Homemade jump starter, DIY car emergency power — turning a bought Bluetooth speaker shell into a car jump pack

Bluetooth speaker shell to car jump starter (part 1): 12 × 2500mAh cells in 3P4S, AWithZ welder on auto fires 0.5 s after contact, insulating paper on the negative-can side against shorts, 16.01V after welding; lead-acid tester reads 12.6mΩ / CCA 264; three layers of nickel strip still weld through — ‘a hundred-odd yuan to buy one beats building it’

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).

Outcome

Steps8 steps · click a frame to jump

1. 
   1. Shell, cells, charging board; home-made welder no good

   Solar Bluetooth speaker shell; cells around 2500; Type-C 5V charging board, + to −; a spot welder made from a microwave transformer before was hard work with poor results.

   00:00 – 00:40
2. 
   2. AWithZ spot welder: a hundred-odd yuan, nickel strip included

   Picked up an AWithZ spot welder, one charge lasts a long time, a hundred-odd yuan, bigger discount when it was 168; comes with small nickel strips.

   00:40 – 00:54
3. 
   3. Insulating paper on the negative-can side against shorts

   Before welding, stick on small insulating paper: one side is the negative can, the other the positive; overheating would short them, the paper prevents it.

   00:54 – 01:08
4. 
   4. 3P4S; auto mode fires in 0.5 s; leave some slack

   Grouped 3P4S; touch the welder on and it welds by itself, auto mode fires 0.5 s after contact; weld one end first and press down; welds are clean and solid; the middle isn’t welded too tight, leaving a safety margin; foolproof and handy.

   01:08 – 02:08
5. 
   5. Charge still full after all positives; weld the negatives

   After welding all the positives the charge is still full — small but welds a lot, better than the big home-made unit; on to the negatives, rock solid with a little slack.

   02:12 – 02:39
6. 
   6. Series in pairs, main + and main −

   With the 3P groups welded, join them in pairs, flip and join again; cut short pieces of nickel strip and line them up; mark the main − and main + once linked.

   02:42 – 03:22
7. 
   7. 16.01V; lead-acid tester 12.6mΩ / 13.9V / CCA 264

   DC 16.01V, just right for jump starting; a lead-acid battery tester makes do: resistance 12.6, voltage 13.9, discharge 264, should start a 2.0T car; main + and − still need a few extra wires to raise discharge current.

   03:23 – 04:07
8. 
   8. Two- and three-layer nickel strip test; buying beats building

   Two and three layers stacked both weld on solid; a hundred-odd yuan to buy one beats building it, it’s in the shop window.

   04:12 – 04:37

Bill of materials

Measured on camera

Creator’s tips

• Before welding, stick insulating paper on the negative-can side to stop overheating causing a short 00:54
• On auto it fires 0.5 s after contact; weld one end first and press down 01:24
• Leave a line in the weld and a swollen cell will thank you: leave some slack in the middle 01:54
• For series, join in pairs, then flip and join again; line up the nickel strip pieces 02:42

Pitfalls

• A home-made microwave-transformer spot welder is hard work with poor results 00:26
• The lead-acid tester clips won’t grip and it’s imprecise on Li-ion 03:37
• Comment: no copper strip for a jump starter, and the cells can barely do 2C (creator agrees it’ll do)

Li-ion safety

• Overheating the + and − cans shorts them easily — insulating paper is a must 00:54
• Comment: jump starting draws huge current; nickel strip / cells without the C-rating are a risk

Quotes

Cost & time