Introduction: Rechargeable 3 Watts Flashlight

The flashlight built in this Instructable is fully 3d printed and runs on a 18650 rechargeable battery. It is a little challenging to build if you are interested in enhancing your maker skills. It requires a small amount of supplies, and I decided to share a version without a LED driver since 3 x 1watt LEDs are inexpensive and flashlights might not be used as often as household lights, therefore a reduced lifetime might not be as dramatic.



3D printer

solder iron

hot glue gun



4 different 3D printed parts of the flashlight

3 x 5mm 1 Watt LED (3 Watt LEDS are available in the same package, this would give you 9 W total, but you would need to recalculate resistor values)

1 x diode with a 0.6 forward voltage drop (important, as it will be explained further below)

1 x roll of electric wire (around 1m)

1 x box of heat shrinks

3 x 39 ohm resistors (ideally, test your LEDS and apply V=IR to determine the best value to reach 320mA)

1 x pre-built USB single cell recharge protection PCB

1 x 18650 rechargeable cell

1 x pair of Silver Tone Metal Battery Spring Plate connectors

3 x M1.4 screws

Step 1: 3D Print the Required Files

Links to the files will bring you to Thingyverse, where you can download the 4 required files to print the flashlight.

Step 2: Soldering Parts of the Schematic

Start by soldering 20-25 cm wires to the OUT-, OUT+, BATT-, BATT+ terminals of the battery protection printed circuit board. The OUT+ wire should be shorter, around 5-10 cm since it will connect to the power switch located right next to the protection circuit board.

Solder the 3 resistors to a piece of perfboard to maintain their position when the flashlight is completed (note that a single resistor could have been used on the other side of the LEDs).

Solder a small piece of wire to the 3 leds to help them reach the resistors later on.

Step 3: Assemble First Terminal: BATT+

*Do not forget adding a 2 cm shrink tube before soldering the wire!

Solder the diode you chose with a voltage drop of around 0.6 V to the tip of the BATT+ wire. Solder the positive battery connector to the other side of the diode, while making sure its cathode (negative side, normally has a mark) is pointing towards the PCB and the rest of the circuit. The diode is important since most circuit protection circuits like the one used in this Instructable use DW01 as a protection chip, which cuts voltage at 2.4V, which is way below a safe voltage for a 18650 cell. With the 0.6V drop, the cutoff voltage becomes around 3.0V, which is much safer and better on the long run for your battery.

Step 4: Assemble Second Terminal: BATT-

This is the trickiest part of the project. Again, do not forget the shrink tube before soldering.

This part only requires to solder the negative battery connector to the BATT- wire.

Once this is done insert the wire in the flashlight's enclosure while making sure you place it next to the connector socket on the 3D printed body, orientated towards the side with a wire mark, like shown on the picture. This should be easier with a pair of tweezers

Use a glue gun to drip glue down on the battery connector to secure it in place.

Step 5: Assemble Third Terminal: OUT+

Insert the power switch in the bottom cap.

Solder the short OUT+ wire to the power switch. Solder a 20-25 cm wire from the second terminal of the switch, and leave it like that for now.

Step 6: Glue the PCB to the Bottom Cap

First, make sure the PCB fits correctly into the slot so that the USB port is easy to reach from the outside like shown on the image. You can cut a small corner of your PCB if needed (make sure you do not cut any copper trace off as your PCB wont work). Apply hot glue on the plastic panel and place the PCB on it. You can add hot glue around the PCB to secure it in place.

Step 7: Add the Wrist-loop

Slide a rope or wire of your choice through both holes of the bottom cap. Tie a knot inside the cap and pull on the rope to free the wrist-loop.

Step 8: Pass the Wires Across the Enclosure

Move the wires connected to BATT+, OUT+ and OUT- across the flashlight's body. Then, pass the OUT+ wire across the light cap (red on the picture).

Step 9: Glue the Positive Connector to the Cap

Step 10:

Use electric tape or blue tack to secure the 3 LEDs in their sockets on the small 3D printed cover while soldering the 3 negative terminals of the LEDs together. Solder the OUT- wire to the LED negative terminals too.

Solder the resistors to the OUT+ wire, while making sure the OUT+ wire is still through the top screw cap. then, cut off the excess resistor leads to prevent shorts, and leave just enough to solder each LED wire to a different resistor.

Step 11: Insert the Battery, Screw the Cover and LEDs to the Screw Cap

Put the 18650 battery inside the enclosure and screw the cap in place. The circuit is completed so test if the flashlight is working before proceeding to the last steps. If it doesn't light up when turned on, time for debugging! Are all the terminals soldered? Are the LEDs connected properly? Review the whole circuit with the help of the schematic.

Shove the wires inside the cap and screw the cover with the M1.4 screws.

Step 12: Done!

Please give feedback if you try this as it is my first instructable. I also noticed there were other flashlights available on this site, this is not a spin-off! I created it myself. Thanks for reading and happy camping!

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