Building a car jump-starter power bank from 8 tabless Ampace JP40 cells

Hand-Built Bro’s 8-cell car jump starter: Ampace JP40 tabless 21700 (20C) in 2P4S, max ‘32000’ capacity, held in a holder with fish paper on the positives, stacked spot welds of 0.15 copper + 0.15 nickel-plated steel strip (main + / − use a long copper strip + two nickel squares), marked B-/B1/B2/B3/B+ to a 4S BMS (thin white wires + 16 AWG silicone wire), EC5 jump-start port, XT30 to a PD100W module, needs a charge to wake up the first time you press it, finished at 14.2V

By viewer request, an 8-cell car jump starter. Cells are Ampace tabless 21700s, 20C burst discharge; layout two parallel, four series, max ‘32000’ (mAh) capacity. Cells fixed in a holder as 2P4S: the first series group two cells positive-up in the slots, the second group negative… (these were unpacked for an earlier video but are still brand new); fish paper on the positives; spot-weld in series with stacked copper: 0.15 copper on one side, 0.15 nickel-plated steel strip stacked on the other. Copper and nickel pre-cut; first weld the main + / − outputs: a slightly longer copper strip + two nickel squares, lay the copper first, then the nickel-plated steel on top, spot weld; the negative the same way; the upper part is welded across; flip and weld lengthwise (a layer of copper, a layer of nickel), note two places must not connect; + and − don’t need to connect anywhere else, follow the plan and it is correct. Mark positions with a marker: B- main negative, B+ main positive, B1, B2, B3; matching pads on the BMS: thin white wire for B1/B2/B3, thicker 16 AWG silicone wire for B+/B-. Into the box (a layer of white silicone rubber if you can); the EC5 connector is soldered to the two copper strips (rounded, full joints) and covered with heat-shrink; XT30 on the BMS P+/P- for easy connection to the PD module; EC5 screwed down, lower battery section done. The top cover takes the PD100W module on self-tapping screws; wiring done, the thin copper wire is the temperature sensor, place it anywhere; XT30 male-female plugged together. If nothing happens when you press it, don’t panic, charge it with the charger to wake it up. Case screwed on; EC5 for car jump starts, power-bank functions on top with two C ports and two A ports, voltmeter 14.2V, display shows 22% charge. Comments: will 18650 do; can it start a 2.5T; safe to leave in the car long-term; how many starts from 4000 capacity; is it 14V assembled; welder recommendation please.

Outcome

Steps10 steps · click a frame to jump

1. 
   1. Plan: Ampace tabless 21700 20C, 2P4S, 32000

   8-cell jump starter; Ampace tabless 21700, 20C burst; two parallel, four series; max 32000 capacity.

   00:00 – 00:17
2. 
   2. Holder as 2P4S, fish paper on the positives

   Cells fixed in the holder as 2P4S; first series group positive-up in the slots, second group negative; the cells were unpacked before and are brand new; clip the holder on; fish paper on the positives.

   00:17 – 00:53
3. 
   3. Stacked copper welds: 0.15 copper + 0.15 nickel-plated steel strip

   Spot-weld in series; stacked copper welding, 0.15 copper on one side and 0.15 nickel-plated steel strip stacked on the other; copper and nickel pre-cut.

   00:53 – 01:10
4. 
   4. Weld the main + / − outputs first (long copper + two nickel squares), then the upper part across

   Main + / − outputs use a slightly longer copper strip + two nickel squares; lay the copper first, then the nickel-plated steel, spot weld; negative the same; the upper part is welded across.

   01:09 – 01:49
5. 
   5. Flip and weld lengthwise; watch the places that must not connect; mark the B-wire positions

   The other side is welded lengthwise, a layer of copper and a layer of nickel; note here and here must not connect; + and − don’t connect anywhere else; mark the BMS wire positions with a marker.

   01:53 – 02:30
6. 
   6. B-/B+/B1/B2/B3 definitions and BMS mapping

   B- main negative, B+ main positive, one down from B- is B1, above it B2, the other is B3; the BMS has B1 B2 B3 and B+ B-, wire them to match.

   02:30 – 03:01
7. 
   7. Solder the sense wires: thin white for B1/B2/B3, 16 AWG silicone for B+/B-

   B1 white wire soldered to the pad and run to the marked spot; B2 soldered above; B3; three thin white wires; B+/B- use the thicker 16 AWG silicone wire.

   03:07 – 03:58
8. 
   8. Into the box; EC5 soldered to the copper with heat-shrink; XT30 on P+/P-

   Into the box (white silicone rubber optional); check the EC5 position; EC5 soldered to the two copper strips with rounded, full joints, covered in heat-shrink; XT30 on the BMS P+/P- for easy connection to the PD module; EC5 screwed down.

   03:58 – 05:14
9. 
   9. PD100W module on the top cover; temperature sensor; charge to wake up

   PD100W module fixed with self-tapping screws; wiring done; the thin copper wire is the temperature sensor, place it anywhere; XT30 male-female plugged together; if nothing happens when pressed, don’t panic, charge it with the charger to wake it up.

   05:14 – 06:06
10. 
    10. Finished: EC5 jump start + 2C2A power bank, 14.2V 22%

    Case screwed on; EC5 for car jump starts; two C ports and two A ports for charging; voltmeter 14.2V, display shows 22%; good fun to build one yourself.

    06:06 – 06:28

Bill of materials

Measured on camera

Creator’s tips

• Stacking order: lay the copper first, then the nickel-plated steel, then spot weld 01:22
• Main + / − outputs use a long copper strip + two nickel squares to carry the jump-start current 01:09
• Mark the B-wire positions with a marker before welding; thin wire for B1–B3, thick for B+/B- 02:17
• XT30 on P+/P- makes hooking up the PD module easy 04:59
• If the button does nothing after assembly, charge it first to wake it up 05:53
• EC5 joints should be rounded and full, and covered with heat-shrink 04:47

Pitfalls

• When welding lengthwise on the other side there are two places that must not connect; get it wrong and it shorts 02:06
• Nothing happens on the first press (BMS asleep) 05:53

Li-ion safety

• Fish paper on the positives for insulation 00:40
• Comment: any safety issue leaving it in the car long-term (unanswered)

Quotes