While we work on some projects which involves many 18650 Li-ion cells. For that, we need a Battery Spot Welder. It is expensive but not really difficult to build so in this tutorial we will see how we can make a DIY Battery Spot Welder which is a great tool to have when working on projects.
Disclaimer: Try this project at your own risk, If you have no idea about Mains wiring do not attempt to replicate this project!
Step 1: Transformer Control
First, we need to control the time for which the transformer will be ON. Such that, we can use the high current for the fraction of second to fuse two metal surfaces to achieve welding. For this purpose, we can sue IC555 timer. Since, the voltage is AC and its value is very high, we cannot use IC555. We can use the relays instead, which act as AC switches.
Download Schematic & Gerber files of PCB from here,
Note: We can observe from the circuit diagram that when switch is pressed the Relay 1 will be ON. When the capacitor discharges, Relay 2 will be ON. As capacitor can hold charge for a very short time, Relay 2 will be ON for a very short time. And by the amount of time Relay 2 is ON, we can determine the time of current that will pass through the welding arms.
Step 2: Assembly of the circuit
After receiving the PCBs, we can solder the components in their place. Relays and screw terminals can be soldered. We use screw terminals for ease of changing the capacitor value, if necessary.
Step 3: Make and arm for the spot welder
Then, we extend the output wires of the transformer using 35 sq.mm wires. After that, we take out the skin of wire for about an inch, where we’ll place the 2.5 sq.mm copper wire and fix it in its position, by using electrical tape and hose clip.
By using zip ties along the length of the wire, we can make an arm for the spot welder.
Step 4: Positioning and testing
Position the transformer, the circuit, the battery pack with hot glue. Then, we can test the assembly by adding a switch, connecting supply, and attaching 47 and 100 micro farad capacitors in parallel. And this project will be successfully complete.