Most of us have seen this by now, and those of us who Make or just curiosity, know they have batteries or capacitors to power the flashlight.
Well, I have good news for hand crank flashlight owners all over the world. The generator makes almost identical power as a computers’ USB port and not only can you install a USB port on your flashlight to charge any peripheral via USB, I’m gonna show you how.
Since I have modified two flashlights, they have already presented different situations for building the port inside the flashlight.
Warning. When entering the flashlight, there is a system like gears in a clock. With both of my flashlights I have been able to work it apart carefully, to explore the inner case without it falling apart.
To begin, there are a few screws to remove so you can explore the negative-space-recesses for implantation of the USB port. This is the first step, to make sure your model of flashlight can be modified. Second, is to have the very few parts needed to finish.
4 diodes 1N400X series to build the rectifier, the USB to adapt into the flashlight and small wire, 20 or 22 gauge to wire it. Preferably stranded wire for the flexibility.
Once upon a time I didn’t know what all of this terminology meant, but through patient reading and trial and error I was able to do this, and even if you don’t understand how this mod works, you can still make this then understand it later.
Unless you have an acute awareness of what you are doing when you wire this together, you have to use a voltmeter to determine polarity.
As you look at the USB port, and hold it at the proper angle to reveal the metal contacts. The one on the left is negative and the one on the right is positive. There is no purpose for the two contacts in the middle for this mod. So, keep in mind if the contacts are upside down, the contact on the upper left is positive. When you wire the positive contact in the back, make sure it doesn’t come in contact with any other metal, except the wire you are soldering to it.
Since you need a rectifier to convert the AC to DC, I made one. Rectifiers can look different, but they will always route electricity one direction. So, since I wanted to make the oscilations of AC to DC, I needed a rectifier.Earlier, when I mentioned the voltage was almost identical, once rectified using the diodes, when cranked it puts out half of the amps and within .5 volts as normal USB does.
If you are having trouble soldering the wires or contacts together, try tinning.
Use the iron with solder on the tip. As the twisted leads heat, the solder will move throughout the groves. This is known as tinning.
If both points are properly tinned when you add the iron temporarily, the solder melts, then remove the iron. The solder then solidifies and you’re set, a good connection. When possible, anchor wires mechanically, like the holes in each generator lead, the wires went through the hole then I bent the wire up.
In the pictures I kept the orientation of the rectifier showing the ground on the left, the positive on the right, and the AC connection on the remaining points. I also tinned the twisted intersections to make it easier to solder the wires to them, and make a stronger connection. If you don’t know why this converts AC to DC, pay attention to the stripe on each diode. This identifies the ground side of the diode. In any picture of the wired rectifier, notice the stripe orientation to the ground and positive wire. On the left side, the stripe is close to the AC connections. This means that electricity of any form cannot travel that direction. On the positive side, the stripe is furthest from the AC connection. This arrangement of diodes allows each cycle of AC, to be “Directed” in one direction.
I used Gorilla Glue to help stabilize the USB port, when I would push the USB plug in, it would move the contact out.
Step 1. Pay attention to where you will cut out the window on the flashlight for the USB port. It has to be reassembled when you place the USB, and you will be running wires, just give yourself room for your mod. To make this slot, I used a combination of proper size drills and files. A caliper comes in handy for measuring the exact rectangle to place the USB. I just scratched the points of the calipers into the flashlight for guides.My first mod, pictured above, was a well-hidden port. The USB was covered when the handle was retracted.
Locate the generator. In this case the two white wires go to the flashlight’s rectifier to charge the batteries wrapped in the green shrink wrap.For this mod it is important to wire directly to the generator so it does not tax the batteries when a USB cable is plugged in. It will only work when you crank. You will also charge the batteries for the flashlights whenever you are generating. Since it generates AC it won’t matter which of the two wires go from the generator to the rectifier. I’ve noticed the batteries are only 40ma, you don’t want to use this battery to charge another battery, it just doesn’t have the capacity. For example, a single AA has up to 2500ma.
Step 3. Solder together all components in order, generator, rectifier, to USB. Keep in mind polarity from rectifier to USB. Now it matters which wires go where.
Step 4. Electric tape all solder connections and the rectifier then reassemble the lid. I made this piece with a notch in it so it could passed at the base of the wire then folded on itself.
Once it’s all wired up, you can use a USB cable that has been cut off to test the voltage, amp and polarity. 
Step 5. Secure USB port to flashlight housing.
I use gas tank repair, it’s cheap. Cut off equal size compound, mix putty together thoroughly.
Press around the USB on the inside to support it. Let it dry over night.
BMG Micro has USB ports for .45 if you can’t find something to harvest from.
You should be able to find blocking diodes 1N400X series for .02 per unit in a roll of 100. They are handy to have around anyway.
