Ever wanted to build custom battery packs for electric bikes, solar power banks, or RC projects but found commercial spot welders too expensive? I've got the perfect solution! In this Instructable, I'll show you how to build a powerful yet affordable battery spot welder from scratch. This isn't just another simple project—it's a professional-grade tool that uses the classic NE555 timer and parallel MOSFETs to deliver precise, controlled welding pulses.

that makes this design special is its intelligent balance between simplicity and functionality. While commercial welders can cost hundreds of dollars, this DIY version achieves similar results at a fraction of the price. The secret lies in the carefully designed circuit that transforms a standard 12V battery into a controlled high-current welding machine. Whether you're assembling a power wall for home energy storage or building custom packs for your electric skateboard, this spot welder will become an indispensable tool in your workshop.

I've personally used this welder to assemble multiple battery packs, and I can vouch for its reliability and effectiveness. The design focuses on safety first, with controlled pulse timing that prevents battery damage and ensures consistent welds every time. Let's dive in and build something amazing!

Supplies

You'll need electronic components, basic tools, and some raw materials for this project. For the main circuit, gather an NE555 timer IC, six IRLB4132 MOSFETs, several resistors (10kΩ and 220Ω values), capacitors (100nF and 100μF), a 5mm LED, a momentary push button, and a piece of prototype PCB or a custom-designed board. You'll also need a 12V battery—a 7Ah sealed lead-acid battery works well to start, though you can upgrade to higher-capacity batteries later.

For the welding probes, source two pieces of 4mm solid copper rod, thick insulated copper cables (at least 12 AWG), heat shrink tubing in various sizes, and a small plastic enclosure or handle material. Basic tools include a soldering iron with solder, wire cutters, a multimeter, a drill with bits, and a screwdriver set. Optional but helpful are a PCB holder, helping hands, and safety equipment like gloves and safety glasses.

Schematic and PCB Design

Begin by creating the circuit schematic. The heart of our spot welder is the NE555 timer configured in monostable mode. This generates a precise 10ms pulse when triggered. Connect the NE555 following standard monostable configuration: pin 1 to ground, pin 8 to VCC, with a 10kΩ resistor between pins 7 and 8, and a 100nF capacitor from pin 6 to ground. Connect pin 2 (trigger) through a 10kΩ pull-up resistor to VCC and to one side of your push button the other button side goes to ground.

Circuit Schematic.png

The output from pin 3 drives the gate of our MOSFET array. Since a single MOSFET can't handle the hundreds of amps needed for welding, we'll use six IRLB4132 MOSFETs in parallel. Connect all gates together, all sources together, and all drains together. Add a 220Ω resistor in series with an LED from pin 3 to ground as a pulse indicator. Finally, connect the MOSFET sources to ground and the drains to the positive welding probe terminal.

PCB 3D Render.png

For the PCB, design wide traces at least 3mm for all high-current paths. Remember that thinner traces will overheat during welding pulses. Arrange components logically with the NE555 and support components on one side and the parallel MOSFETs with ample spacing for heat dissipation on the other. Include clearly labeled terminals for battery input, welding probes, and trigger switch. Once satisfied, export your design as Gerber files for manufacturing. I used JLCPCB, where all solder mask colors cost the same, so pick your favorite!

Circuit Assembly

With your PCB in hand, start assembling components from smallest to largest. First, solder the resistors and capacitors. Use an IC socket for the NE555—this protects the chip from soldering heat and...

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