DIY high-power flashlight tutorial: three 18650 cells and an e-bike headlight for under ¥20

A high-power flashlight for under ¥20: three 18650s (Beiliang 3.7V) spot-welded into a pack with an AWithZ handheld welder, heat-shrink and PVC pipe for the body, an LED e-bike headlight + 16mm metal push-button switch + DC jack, hot-glued together; night test reaches 150 m outdoors

A tutorial with no voice-over, just BGM and a few captions. Three Beiliang 18650s (shopping screenshot ¥9.50 each, 5550mWh flat-top) are placed side by side and spot-welded into a pack with nickel strip on an AWithZ handheld welder (0–30s), wrapped in blue heat-shrink and shrunk with a heat gun (34–49s), with red and black leads brought out at both ends. The body is grey PVC water pipe (shopping screenshot ¥2.77), marked with a whiteboard marker and cut open with a utility knife (63–98s); a 16mm 12–24V metal latching push-button switch (90s shopping screenshot) and a DC jack (148s screenshot) are fitted; the head is an LED e-bike headlight (square, multi-LED), lit up at 111s. A 50mm-ID grey PVC pipe cap serves as the tail cap (155s), the pack is pushed into the pipe and wired (171–185s), and a hot-glue gun fixes the head and the connectors (187–194s). Night test: a casual try outside the front door with the spot head while it is not fully dark yet; in full darkness outdoors 150 m should be no problem; a flood-beam version is shown for comparison (207–223s); the ending shows several finished units. Of 1013 comments only 11 were captured: the top one is ‘your 10 flashlights aren’t as bright as my one’ (the creator replied); someone warns that with no charge/discharge protection it will over-discharge and an external charge protection is needed, and asks how to charge it; the creator’s pinned comment adds ‘Demacia G40 gear 2’ as a brightness reference.

Outcome

Steps7 steps · click a frame to jump

1. 
   1. Spot-weld three 18650s into a pack (AWithZ handheld)

   Three Beiliang 18650s side by side, nickel strip spot-welded with the AWithZ handheld welder, red and black leads at both ends; shopping screenshot: Beiliang 18650 3.7V/4.2V ¥9.50, 5550mWh flat-top.

   00:00 – 00:30
2. 
   2. Wrap the pack in blue heat-shrink, shrink with a heat gun

   Cut blue heat-shrink to size and slip it on, shrink it tight with a heat gun, tidy the leads, add insulation.

   00:34 – 01:01
3. 
   3. PVC pipe body: mark and cut the holes

   Grey PVC water pipe (¥2.77); mark with a whiteboard marker, cut the switch hole and the head position with a utility knife; fit the 16mm 12–24V metal latching push-button switch.

   01:03 – 01:38
4. 
   4. Light up the LED e-bike headlight, wire it into the tube

   Test-light the square multi-LED headlight; push the pack into the PVC pipe and connect the switch and the head.

   01:51 – 02:11
5. 
   5. DC jack + 50mm-ID pipe cap as the tail cap

   DC power socket (shopping screenshot); a 50mm-ID grey pipe cap is the tail cap, drilled to take the jack; the pack goes in.

   02:21 – 03:05
6. 
   6. Hot-glue the head and the connectors

   A hot-glue gun (GLUE GUN) fixes the head base, the pipe cap and the connectors; the finished unit is a grey handheld high-power flashlight.

   03:07 – 03:25
7. 
   7. Night test: spot beam 150 m, flood version for comparison

   A casual try outside the front door; the spot head while it is not fully dark yet; in full darkness outdoors 150 m should be no problem; flood version for comparison; the ending shows several finished units.

   03:25 – 03:56

Bill of materials

Creator’s tips

• E-bike LED headlights take a wide 12–24V input, so three 18650s in series drive it directly 01:30
• PVC pipe + pipe cap makes a very cheap body; whiteboard marker lines wipe off easily 01:14

Pitfalls

• Comment: with no charge/discharge module the Li-ion cells will over-discharge and charging is awkward — use an external charge protection
• Comment: short runtime, bulky, not much use

Li-ion safety

• 3S Li-ion with no BMS charged straight through the DC jack risks over-discharge / over-charge (raised in comments)

Quotes

Cost & time