Extreme Current Manipulation: DIY CD Spot Welder

Building custom 18650 LiPo battery packs for e-bikes or robots requires bonding nickel strips directly to the battery terminals. You cannot use a soldering iron; the sustained heat will literally cause the lithium battery to explode. The DIY Spot Welder utilizes an Arduino to generate an incredibly precise, 20-millisecond pulse of massively destructive electrical current, fusing the metals instantly before the battery cell even has time to get warm.

The Physics of Resistance Welding

An Arduino cannot output 500 Amps. It must act as the orchestrator of a far more terrifying power source: A modified Microwave Oven Transformer (MOT).

1. A hacker carefully rips the thin, high-voltage secondary coil out of a dead microwave transformer.
2. They replace it with exactly 2 to 3 winds of incredibly massive, thumb-thick welding cable.
3. This "step-down" modification drops the 110V/220V wall power down to a harmless 2 Volts, but amplifies the current to an astronomical 800 to 1000 Amps!
4. When you push those two copper cables against a nickel strip against a battery, the 800 Amps try to force their way through the tiny connection point. The massive electrical resistance causes the nickel to instantly melt into a white-hot puddle of plasma for a fraction of a second, fusing the metals!

The Solid-State Microsecond Timer

If the 800A current flows for 0.01 seconds, you get a perfect weld. If it flows for 0.05 seconds, it blows a hole straight through the battery and starts a lithium fire.

• You cannot use a mechanical relay to control the transformer! Relays "bounce" and stick, leading to disaster.
• The Arduino commands a massive BTA100 or BTA41 TRIAC (A solid-state AC switch) or a massive bank of MOSFETs if using DC supercapacitors.
• The Code Loop:
  • The user sets a rotary encoder to "25ms".
  • The user presses the foot pedal.
  • digitalWrite(TRIAC_PIN, HIGH); delay(25); digitalWrite(TRIAC_PIN, LOW);
  • The Arduino executes the blast perfectly, stopping the flow of power with absolute mathematical precision that a human hand could never replicate.

Heavy Duty Fabrication Parts

• Arduino Nano (To run the OLED timing screen and rotary encoder dial).
• A Salvaged Microwave Oven Transformer (MOT) or a massive bank of 3000 Farad Super Capacitors (CD - Capacitive Discharge setup).
• Solid State TRIAC Board (AC) or massive MOSFET Bank (DC).
• Heavy welding cables and solid copper welding electrodes.
• (DANGER: This project manipulates lethal AC mains voltages and near-explosive capacitor banks. Absolute caution, thick rubber gloves, and extreme protective eyewear are non-negotiable!)