#Jump starter

The whole pack is welded up, with three layers of tabs on top — very solid; the charge level has barely dropped, so it should weld a lot of packs — very handy. Wiring the BMS: main + goes to +1, +2, +4 and main −; the leads are short, so extend them; red sleeve on the main +, yellow on the rest, foam pads for a first fix; trim any sharp protrusions; fix the pack first, then wire it, or it’s hard to secure afterwards. With the BMS and balance board connected it charges at 14.5V from a low-voltage supply; press the switch and it shows full, the lamp is quite bright; USB charges a phone at 29% — works, but a very slow trickle; Type-C charging shows normal, the last lamp blinking means not quite full. The main + and − ‘thick’ leads aren’t actually thick, so they’re swapped for wire a good size up from stock. With all the main leads connected and tidied, no heat-shrink to hand, so it’s bundled with electrical tape, two turns over each contact point; it fits back into the original shell exactly, with extra insulation on the main + to prevent shorts. Comments: a car draws 200–600A to start, 3P 18650 gives 60–90A at most, and with enough current the nickel-plated steel strip burns through in seconds (creator: cells picked up from a live stream, 2C is as good as it gets); does drawing power straight off the pack without going through the BMS matter (creator: discharge doesn’t go through the board); copper strip thickness and cell C-rate are both too low, too dangerous; where to buy the welder (shop window); leave a watermark to stop reposts; part 3 tests capacity.

A car jump-start pack built from a solar Bluetooth-speaker shell grabbed cheap on Douyin. The cells were also grabbed from the Douyin store, all around 2500mAh; paired with a Type-C 5V input charging board. He had built a spot welder from a microwave transformer before — hard work and poor results; then grabbed an AWithZ spot welder that runs a long time per charge, a hundred-odd yuan (an even better deal when it was ¥168), and it comes with small nickel strips. Before welding, stick insulating paper on the negative-can side so overheating can't short positive to negative. 3P4S; welder in auto mode, fires 0.5s after contact, tack one end first and press firmly; welds are clean and very solid; don't weld the middle too tight, leave a little slack — 'leave a line when welding and swelling stays friendly'; a foolproof device, very convenient. After all the positives were welded the charge was still full; the built-in battery beats his big homemade rig by far. Series: connect pairs in series, flip and connect again, main positive and main negative; measured DC voltage 16.01V, just right for a jump starter. Measured with a lead-acid battery tester as a makeshift: internal resistance 12.6mΩ, voltage 13.9V, discharge CCA 264 — should start a 2.0T car normally. Main positive and negative still need a few extra wires to boost discharge current. Test: two and three layers of nickel strip stacked both weld through solidly; conclusion, buying beats building, it's in the shop window. Comments: someone pointed out that a jump starter without copper strip makes no sense and the cells can barely do 2C (creator agrees, 'it'll do'); someone says this kind of welder uses a pouch cell that swells after heavy use and loses performance until it won't fire; a lead-acid tester can't measure Li-ion accurately (creator replies the accuracy is poor).

A car jump starter built into a solar Bluetooth speaker shell scored on Douyin. The cells were also cheap finds from the Douyin store, all around 2500; plus a Type-C 5V input charging board. He’d made a spot welder from a microwave transformer before — hard work and poor results; then he picked up an AWithZ spot welder, one charge lasts a long time, a hundred-odd yuan (bigger discount when it was 168), and it comes with small nickel strips. Before welding, stick insulating paper on the negative-can side so overheating can’t short + to −. 3P4S; the welder is on auto — it fires 0.5 s after contact; weld one end first and press down; welds are clean and very solid; the middle is not welded too tight, a little slack is left — ‘leave a line in the weld and a swollen cell will thank you’; a foolproof device, very handy. After all the positives were welded the charge was still full — the built-in power is way better than his big home-made unit. Series: join in pairs, then flip and join again, main + and main −; DC voltage reads 16.01V, just right for jump starting. A lead-acid battery tester made do: internal resistance 12.6mΩ, voltage 13.9V, discharge CCA 264 — should start a normal 2.0T car. The main + and − still need a few extra wires to raise discharge current. Tested stacking two and three layers of nickel strip — both weld through solid; conclusion: buying beats building, it’s in his shop window. Comments: someone points out that not using copper strip for a jump starter makes no sense and the cells can barely do 2C (creator agrees, ‘it’ll do’); someone says this kind of welder has a pouch cell that swells after lots of welds and loses performance over time until it can’t weld; a lead-acid tester can’t measure Li-ion accurately (creator: poor precision).