#Lithium battery assembly

Is 15Ah enough to get work done?

A follower from out of town sent in a 48V Li-ion e-bike battery, label says 48V 15Ah Panasonic cells, made 2023-12; it feels feather-light in the hand, clearly not 15Ah, range is very short and nowhere near the kilometres the seller promised. Off with the top cover: the cells only take up a little space in the middle, the rest is foam padding, the block is very small; inside it’s 18650s, 13S3P, the wrappers carry no brand or capacity info — typical knock-off cells, you can imagine the range; this battery is worth nothing. Rebuild as 15Ah: brand-new EVE 18650s at 2.5Ah each, 6P13S; place them in the holder alternating + up / − up, lay one row first as the reference, mind the orientation and don’t get it wrong; snap the top holder on to make one block; the connecting material is 0.2-thick nickel-plated steel strip cut to the needed lengths; the welder is just an ordinary capacitor spot welder — 18650s don’t need much current; 4 welds per cell to guarantee current-carrying strength; weld the parallel and series links in order, then check the whole block for wrong or missed welds; fit the BMS, charge and discharge test, no problems and it’s done. Warning: when buying a battery, any pack whose cells are labelled CATL, Panasonic and the like is fake. Comments (343): how much for a 48V30A build (2); 12C 25P cell config is overkill, 5C is enough (2, doesn’t match this video); selling fakes is a crime, jail (1); which courier did you use (1); how much for 48V25A; how much to rebuild a Sunra; you can tell it’s only a few Ah just by looking.

A customer sent in a 48V e-bike battery case whose cells were dead. The creator measured the inside (130 × 370), worked out that 13S6P would fit, and chose EVE 2.5Ah 18650s — 78 cells for 48V 15Ah. Cells go into the holder alternating positive-up / negative-up (parallel across, series down), get spot-welded into one block with 0.2mm nickel-plated steel strip on both faces, with the main positive and negative brought out separately. The pack is wrapped in strapping tape, the BMS is fitted with its balance leads soldered to each series group in order, the input/output leads are connected, and a charge/discharge test (49.14V / 6.50A on screen) is run before delivery.

How much is the spot welder?

Can your hand touch the steel strip while welding?

Can it weld brass?

Building a 21700 five-series pack with Samsung 40T cells (INR21700-40T); the welder is an AWithZ UK1, 5V (2.4A) input, 8.4V output voltage, 1380A current, Shenzhen Juequi Technology; on power-up it has adjustable mode, gear, trigger and continuous; its pen doesn’t weld the moment it touches, you also have to press a switch — he’ll show that when welding. The kit is a Dayi A3 pin-terminal one, open it, there’s nickel inside, tip it out. How the cells go: the bent part faces this way, this is the main −, so the negative goes on this side; once in, locate the main − and main +, this is positive; join the main − first, the small nickel piece goes here; unlike the previous pen that welds as soon as it touches, this one only starts when the switch is pressed, very convenient; the large nickel goes on; flip it over, weld the main + first, then put it in; this pack is now connected. Gauge: by the way the case sits, the gauge goes at the back, red to L+, black to L−; set it in; pack welded, lid on, there’s a spring that must go in or the button won’t come back up, four screws in; find an A3 tool and try it; have you learned to weld a pack now? 159 comments: where to buy brand-new genuine cells, JD / Taobao / Pinduoduo are full of fakes (3); are 5 × 4.0 reliable, EVE 40P for about ¥100 (2); how much is the welder; tabless vs Sony C6; which welder for copper shims.

Is it suitable for a demanding Li-ion repair technician?

Bought a complete Boston Swing 5300 Li-ion pack at a scrapyard for ¥30 (a single cell normally goes for ¥8–9); 5 of the series groups are fine, each parallel group about 3mΩ, one group has two dead cells; bought two replacements on Douyin and there is a complete 24V pack; it is no good without a BMS, and he happened to pick up another pack with a BMS to fit to this one. Repair: weld the nickel strip on with the welder (a bit crooked; the welder is very easy — press it down and one click, bang); push the cells into the holder in order, insert from the front, flip it over and weld the underside too, leave some room to move; very solid; the portable welder is just like a power bank; not a neat job but it works; the welding pen tips need regular cleaning, they oxidise and cause poor welds (the pen got hot); ugly after welding but very solid. This parallel group measures 3.5, the others are all 2.9–3.5; three are welded, keep welding the rest into one strip, rough but solid. Total voltage 24V, internal resistance 19.8mΩ, nearly 20. Fit the BMS: the salvaged one, opened up, was cracked and water-damaged, no good, buy another. Discharge test: multi-function tester clipped on at 25V, two H4 bulbs (yellow + green together is 24V, black-yellow / black-green is 12V, don’t mix them up or they burn out), sparks flying, discharge current 10.8A (about 261W), no problem; the voltage drops fast because one group isn’t full — charge it up and test total capacity when the BMS arrives. Comments: with hands like that, thumbs-down for not building your own welder; AC or DC resistance meter (seems to be AC); it’s got some years on it (five or six); what resistance and what C rate (single cell 22mΩ, new 13mΩ, 3–6C discharge, mine I reckon 1C is fine); what is it for (storage / backup power); this kind of welder won’t hold on these cells, goes intermittent after a while; chicken-poop welds.

Does this board use the same port for input and output

Can this be used as a motorcycle jump starter?

Is this DC or does it charge?