DIY Plug-and-Play Spot Welder | Powered by a Multipurpose LiPo Battery (No Special Wiring Needed!)

A dedicated spot welder strong enough to weld nickel strips onto 18650/21700 cells typically costs around ₹7,000 (~$74 USD) in the market. As someone who builds robots, drones, and battery packs for my own projects, I needed one — but not badly enough to spend that kind of money on a tool I'd use occasionally.

So instead, I built my own for about 1,500 (~$16 USD) using a ready-made capacitor-discharge spot welder module — and powered it with a 3S LiPo battery I already own and use for other things (robot power, flight packs, day-to-day experiments). Rather than locking that battery into one single-purpose tool, I wired everything with XT60 connectors on both ends, so the same battery simply plugs into whichever project needs it — spot welder today, robot or drone tomorrow.

This is really the heart of the project: it's not just "a battery-powered spot welder," it's a reusable, multipurpose battery setup where the spot welder is just one of several plug-and-play loads it can power. The wiring itself stays dead simple — battery in, probes out — which makes this an approachable build even if you're not deeply into electronics.

Why I Built It This Way

1. Cost-effective vs. buying a dedicated welder: (~$16)~₹1,500 for the welder module + parts, vs. ~₹7,000 (~$74) for a commercial unit.
2. No battery locked into one tool: My 3S 3300mAh 35C (70C burst) LiPo isn't dedicated to this welder — I use it across robotics, flight, and general experiments. It only becomes "the spot welder's battery" for the few minutes I'm actually welding.
3. True plug-and-play: XT60 connectors on the battery side and matching connectors mean I can unplug the battery from the welder and plug it straight into another project with zero rewiring.
4. Personal/practical need: I regularly spot-weld 18650/21700 cells for my own battery packs, so this tool directly serves my day-to-day build requirements — it's not a one-off novelty.

If you only count the welder module and parts, the real incremental cost of "adding spot welding" to my toolkit was about (~$16)~₹1,500 — the battery cost (~₹2,500 / ~$26) is shared across many other projects, not spent specifically for this.

1. spot welder module kit (module + welding rods/probes + 12AWG wires + connectors + mounting screws) — ₹1,250 (~$13)
2. XT60 connector pair (battery side) — ₹30 (~$0.32)
3. XT60 connector pair (probe/output side) — ₹30 (~$0.32)
4. Handmade PVC enclosure box + spray paint — ₹100 (~$1)
5. Extra pushbutton switch (for external trigger mod) — included in general parts

Total spend on the welder itself: ≈ ₹1,500 (~$16)

1. 3S 3300mAh 35C (70C burst) LiPo battery — ₹2,500 (~$26) (already owned — multipurpose battery used across robotics/drone/experiments, not bought specifically for this build; shared cost, not counted against this project)

Effective project cost: ~₹1,500 (~$16) — the battery is a reusable asset, not a dedicated expense for the welder.

1. IN+ / IN− — battery connects here, powering the onboard capacitor bank.
2. OUT+ / OUT− — welding probes connect here; stored energy discharges through these terminals.
3. Large capacitor — stores energy between welds.
4. 5x MOSFETs — switch the stored energy into a sudden high-current pulse through the probes.
5. Onboard mode-selection switch — the module ships with a built-in switch for trigger/mode control.
6. Buzzer — beeps to indicate the capacitor is ready to fire.

It's a self-contained analog charge/discharge board — no programming involved, just input/output wiring.

The module comes with a built-in mode-selection/trigger switch directly on the board. Operating that switch from inside a closed enclosure isn't practical, so I rerouted it to the outside:

1. Identify the 4 solder pins/pads connected to the module's onboard switch.
2. Desolder the onboard switch (or simply leave it unpopulated if it's not yet soldered).
3. Solder 4 wires onto those same 4 pads.
4. Solder the other ends of those 4 wires onto an identical external pushbutton switch (same type/rating as the original).
5. Mount this external switch on the outside of your enclosure.

This gives you full control of triggering from outside the closed box, without modifying any of the welder's core circuitry — just relocating the same switch to a more convenient spot.

1. Use the 12AWG wires included in the kit (red/black) for the probe leads.
2. Solder the supplied copper welding rods onto the working ends.
3. Slide heat shrink tubing over each solder joint and shrink it for insulation and strain relief.
4. The other ends will connect to the board's OUT+ / OUT− terminals (see Step 5).

Shorter, lower-resistance probes give a cleaner, more concentrated weld.

This is the key step that makes the whole project "plug and play":

1. Battery side: Solder an XT60 male connector to the wires going to IN+ / IN− on the board. Your multipurpose LiPo already has (or gets) a matching XT60 female connector — so it can be plugged into the welder, then unplugged and used on another project in seconds.
2. Probe side: Solder a second XT60 pair between the board's OUT+ / OUT so the probes themselves are also detachable from the board if needed.
3. Two XT60 pairs total — one for power in, one for probes out. No soldering required at the point of use; everything is connector-based.

1. Build/cut your PVC enclosure to size and spray paint it (mine cost ~₹100 total for the box and paint).
2. Drill mounting holes and screw the module down securely using the screws included in the kit — OUT+/OUT− carry high current, so keep these connections mechanically solid.
3. Cut openings for the battery-side XT60 connector, the probe wires, and the external trigger switch from Step 2.
4. Route and mount the external pushbutton switch from Step 2 to an accessible spot on the box.
5. Close up the enclosure, leaving the battery connector, probes, and trigger switch accessible from outside.

1. Plug your 3S LiPo into the welder's battery-side XT60 connector.
2. Let the capacitor charge — listen for the buzzer/ready indicator.
3. Touch both probe tips onto your test piece (18650/21700 cell tab, nickel strip, sheet metal, etc.) and press the external trigger button.
4. You'll see a quick, intense spark as the stored energy discharges through the joint — that's your weld.
5. Tug-test the joint for strength; adjust probe pressure/contact and repeat as needed.
6. When done, unplug the battery and use it for whatever's next on your bench — robot, drone, or another experiment.

⚠️ Safety Notes

1. High-C LiPo batteries can deliver very large short-circuit currents — never let the probe tips or battery terminals touch each other accidentally.
2. Wear eye protection — there is real spark/spatter during welding.
3. Work on a non-flammable surface, away from anything combustible.
4. Unplug the battery when not actively welding.
5. Handle and store the LiPo per normal LiPo safety practices (no punctures, no extreme heat, no short circuits).

The result: a fully portable spot welder that cost me about ₹1,500 (~$16) to build (instead of ~₹7,000 / ~$74 for a commercial unit), powered by a LiPo battery that isn't locked into this one tool — it's the same battery I plug into my robots, flight packs, and other experiments. When I need to spot-weld a battery pack, I plug it in here; the rest of the time, it's back in service elsewhere.

Possible upgrades for next time:

1. Add a foot-pedal trigger for fully hands-free operation
2. Add an adjustable pulse-duration/timer circuit for finer weld control
3. Add a simple voltage indicator on the enclosure so I know the battery's state before welding

📺 Watch the full build video here:DIY Plug-and-Play Spot Welder | Powered by a Multipurpose LiPo Battery (No Special Wiring Needed!)

This project isn't just "a spot welder" — it's proof that a single multipurpose battery, paired with the right plug-and-play connectors, can serve many roles instead of being dedicated to one. For about a fifth of the cost of a commercial spot welder, I now have a tool that handles my actual day-to-day need (welding 18650/21700 packs), while the battery itself stays free to power whatever else I'm building next.

Entered in the Battery Powered Contest.