A quick post today to show off my latest 3D printed design, a battery box to replace three D cell batteries with one 18650 lithium-ion rechargeable cell that is charged by a cheap onboard charger and step up circuit board.
My need to create such an adaptor is because I found an old 1970s torch in my stuff that I had received as a kid. I wanted to keep it in usable condition, but I didn’t want to keep D cell batteries on hand. Knowing that this torch took 3 x D cells which are 1.5v each, I decided to use 1 x 18650 rechargeable battery that I have plenty of in stock. Often used in laptop batteries, 18650 cells are generally rated at 3.7v, but I have seen plenty that measure over 4v. The answer to keeping the output of my adaptor at the correct regulated voltage was to use a step up voltage converter PCB that also handles the charging of the 18650 cell. These type of boards are very cheap from China and I went with this one below from BangGood.
Additional components I used were an 18650 battery holder, some screws, 2 spade connectors, a washer and I also 3d printed a case so there are no modifications to the original torch itself. The washer was used on the end cap in order to make contact with the screw that is connected to the negative output of the charge board via the spade terminal.
Wiring it up is as simple as the below diagram with only the battery holder and output wires needing soldering to the main PCB. If you were remote mounting this PCB in a bit of old gear and can’t access the USB charge port there is an option to solder input wires on either side of the charge port.
The final step before powering up your device is to set the required output voltage via the onboard variable resistor. A digital multimeter is a necessary to get the correct voltage that is required by whatever you are planning to power up.
If you want the STL files for my 3d printed case you can download them from thingiverse here.
Wrap Up
This was a fun quick project that recycled a few old parts with a few new parts and avoided an old torch going into landfill. It’s not pretty, but it is functional and hidden from view once in the torch. If you have created a similar project with a similar charge board let us known in the comments below.
Resources
3D print design files link
Step Up PCB
18650 battery holder
Screw Kit