LED mounted to the heat sink with the lens sitting off to the left. For reference, I’ve also put in the smaller 10W LED I used on the Wheel Horse.
LEDs require a specific current which means I’ll need a way to supply it. I also decided I’d use a power tool battery and boost the voltage up to the 30-35 volts needed. I went back to eBay and found a DC to DC boost converter with adjustable voltage and current capability. You can see the boost converter in the picture below. The two blue potentiometers are used to adjust the voltage and current.
Before I built anything I rigged up the fancy testing apparatus shown below. I picked up a cheap 18V rechargeable lithium drill battery from Harbor Freight to use as my power source. It’s only 1.3Ah but it came with its own charger. Importantly, it was also the cheapest option I could find. To set up the converter, I first adjusted the output voltage to 30V before hooking up the LED. Then I turned the current potentiometer down and hooked the LED up with my multimeter inline to measure the current. Turning the LED away from myself, I turned it on and adjusted the current and voltage to give 100W. Then I took it outside and lit up the world.The LED was bright but I wanted to get a tighter beam out of it. So, with the current turned down, I messed with the positioning of the lens. I was never able to get to really narrow the beam though. I eventually sat down on the computer and did some lens ray tracing to see if I could figure out how to get the beam tighter. Eventually, I realized that with this size lens and emitter there’s really no way to get a tighter beam.
While I was fiddling with the lens I started using my welding helmet to avoid seeing squares because it’s bright even when dimmed. I snagged a picture of it at full power through the welding glass for you to see.
After I was done prototyping, I sketched out a few design ideas. I ended up deciding on a triangular aluminum frame. The first step was to mount the emitter/heatsink/fan. I drilled and tapped some holes in the heat sink, turned some standoffs, and mounted it to the bottom rails.
Next, I closed off the end and put the battery in place temporarily. I came up with a cross piece which links the two sides, attach the handle, and hold the panel. I also decided I wanted to be able to adjust the brightness of the flashlight while using it. To do that, I removed the current potentiometer and wired in a bigger potentiometer with a knob that I could easily adjust. The potentiometer allows me to vary the LED current from 0.4 to 3 amps. With the structure temporarily assembled, I wired it up again for some more testing. The resistor sticking up, it just there temporarily to drop the voltage for the 12V fan while I was waiting on a voltage regulator to arrive. Also, this battery pack doesn’t have a low voltage cutoff, so I’ve added a small display to keep track of the pack voltage.
Once I was happy with it, I disassembled the frame, smoothed the edges, and reassembled it with “proper” wiring. I also found I needed a glare shield to keep from shining light at myself when using it. Here’s another view. I’ve packed the voltage regulator for the fan in between the battery and end of the frame and the voltage gauge onto the battery pack. Here’s the business end.And the display.Here’s a couple pictures of the flashlight in action. The camera settings are the same in both images. On the left is the flash light at the low mode. On the right is high. High is pretty bright.
Clearly, I’m not going to get great run time with the flashlight on high. In fact, I only got about 10 minutes until the voltage meter hit 15V and I shut it down. At low though, I expect to get over an hour though I haven’t tested it. Either way its great for when you need to light up an entire yard or signal a UFO!