Spot Welder for Lithium-ion 18650 Battery Tutorial




Intro: 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


    6 months ago

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

    3 replies

    Reply 8 weeks 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 5 months ago

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


    8 weeks 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.


    6 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 6 months ago

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


    Reply 6 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.


    7 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?


    1 year 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.