Spot Welder for Lithium-ion 18650 Battery Tutorial




Easy to build DIY spot welder for under 60$.
Works great und safes a lot of time.

High temperature destroys lithium batteries, so soldering is no option.

I want to build a 700Wh battery pack for my electric homemade boat and E-bike using 60 panasonic ncr18650b lithium batteries.

Step 1: Watch the Video! Check Schematics for the List of Material

Thats all you need:

1 x resistor 1k

1 x resistor 10k

1 x foot switch

1 x Hifi Cap min. 1F

8 x MOSFET IRF1404

1m copper cable 2.5mm²

2m copper cable 35mm²

Copper rails

Total costs: about 60$

Step 2: Attach the MOSFETs and the Eyelets to the Copper Rails

Sand the copper rails for better

The eyelets are very easy to bend (watch the video)

Step 3: Wooden Base Plate and Copper Clamps

Attach the Hifi Cap to the wooden base plate.

Make the copper clamps for the 35mm² cable and the cap.

Use wodden distance plates to attach the copper rails with the FETs and eyelets.

Step 4: Solder GATE and SOURCE Pins

Solder eyelets to the SOUCE pins of the FETs.

Connect all GATE pins.

Dont´t foreget 10k resistor between GATE and SOURCE

and 1k resistor after the foot switch.

Step 5: Welding Cables and Connector

Connect one 35mm² welding cables to the plus pole oft he cap

and the second to the DRAIN copper rail.

I also installed a connector for the battery and the foot switch.

Step 6: Welding Tips

Use for the welding tips the 2.5mm² copper cable.

Stick the 2.5mm² copper cable into the 35mm² cable as shown in the video.

Now you are ready to do your first welding tests.

To load the Cap use a power supply or a 12V battery with a 60W lamp in series.

Benefit of the power supply: you can vary the amount of energy in the cap.

Have fun!



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    11 Discussions


    10 months ago

    What would be a good way to protect the MOSFETs? After a couple test welds, all of them fried :(

    3 replies

    Reply 6 months ago

    Much better to use a $2 motorbike starter relay (eBay)... although rated at 80A they can handle 1000A no problem if in a short pulse ... I've used one for 1000's of welds


    Reply 10 months ago

    thats sad to hear! were the mosfets hot to the touch or did they just blow directly?


    6 months ago

    Really no need for that expensive capacitor with the necessity of waiting for it to charge up each time ... a slightly bigger lithium pack will deliver enough current and can be used on its own ... or any 12V car battery.... vary the length /thickness of the cable to set the current to the right level ...once set , no need to change again.


    11 months ago

    I've built one! I assembled the parts around the cap with 3D printed parts. I also built an Arduino powered relay switch just to make sure that the pedal presses are consistently the same 100ms. Thank you for the tips!

    2 replies

    Reply 11 months ago

    Hi, it would be nice if you showed us what components you used. Thanks


    Reply 11 months ago

    The cap is a "2F" (more like .5F) from Boss Audio. Got it from Amazon for like $33. I used 10x IRF1404 just because I had 10. Got them from Aliexpress for around $2 for 10pcs. Two 18650 cells in series used for the switching of the mosfets. Copper rails from Aliexpress. 2AWG Battery charging cables from Amazon. Arduino Nano with a 5V relay to turn the mosfets on/off at a consistent length of time. I'm still dialing it in.


    12 months ago

    Do you have to watch how long the step switch is pressed down - or does it just drain all the current from the cap so there's only one pulse and that's it? What would happen if you held the pedal down?


    2 years ago

    Thanks for your tip


    2 years ago

    Looks good! Just for reference if you would like to break down the steps into written instructions and add some progress/step photos so that others can replicate your projects then it will receive more attention from the community and be possible to be featured on the site.