Back then I was a newborn calf that feared no tiger and nothing ever went wrong; now on the third build I keep ‘blowing it up, bro’ — mainly my own carelessness, but this AWithZ P60F welding pen is longer than the old UF20B one, which gave me two shorts and blackened the pen; if I use it again I’ll wrap it in high-temperature tape, whether it needs cooling or not

Lefeng ‘blowing it up, bro’ round three: the P60F pen is longer than the UF20B’s and not fully enclosed (has a gap), so while welding the main negative it touched a positive / another strip — bang, two shorts, blackened pen, cable ripped off; nickel strip edges cut his hand; the 50A copper lugs for main +/− were too thick, so switched to screw terminals with heat-shrink; the positive red lead must never be swapped; remedy: high-temperature glue + cutting paper + fireproof board over the pen gap, main +/− sealed with 704 silicone, fiber tape, then solder the sense harness; comments: sleeve the pen in nylon braid / polyimide film, same pen blew through a 50 mm² welding cable

Straight short, ‘blew it up, bro’, cotton swab from the bag to wipe his hand — just got cut by the nickel strip again, the welding pen touched the strip and blew twice; the corner of the strip went in and it ‘burst like tomato juice’, this build really wrecks your hands. The 50A copper lug connected and a dab of solder on it; meant to spot-weld it onto the copper plate but found the lug too thick, so back to the old way, screw it, heat-shrink over it, onto the copper plate, then spot-weld to the main positive and negative; when soldering the leads the positive must go to the red positive, get it wrong and it blows up again. Nearly blew it up again just now: welding the main negative, this pen isn’t fully wrapped, it has a gap, the gap touched a positive, bang, the cable was ripped straight off, terrifying, the cable feels unsafely designed — not fully enclosed, and yes enclosing it hurts cooling, but I keep touching other things, clip another strip and it blows; same recipe as before: high-temperature glue, then cutting paper, then a layer of fireproof board on top, this corner is the blackened spot; the short blew right at the pen; this time the main +/− get sealed with 704 silicone first, then a few turns of fiber tape and the sense harness can be soldered. Comments (116): sleeve the pen in nylon braided mesh (noted); my pen is identical and it blew straight through the 50 mm² welding cable, only a few strands left (that bad?); wrap it in polyimide film; no BMS? not on LiFePO4?; solder the main +/− straight onto the copper plate (I prefer screws); safety first (scared stiff); running deliveries in Changsha.

Outcome

Steps5 steps · click a frame to jump

1. 
   1. Two shorts, ‘blew it up’; nickel strip cut his hand, ‘tomato juice’

   Straight short, blew it up, bro; cotton swab on the hand; cut by the nickel strip again; the pen touched the strip and blew twice; the strip corner went in and burst like tomato juice, this build wrecks your hands.

   00:01 – 00:27
2. 
   2. 50A lug too thick to spot-weld, switched to screw terminals with heat-shrink onto the copper plate, then spot-welded to main +/−

   50A copper lug connected with a dab of solder; meant to spot-weld onto the copper plate, lug too thick; old way, screw it; heat-shrink over it onto the copper plate, then spot-weld to the main positive and negative.

   00:27 – 00:52
3. 
   3. The positive red lead must never be swapped

   Soldering these two leads, positive must go to positive (red); wire it out wrong and it blows up again.

   00:52 – 01:06
4. 
   4. Third time: the P60F pen’s gap touched a positive, bang, cable ripped off, unsafe design

   Welding the main negative, the pen isn’t fully wrapped and has a gap, the gap touched a positive, bang, the cable was ripped straight off, terrifying; the cable design is unsafe, not fully enclosed (enclosing hurts cooling), it keeps touching other things, clip another strip and it blows.

   01:06 – 01:45
5. 
   5. Hardening: high-temperature glue + cutting paper + fireproof board; 704 silicone on main +/−; fiber tape, then the harness

   Same recipe as before, high-temperature glue, then cutting paper, then a layer of fireproof board; this corner is the blackened spot, the short blew at the pen; main +/− sealed with 704 silicone first; then a few turns of fiber tape and the sense harness can be soldered.

   01:45 – 02:24

Bill of materials

Creator’s tips

• The pen isn’t fully enclosed and has a gap; on a big pack the gap touches a positive and shorts — sleeve the pen in braided mesh / polyimide film / high-temperature tape (comments + creator) 01:06
• If the copper lug is too thick to spot-weld, use screw terminals with heat-shrink and then attach to the copper plate 00:27
• Seal main +/− with 704 silicone and wrap with fiber tape first, then solder the sense harness 01:59
• The positive red lead must not be swapped 00:52

Pitfalls

• Third pack build and still two shorts, blackened pen and a ripped-off cable 00:01
• Nickel strip edges cut his hand and drew blood 00:01
• Comments: the same pen blew through a 50 mm² welding cable

Li-ion safety

• The pen gap touching a positive means an instant short and a blown cable, extremely dangerous; insulate the pen, deburr strip edges, wear gloves 01:06
• Comments: a big LiFePO4 pack with no BMS?

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