This project draws it's insperation and technical details from dan's https://www.instructables.com/id/Ultimate-Night-Vision-Headlamp---500%2B-lumens-with-/ and his https://www.instructables.com/id/Power-LED-s---simplest-light-with-constant-current/
Thanks to dan for his great instructables!
Where this instructable differs is that my four Cree xr-e LEDs are powered by a USB power supply. Any standard USB power supply will work with appropriate cables. My two main power supplies are a custom D cell holder and a Ryobi rechargeable power cell. I also have a plug in wall wart that will power the flashlight and a 12v outlet to USB adaptor that can be used to power it!
While using the D cell housing, the xr-e LEDs will put out a total of 840 lumens at 6v one amp! Standard USB delivers less power at 5v and half an amp but the LEDs still output a very respectable amount of light, maybe around 700 lumens. Unlike most flashlights this one does not produce a beam of light. It illuminates a 180 area in front of it! It's like having a 50 watt incandescent light at your side.
Building the flashlight cost approximately $40 us. Comparable flashlights on the market are probably smaller but cost in the range of $140. It would have cost me slightly more if I didn't have the electronics sitting around my basement from disassembled TVs and stereos.
This took me a while of mucking around with parts so I don't have pictures of the build. I can only explain what I did. Maybe if I build another I'll be able to take more pictures.
Update: We just got back from a camping trip and we brought the Mega Flashlight! We had a few days where we were trying to get the camp cleaned up for bed so animals wouldn't come around. Walking around with a directional flashlight makes it hard to see everything. I stood on the picnic table and was able to illuminate the entire campsite at once! Even though I wasn't helping clean directly, everything went much faster. Now even more I want to figure out how to hang the flashlight say from a tree or some other object.
Please remember to vote for this instructable for the contest!
Step 1: The USB Plug
A female USB plug sticks out the back of the flashlight. The D cell holder has a male USB so they are very happy together!
Step 2: The D Cell Housing
This was the hardest part to put together mechanically. The main tube is a chrome 1 1/4" drain pipe. A PVC end cap has a bolt through the bottom that holds a washer and a spring. The spring touches the negative terminal of the battery. The spring touches the washer and the washer touches the chrome pipe.
On the other end of the holder, I inserted a rubber stopper. The rubber stopper also has a bolt in it that contacts the positive terminal of the battery. I then soldered a wire to the bolt. I ran a wire through an edge of the rubber stopper to touch the negative pipe.
I then soldered the two terminals to the male USB.
To secure the USB end I squirted in some Gorilla Glue and let it dry then for more strength, I blobbed in some silicone caulk.
Step 3: The Power Cell
The power cell is a Ryobi lithium ion battery pack. I can put the cell in my pocket while I use the light. It's much more compact than the 4 Ds and only a little dimmer. This was 90% of the reason I went with USB, because that's the output of the power cell.
Step 4: The Flashlight
The flashlight is actually bigger than it strictly needs to be length wise but since I was using PVC as the body the dimensions were more or less fixed.
As said before, four Cree XR-e LEDs provide the illumination. They are attached to a heat sink that I pulled off a circuit board and ground down to fit inside the PVC housing. The FET came out of a stereo circuit board and the other transistor came out of a TV. I hunted down a few resisters with the appropriate values with my multi-tester and used those. I used a breadboard to build the circuit and test it using a 6v 1a wall wart that I had laying around and then later with the 4 Ds held in my hands with jumper wires on the terminals.
I did have to buy the switch. I didn't have anything but a bunch of really ugly toggles and momentary button switches.
If you want to do something similar you'll have to see dan's constant current LED driver circuit instructable.
Step 5: Future Upgrades
I would like to make a shoulder mount for the light, but haven't quite figured that out yet. It really needs to be in front of your field of vision or just looking in it's direction would hurt your eyes.
I don't know how practical or useful a head mount would be since it is an area illuminator and not just a point illuminator.
I need to find a really long male USB to male USB cord for stationary power.
A way to hang the light would be really useful, maybe something with a clamp to grip onto objects.
A magnetic attachment would also be a good idea, maybe just integrate it with the clamp?