Introduction: Simple Battery Spot Welder

About: I'm a tinkerer and a DIYer. If it can be made rather than bought then I'll always have a go. A lot of the things I make simply can't be bought anyway!

As part of an electric bike project I needed to weld 70 18650 Li-Ion cells together. I could have just bought a battery welder but where's the fun in that? This is my build. Nothing complicated and it didn't need to last too long.

Step 1: Parts List and Tools Needed



  • Screwdrivers
  • Drill
  • Soldering iron (60W+)
  • Solder

Step 2: Wiring Diagram

This is the circuit we're going to make.

The timer relay can be set to be closed for 0.15s when the button is pushed. This in turn fires the starter solenoid, which allows current to flow down the electrodes, creating the weld.

We could do without the timer relay and just control the weld by varying the time we press the button for but it gives a lot more control.

Step 3: A Solid Base

We don't want the battery floating around the workbench so we need to construct a solid base for it.

Take some 3/4" MDF board and cut it to be 4" wider than the battery and about 4 times as long to give a good welding area in front of the machine.

Cut some 1" x 2" wood and screw it to the board to form the area where the battery will sit.

Step 4: Mount for the Button

Add some more 1" x 2" on the top of the enclosure we just made and cut a hole in it the same diameter as our firing button.

Step 5: Mount the Button

Mount your button in the hole we just made and feed the wires out of the bottom.

Step 6: Test Your Circuit

Wire everything together as shown in the previous wiring diagram and test fire it, making sure that both the relay and the solenoid fire as expected.

Step 7: Mount the Solenoid

We don't want the solenoid floating around so take some of the 10mm x 2mm steel bar and drill 2 holes in it. This will serve as both the positive contact and a solid mount.

Step 8: Electrodes

Take two of the copper nails and cut the heads off them. These will be inserted in to the choc-block to form the electrodes.

Step 9: Main Wires

Cut down some of the copper cable and mount some choc-block on the end. Insert the copper nails in to the other end and bend the wires until the electrodes are vertical and the wires are horizontal.

Screw one wire to the -ve terminal of the battery and the other to the output of the starter solenoid.

Step 10: Test

Grab a battery you don't care about and test it.

You will need to experiment with how much pressure to apply to the electrodes but with a little practice you will be able to do a consistent weld.

I used this welder to build the battery for my electric bicycle: