Editing Battery Refurbishment (section)

== Step 11: Spot weld ==

=== Calibrate on scrap first ===

'''Never start on your real cells.'''<ref name="mc-weld" />

# Set the machine to roughly '''50 % of its capacity'''.
# Weld a piece of '''your actual strip''' to a scrap or dead cell.
# '''Pull test it.''' If the strip peels off cleanly, raise the power by 10–15 % and repeat.
# Continue until the pull test passes — the strip tears rather than the weld letting go.
# Push slightly higher until you see burn-through or discolouration of the terminal; the setting below that is your maximum.
# '''Your working range is: passes the pull test, without burning through.''' Write the setting down against the strip gauge, strip material and cell type. Recalibrate when any of those changes.

Calibration takes fifteen or twenty minutes and it is the difference between a pack that lasts and a pack that comes apart.

=== Technique ===

* '''Electrode spacing: 2–5 mm.''' Too close (under 2 mm) and the current takes the short path through the strip surface instead of down through the interface, leaving shallow welds. Too far (over 7 mm) and the energy is dissipated heating the strip instead of the joint. Use the closer end of the range for 0.1 mm strip and the wider end for 0.2 mm.<ref name="mc-weld" />
* '''Pressure: firm and steady.''' Enough that the electrodes cannot be slid sideways without lifting them; not so much that the strip deforms before the pulse fires. Too little pressure causes surface arcing and sparks with poor penetration below; too much deforms the strip and risks slipping.<ref name="mc-weld" />
* '''Hold the electrodes vertical''', press, and trigger without hesitating — hesitation lets the pressure waver.
* '''Maintain pressure for about half a second to a second after the pulse''' while the nugget solidifies, then lift cleanly. Do not lift immediately, and do not drag the electrodes sideways.
* '''Two weld spots minimum per strip end per terminal''', four for anything carrying real current. Keep the spot positions consistent from cell to cell.
* '''Work methodically''' along the strip from one end to the other. Finish one cell before moving on.
* '''On the positive end''', the strip contacts the raised button; the slight offset is normal and the weld still forms at the button interface.

=== Check the welds ===

'''Visual.''' A good weld leaves '''two small, clean, round indentations''' of consistent size where the electrode tips sat. Slight darkening is normal. Elongated, smeared or asymmetric marks mean the pressure or position wavered; sparking marks away from the intended spots, visible holes, or discolouration of the cell terminal all mean too much energy.<ref name="mc-weld" />

'''Pull test.''' The definitive check: grip the strip with pliers and pull it straight away from the terminal. '''A good weld tears the nickel and leaves a fused remnant on the cell.''' A bad weld peels off cleanly leaving the terminal essentially unmarked. Do this destructively on your scrap during calibration, not on every production weld.<ref name="mc-weld" />

'''Resistance.''' A well-made nickel tab weld measures roughly '''0.05–0.3 mΩ'''. Higher means a cold weld, oxide contamination or misalignment. This needs a milliohm meter, which is optional for a one-off job but the only quantitative measure available.<ref name="mc-weld" />

=== Weld fault table ===

{| class="wikitable styled-table" style="width:100%; text-align:left;"
|+'''Spot welding faults and cures'''<ref name="mc-weld" />
! Symptom !! Likely causes !! Fix
|-
| '''Strip peels off cleanly on the pull test''', minimal mark on the terminal || Power too low; dirty or worn electrode tips; not enough pressure; electrodes too close together; strip not flat against the terminal || Check and dress the electrodes first, confirm the strip is flat, then raise power in 10 % steps
|-
| '''Holes burnt through the strip'''; terminal discoloured || Power too high; electrode tips too sharp; electrodes too close together || Reduce power; use a slightly blunter tip radius; widen the spacing a little
|-
| '''Weld spots vary in size and depth''' at a fixed setting || Worn electrodes; inconsistent hand pressure; strip not consistently flat; varying surface oxide || Dress the tips, practise consistent pressure on scrap, consider a dual-pulse machine
|-
| '''Electrodes stick to the strip''' || Power too high; nickel contamination on the tip; tip too pointed || Reduce power; clean and reshape the tip; increase the tip radius slightly
|-
| '''Lots of sparking at the tips''' || Insufficient pressure; oxidised strip surface || Press harder; clean the strip; use dual pulse if available
|}