Simple Battery Spot Welder

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.

Parts:

• Momentary push button
• Car starter solenoid
• Copper nails
• Heavy-duty cable
• 60A choc-block
• Timer relay circuit
• 3/4" MDF board
• 1" x 2" pine batten
• 10mm x 2mm steel bar

Tools:

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

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.

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.

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.

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

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.

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.

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.

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.

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: https://www.instructables.com/id/Convert-a-Full-suspension-MTB-in-to-a-Go-anywhere-/