Building a 24V Li-ion battery from 16 × 32140 cells

Master Zhang (Li-ion) builds a 24V30Ah pack for a follower’s electric wheelchair: Jiashikai IFR32140 15Ah LiFePO4 ×16 (8S2P), alternating + / − rows in holders, fish paper on the positive ends, 0.2 nickel-plated steel strip, capacitor spot welder at gear 30, 3 welds per cell = 6 spots, welds checked; 8S LiFePO4 BMS (Bozhi BZ808 30A) with the harness soldered to the tabs in order; shaped flat to fit the battery bay; charge / discharge test; comments: many asking for the welder link / price

Building a 24V Li-ion pack for a follower’s electric wheelchair; single 15Ah LiFePO4 cells, Jiashikai 32140 (label IFR32140-15Ah 3.2V 48Wh; capacity 15.60–15.75Ah, internal resistance <2.5mΩ, voltage 3.293–3.298V). LiFePO4 is 3.65V per cell, so 24V needs 8 in series; 30Ah needs 2 in parallel, 8S2P, 16 cells in total. Laid into the holder alternating + / −; fish paper on the positive ends for insulation; laid out and locked in with the top holder; with the holders on it is very rigid, there is a gap between each cell, good for insulation and safety. Welded with 0.2 thick nickel-plated steel strip; a capacitor spot welder with the current set to 30 welds 0.2 nickel-plated steel strip easily; each cell is welded 3 times, 6 weld spots, so current capacity is assured; after welding every spot is checked for loose welds. Fitting the BMS: a LiFePO4-specific 8S board (Shenzhen Bozhi BZ808-5080-030C30-B-F-8S, 8S 30A LiFePO4, common port, balancing, temperature control); the harness is tidied and soldered in order to the matching tabs; with the BMS on, the 16-cell pack is shaped very flat to suit the battery bay; finally a charge / discharge test. 191 comments: how much for Jiashikai 32140 in 72V45Ah (4); how to build 96V30A for a two-wheeler split into two locations (2); where to buy the welder, want one (1); how much for 12V20Ah (1); how much for 48-30 (1); 3.65 × 8 = 24V (1); OK for a trike (1); is the AWithZ welder any good; welder link please; don’t use this pack on a big delivery e-bike.

Outcome

Steps6 steps · click a frame to jump

1. 
   1. The job: wheelchair 24V; Jiashikai IFR32140 15Ah LiFePO4

   Building a 24V Li-ion pack for a follower’s electric wheelchair; single 15Ah LiFePO4 cells, model Jiashikai 32140; label IFR32140-15Ah 3.2V 48Wh.

   00:01 – 00:15
2. 
   2. LiFePO4 3.65V per cell → 8 in series; 30Ah → 2 in parallel; 16 cells

   LiFePO4 is 3.65V per cell; 24V needs 8 in series; 30Ah needs 2 in parallel, 8 in series; 16 cells in total.

   00:15 – 00:28
3. 
   3. Alternating + / − in the holder; fish paper on the positives; top holder locked on, rigid with gaps

   Lay into the holder alternating + / −; fish paper on the positive ends for insulation; once laid out, lock the top holder on; with the holders on it is very rigid; there is a gap between each cell, good for insulation and safety.

   00:28 – 00:55
4. 
   4. 0.2 nickel-plated steel strip; capacitor spot welder (UF20B) gear 30; 3 welds per cell, 6 spots; check the welds

   Weld with 0.2 thick nickel-plated steel strip; the capacitor spot welder with current set to 30 welds 0.2 easily; each cell welded 3 times, 6 weld spots, so current capacity is assured; after welding check every spot for loose welds.

   00:55 – 01:22
5. 
   5. LiFePO4-specific 8S BMS (Bozhi BZ808 30A); harness soldered to the tabs in order

   Fit the BMS, a LiFePO4-specific 8S board (Shenzhen Bozhi BZ808-5080-030C30-B-F-8S, 8S 30A, common port, balancing, temperature control); tidy the harness in order and solder it to the matching tabs.

   01:22 – 01:42
6. 
   6. 16 cells shaped flat to fit the battery bay; charge / discharge test

   With the BMS on, the pack has 16 cells; shaped very flat to suit the battery bay; finally a charge / discharge test.

   01:42 – 01:57

Bill of materials

Creator’s tips

• UF20B welding 0.2 nickel-plated strip onto 32140: gear 30 is easy; 3 welds per cell, 6 spots, to assure current capacity 01:02
• Count LiFePO4 series at 3.65V per cell: 24V → 8S 00:14
• Fish paper on the positive ends, top and bottom holders locked on, gaps between cells help insulation and cooling 00:32
• Design the layout (flat) around the battery bay dimensions 01:48

Pitfalls

• Comment: don’t use it on a big delivery e-bike (not enough capacity / rate)

Li-ion safety

• Check every weld spot after welding to catch loose welds 01:16

Quotes