I first saw similar projects on DIY Perks, and figured it would be cool to have a giant flashlight around. After building it, I realized it is much more useful than I originally thought. I have used this at summer camps, and outdoors a lot. Using this flashlight is so much better than a smaller flashlight, because it lights up the path almost like daytime - no more need to strain your eyes to see where you will step. Unfortunately, I do not have any pictures of this being built.
The parts in this flashlight are commonly available (at least for people like me). I used a 100W cool white LED, 2 80mm computer fans as well as a spare CPU heat sink to cool it, a 150W boost converter to power it - the LED needs around 30V to operate - and an LM2596 buck converter to power the fans with around 10V so that they operate quietly. For all the high power wiring, I used some 18AWG wire from an old AC cord. I replaced the potentiometer on the boost converter, and mounted a regular, single-turn potentiometer to the case.
To power this beast of an LED, I used a small LiPo battery. I mounted it outside the case, as there was not room for inside while still allowing airflow (I also didn't want to permanently mount it anywhere). It's only 1000mah, so it does not last long under a 100W load. The main consideration for the battery is that it must be able to supply 100W continuously. I also made an 4S4P 8000mah Li-ion battery from recycled 18650 laptop cells to power this, and it lasts a lot longer, but it also about 10 times heavier - not ideal for a handheld flashlight. I also added a 1-8S low voltage alarm to keep from draining the batteries too low.
Building a custom case
For the case, I used 3mm MDF board, and cut it out by hand with a saw, all 4 sides individually. After mounting everything to the sides with M3 screws and some hot glue, I attached the 4 sides together using angle brackets and bent strips of galvanic steel strapping (to act as angle brackets). The handle was made from a piece of an old DVD drive case, cut off with a rotary tool, and bent to shape by hand with the help of a few pairs of pliers. Overall, it looks pretty good, and has a sort of steampunk aesthetic.
The next version of this flashlight will be contained within a large PVC tube, which will be much more durable than the 3mm MDF construction that I built this time. The battery will also be contained inside the unit, but ideally still be removable.
One thing to be aware of with these cheap 100W LEDs is that the LEDs are not perfectly matched. This will have the effect of some LEDs getting much more current passed through them than others, which could be dangerous and lead to fires or explosions. Use them are your own risk. There are lots of people using these LEDs and have not had a problem, but just be aware that it can happen. The best way to check your specific LED is to power it from as low of a voltage as possible - until the LEDs just start to light up. If you see that some of the LEDs are much brighter than others, it might be a good idea just to keep an eye on them, and check it periodically. Just on be on the safe side, I set the maximum voltage on the boost converter to around 31V. The max voltage for these 100W LEDs is around 33-34V, so I am not driving it as hard as I can, which does allow some headroom for unmatched LEDs.