#Supercapacitor

Step one of the jump starter is stripping it down and re-planning the layout: wide at the bottom, narrow at the top, so the cells can only stand upright; turn the capacitors so the leads go straight out, shortening them to raise output current. The original board’s wiring was a mess and mediocre quality, so it all comes out; the original main switch has very high internal resistance, so it’s removed and replaced by a switch between the cells and the capacitors — flip it and the capacitors charge, no current limiting because the capacitors are small (big capacitors and you wouldn’t need the cells at all). The original wire is solid stuff but wasn’t secured after connection, so it made poor contact. The case cabling is nice and long enough; + and − are reversed to match the capacitor polarity; wire about 5mm dia., 25mm², re-routed with length to spare; crimp the +, and add a lug to the short − lead. Remove the original BMS and measure supercapacitor internal resistance: one 2.7, the other 2.1, slightly unbalanced. Crimping lugs: not a single strand showing, crimp one side then the other, drive the force at an angle from one side to the other, use a huge amount of force so it’s tighter than stock; with no heat-shrink this big, wrap in black tape leaving only the capacitor contact area bare. Trial-fit the −: enough room, enough slack; the cells can only go in this way, switch back in place, layout solved. There are 10 cells: 12 would make 3P4S, 10 only makes 2P4S; the spot welder joins the pairs in an instant, then three upright and one across to link them in series; oven parchment (forgot the fish paper) between them because it withstands heat, so a thermal runaway won’t short straight through — heat-shrink peels off when hot and shorts both faces; jokes that his poor welding is ‘wasting the cells AWithZ sent’. Voltage fine after welding; balance leads connected (smarter to bring them straight out); tape over the welded face against punctures, then fish paper; BMS wired (an odd shape, roughly done): two thin leads charge / discharge through the BMS, two extra-thick leads short-charge the capacitors instantly. Foam padding in the case so the capacitors sit firm and a drop won’t be too dangerous; lid snaps on tight, slight wobble to fix later. Charging-circuit test: cells shorted straight onto the 0V supercapacitors, clamps glow red, current hits 40-odd A — too dangerous, could blow, must pre-charge through a ceramic resistor and only then close the shorting switch in parallel and start. Comments: someone built 3S5P 18650 + 6 × 500F in series and it struggles to start a 2.0T (creator: voltage too low, needs 4S at 16.8V to fill the capacitors); the copper lugs are sloppy; capacitor internal resistance too high; a local warns the capacitors are too small for winter (creator: couldn’t bring himself to buy big ones, not the optimal solution).