#Go viral

Someone teach me how to hand-build a welder!

Straight short, ‘blew it up, bro’, cotton swab from the bag to wipe his hand — just got cut by the nickel strip again, the welding pen touched the strip and blew twice; the corner of the strip went in and it ‘burst like tomato juice’, this build really wrecks your hands. The 50A copper lug connected and a dab of solder on it; meant to spot-weld it onto the copper plate but found the lug too thick, so back to the old way, screw it, heat-shrink over it, onto the copper plate, then spot-weld to the main positive and negative; when soldering the leads the positive must go to the red positive, get it wrong and it blows up again. Nearly blew it up again just now: welding the main negative, this pen isn’t fully wrapped, it has a gap, the gap touched a positive, bang, the cable was ripped straight off, terrifying, the cable feels unsafely designed — not fully enclosed, and yes enclosing it hurts cooling, but I keep touching other things, clip another strip and it blows; same recipe as before: high-temperature glue, then cutting paper, then a layer of fireproof board on top, this corner is the blackened spot; the short blew right at the pen; this time the main +/− get sealed with 704 silicone first, then a few turns of fiber tape and the sense harness can be soldered. Comments (116): sleeve the pen in nylon braided mesh (noted); my pen is identical and it blew straight through the 50 mm² welding cable, only a few strands left (that bad?); wrap it in polyimide film; no BMS? not on LiFePO4?; solder the main +/− straight onto the copper plate (I prefer screws); safety first (scared stiff); running deliveries in Changsha.

A detail lesson for beginners. After the fish paper is on, always write the series-group number at each position, so the connection order lines up. Mark and cut the 0.2 copper strip (it’s quite heavy), punch holes in it: when soldering, twist the wire into the hole first, then add just a touch of solder, then seal with a dab of glue. Connection logic: on the first face join 1 to 2, 3 to 4, 5 to 6… up to 10; on the underside the matching positions are 4–5, 5–6, 6–7, 7–8, 8–9, 9–10; group 10 gets a long strip across to the far side; flip over and do 11–20 the same way. Someone said laying that piece on top is dangerous — it isn’t dangerous right now because the underside isn’t connected yet; once the underside is connected, laying it like that will spark. Join it cluster by cluster: finish this side, flip, then join the matching face — never connect the wrong ones, a wrong connection is a short that blows you up, bro. Settings: AWithZ P60F, gear 587, settled after a lot of trial runs; it tests your technique: copper strip underneath, nickel strip stacked on top, then weld; trim the surplus corners. When you flip, the two cells joined underneath on this side must not be joined again on top, or it shorts; group 20 is effectively the main positive; laying four like this is fine, laying six like that shorts; you must have respect for it — getting blown up is truly terrifying, no joke. Partway through, lift the strip now and then to check the welds are solid — the gear has been tuned countless times but still check. Continuous welding makes the pen hot; 4 pieces on that side, 8 on this side, then 3 more — 11 pieces — off to the evening rush to deliver orders, more when there’s time. Comments: is it Jiashikai 32140 (Jiashikai); copper strip 0.2×40? (0.2×50); can the UF20B stack 0.2 copper (no; with a nickel base it can stack 0.1–0.15 copper); building a 6045? (yes); which gear? (P60F has 999 gears, I use around 600); everyone says AWithZ is junk, is it true; when will you upgrade to laser welding.

Opens with a burnt hand by accident; looking at the delivery-order numbers these days, no more grind — home for National Day, with gear: multimeter, AWithZ spot welder, the ‘fake’ cells bought online (a joke), a small soldering iron, solder wire, the bought cells, nickel strip; also found a power bank at home (3.7V 10,000mAh) and opened it — of the five cells, three are different and not connected together, two are connected; turns out those three are fake Li-ion cells, ‘fake Li-ion cells have such a long history’; measured no voltage on the three, removed them with the iron; red +, black −; the good ones and the new cells go in parallel and back in; nickel-strip leftovers, only this tape at home for insulation. At the key moment out comes the AWithZ spot welder, because it’s small and light — bringing the big welder home would be too heavy and a hassle; screen shows gear 3.2, ‘set it to about 5’; 0.15 nickel-plated steel strip is a lot thicker, a layer of 0.1 stacked on top; welded, + and − soldered with the iron; (BGM) hand straight-up burnt with a blister; power bank assembled, charge the phone as a test before fitting the shell; shell glued on. Comments: the pulse is too long, it’s arcing (so that’s it, thanks); get an internal-resistance tester and match cells, it’ll last longer (coming later); a nickel-strip short did it (stay safe); can it still be saved (isn’t that what you’re doing); put those two in as well (they’ve been around too long, no good).

Jidian Yanjiusuo (Electromechanical Lab) builds a 16.8V screwdriver drill pack. The BMS negative is at the top-left, so the cells are laid out in the BMS’s order; spot-welded with an AWithZ H2 (screen reads 25°C), the excess nickel strip trimmed off, negative and positive welded; the cells are tinned; a small piece of nickel strip is welded on to make soldering the leads easier; fish paper stuck on; the BMS + and − soldered; the two leads at the bottom of the pack soldered; foam stuck on; into the case for a test, a ‘high-power power Li-ion battery, charge once every two months’ sticker applied, test fine, done. Comments ask which welder / how much the welding pen costs, whether the nickel strip is 0.1 and too thin, whether four cells in series is enough capacity; one suggests just welding on a small piece of nickel without tinning.

The soldering iron hasn’t been lasting lately, so a new battery from 8 × 21700 — Lishen cells pulled from floor washers and the like, IR around 9–10. Using the AWithZ H2 handheld spot welder; the strip cut in advance wasn’t enough, so more is cut; no holder, because the waterproof box is a fixed size and with a holder a battery this big wouldn’t fit, so the cells are hot-glued instead. Welding done, pack voltage measures 14.43V; old battery removed; the new BMS hasn’t arrived so it isn’t fitted yet, just solder on the two + / − leads. Comments ask whether the IR meter is any good and for a store link, and why not use fibre tape for a sturdier build.

A friend picked up a lot of power-tool batteries at the scrapyard and wants them made into 12V. Remove the BMS from each battery: undo two screws, a little solder on the iron tip, lift with both hands and it comes off; do the same on all of them (cells marked 18650 1500mAh/5C); peel the nickel strip off one by one — careful not to short, this step shorts and sparks extremely easily, one slip and it looks like this (sparks on screen); wipe every cell clean, grind the weld spots off with an angle grinder so they weld well; IR-test each cell’s voltage and IR with the IR meter; pre-cut the strip plus the two main + / − strips. The AWithZ H2 handheld welding pen arrived today, give it a try — long-press the bottom to power on; tack the two ends of the pack first, then weld the whole thing, the welds look very good, 0.12 strip is easy. B+ on the BMS to the positive, held with insulating tape, four wires soldered on; BMS output measures 11.77V, OK; solder the output leads; everyone, do the insulation properly or it will spark; the blue heat-shrink ran out so no shrink wrap. Comments: ‘professional or not, shorted twice’; what use are old batteries; mine is 48V.