Ep. 31 | Very ‘open for business’, good morning, a workhorse’s daily grind, energy +1 — hand-building a 2S2P flashlight pack for the Wurkkos SP10 and other 8.4V flashlights
Creator’s own settings as stated in the video (timestamps link to the moment). Not official values — test on scrap first.
Bill of materials
Welder, accessories, consumables and parts used in this build; quantities and specs are editable Download BOMDescription
Firefly’s ‘workhorse daily grind’: hooked on the U3 Pro, takes a cleaver to it to unwind, then gets to real work — CNC-milled copper tabs, 3D-printed four-hole holder, laser engraving, a 2S2P flashlight pack (Wurkkos SP10 and other 8.4V lights), multimeter check after welding, green heat-shrink; comments: 1mm copper plate won’t take a weld, no BMS fitted (stock has none either, a generic board won’t fit a flashlight), ‘even 1.5 nickel-plated is a struggle, badly over-rated, just returned mine’ (creator: no sponsorship money exists)
Opens with ‘I’m hooked, taking my ex’s cleaver to unwind, weld weld weld’, then ‘real work comes first’. Process (no narration, watching the footage): CNC-mill small copper tabs (comment: 1mm copper plate is a bit thick and won’t take a weld, hence small tabs); 3D-print a four-hole cell holder; caliper measurement; laser engraving; four cells (14500/16340-class small cells) go into the holder, the U3 Pro spot-welds nickel strip into 2S2P; multimeter reads about 7V (2S); green heat-shrink seals it into a flashlight pack that goes into a Wurkkos SP10-class 8.4V light; ‘open for business +1’. 73 comments: how much sponsorship did you take, even 1.5 nickel-plated is a struggle, badly over-rated, just returned mine (no sponsorship money exists); not even a BMS? (no suitable board, the stock battery has no balance board either, a generic board won’t fit in a flashlight, a small board trips output protection the moment the light turns on); thought you’d weld the copper on directly (1mm copper plate is a bit thick, won’t take a weld); CNC and Fluke too, the weak student has the most tools; will careless welding hurt the discharge cap’s life (liked by the creator).
Outcome
| Goal | Build a 2S2P 8.4V flashlight pack (Wurkkos SP10 etc.) |
| Build | 4 small cells + 3D-printed holder + CNC copper tabs |
| Result | Heat-shrunk and fitted in the light · verified on camera: Multimeter check at 255–262s; fitted at 295–310s |
Steps5 steps · click a frame to jump
1. Hooked, cleaver to unwind; then real workI’m hooked, taking my ex’s cleaver to unwind, weld weld weld; real work comes first though.
00:03 – 00:17
2. CNC-mill copper tabs; 3D-print a four-hole holder (from footage)CNC-mill small copper tabs; print a four-hole cell holder.
00:17 – 01:08
3. Caliper measurement; laser engraving; load the cells (from footage)Caliper check; laser engraving; four cells into the holder; green heat-shrink at the ready.
01:22 – 02:40
4. U3 spot-welds 2S2P; multimeter check (from footage)Spot-weld the nickel strip; multimeter reads about 7V; heat-shrink.
03:10 – 04:22
5. Into the flashlight; open for business +1The green heat-shrunk pack goes into an SP10-class light; open for business +1.
04:30 – 05:11
Bill of materials
| Small cells ×4 | 2S2P |
| AWithZ U3 Pro ×1 | Spot welding |
| CNC mill / 3D printer / laser engraver | Holder, copper tabs, engraving |
| Fluke multimeter / calipers | Measurement |
| Green heat-shrink | Sealing |
| Wurkkos SP10 flashlight ×1 | 8.4V · Target light |
Creator’s tips
- A dedicated flashlight pack follows the stock no-BMS approach; a generic board won’t fit (creator’s explanation)
- CNC-mill small copper tabs as conductors; thick copper plate won’t spot-weld
Pitfalls
- 1mm copper plate won’t take a spot weld
- Comment: careless welding may hurt the discharge cap’s life (liked by the creator)
- Comment: even 1.5 nickel-plated is a struggle, badly over-rated, returned
Li-ion safety
- 2S2P with no BMS, relies on the flashlight’s own protection (contested)
Quotes
Comment insightsanswered 4 · open 1 · corrections 2
Answered by the creator
Open questions
Corrections from viewers
No, there's no suitable board and I haven't had time to design one; the flashlight's factory battery has no balance/protection board either; a generic off-the-shelf BMS won't fit in the flashlight, and a small board trips output protection as soon as the light turns on
Reply @萤火虫:
No, there's no suitable board and I haven't had time to design one; the flashlight's factory battery has no balance/protection board either; a generic off-the-shelf BMS won't fit in the flashlight, and a small board trips output protection as soon as the light turns on
Reply @萤火虫:
No, there's no suitable board and I haven't had time to design one; the flashlight's factory battery has no balance/protection board either; a generic off-the-shelf BMS won't fit in the flashlight, and a small board trips output protection as soon as the light turns on
Reply @萤火虫: