I found an old Black and Decker Snake Light at a thrift store last year, I thought they were kind of cool when they came out in the 90's. I quickly modernized it with a 1w LED in it immediately which improved the battery life, but it still used plain old C batteries, still I passed on the later Versa Pack version at the store.
Not too long ago I was in a discount-discount store and I saw a Power Bank that extends the life of a phone and I had an epiphany. For $5 bucks I picked up the rechargeable battery that charges batteries.
Step 1: Tools and Materials
- Soldering iron and solder
- Hot glue gun
- Small flat head screw driver
- Safety goggles
- Flashlight (preferably one that comes apart at both ends... or a Snake Light)
- Power Bank
- Length of small gauge wire
- (not shown: LED and resistor)
Step 2: Disassemble Power Bank
With the small screwdriver I carefully pried the case open, it just snaps off, no glue. I found a 18650 3.7v Li-ion 1800mah cell with a PCB on it.
(You really need 5v to charge a phone, this just prolongs the life of the phone in an emergency, when you can't find a wall outlet.)
Step 3: The Build
Before I mentioned that I put a LED in place of the old krypton bulb or whatever was in it. It's a cheap 1w LED on a 20mm star board with a 3.2 forward voltage. I didn't even use a resistor with it because the C batteries made 3v.
Since this battery is 3.7v I would need a 1.5 ohm 1w resistor for this 1w LED bulb (1w resistor would dissipate heat better than a 1/2 or 1/4w). A 24 ohm resistor is the smallest I had at the time I did this. I want to try a 5w bulb so I would try a 1 ohm 1w resistor.
Here's the calculator I used... ledcalc.com
They also have direct fit LED flashlight bulbs like the Rayovac brand you can pick up a Walmart. I just don't know what the specs are on them though.
- Take apart the light of your choice and find the battery terminals or wherever you'll need to send power to the bulb, if using an LED find which terminals are positive and negative.
- Solder wires from the battery leads on the Power Bank to the flashlight. (You can see the resistor on one of the ends.) Take care not to heat up the battery or circuit with the iron.
- Situate the battery inside the battery compartment. I put the USB portion to where I could easily access the ports and still put the battery cover back on.
- I used hot glue to mount the battery assembly, I put a little glue around the battery too. I glued everything down good, but I didn't completely smother everything to where it couldn't "breathe".
- Reassemble flash light.
Step 4: The Test
Well it works as a rechargeable flash light now while keeping the vintage looks, which is what I wanted. It's also nice that I can use a ubiquitous micro USB to charge it. And as a side affect doubles as a phone charger / prolonger.
I wouldn't use the light while charging the battery, I'm not sure if the Power Bank would like it in the long run. Don't leave the light with its Lithium-ion battery in the blazing sun either.