Resistive Spot Welder

ByJohn Wuethrich

Resistive Spot Welder

Power Mosfets and a Bank of Maxwell Ultracaps Create a Powerfull Capacitive Discharge Resistive Spot Welder.

Version 1

I set out to build a Resistive Spot welder that could possibly even weld copper. not sure if it will or not as this capacitive discharge welder is back burnnnered at the moment. I wish i had got to test the jig.

this MOSFET switched capacitive discharge resistive spot welder project was intended for my use to allow assembly of quality lithium-ion packs from well-matched cells with reliable cell to cell welds.

Resistive Spot Welder 1

The Cosmic Spot Welder v1

Resistive Spot Welder 2
Cosmos was the namesake for this project. I got him in 8th grade and even though I knew in the back of my mind something was wrong at home, everytime I showed up Cosmos was happy to see me. He was a stray and I made sure he wasn’t an indoor cat. He died in my lap may 2017. 16.5 years old. My regret is the last 4 years I hardly saw him at all. Worse yet my parents claim to own me and have held up everything i put all that time into for over a year in a way that may take my life, heath and or mind. Im sorry Cosmos. I love you.

I didn’t desire to pay the $3000 USD that a sunstone machine runs but I needed something that wouldn’t be a liability for 3 projects i had in the works. Version 1 was still pretty early in for me learning PCB Design. Ill post more on v2 if i ever get out of this hostage situation my parents are enforcing.

Here was programing the pulse duration via rs232 and putty.

Testing a weld to failure

A real weld should fail around the weld nugget. the material around it loses strength due to heating. Its known as the heat effected region. If a weld fails with both parts separating like the originally were then you dont have a weld.

note I got to use this about 20 times. most of it was not blowing holes. I lost a lease due to mold in my parents house transferring to a wet car floor then my apt when Cosmos was sick the last time.

Despite having designed this itteratively and all the switching and smaller circuits tested, my probably cluster b mother whom needed me to make powerpoints for teaching nursing when the overhead went the way of the dodo in 2000 all the sudden knew that none of the projects I was doing had any value… but only after knowing i made up the illness because none of them worked. funny how one can know that but not list the titles? hmm

I rushed to prove this could weld. I was working with one psu and had not yet made the ADC voltage monitor and solid state bank bleed board. I literally charged the bank to full at 16.8v disconnected one bench supply, reset and plugged it into logic. I then trial and error figured out where it ended up making working welds as the voltage dropped in the ultracap bank with each press of the foot pedal. Eventually, i stopped blowing holes.

I was welding nickel tab to nickel tab in anticipation of vaporizing a bit at first.

I wasn’t really expecting the spark. I had a full face respirator on/my eyes were safe, it still caught me off guard so i derp around for a second after 😀

Why Weld Packs Cant I Solder?

A welded cell to cell connection is far less brittle. also lithium-ion cells are very much affected by overheating. A soldering iron is far more likely to heat the entire cell due to longer contact time. weld heat is intense but brief.

Configuration of the welder

Maxwell supercapacitors/Ultra Capcitors in two parallel strings of 6 series for 16.8v max and 116 f

Later as seen above, later an untested 3rd row.

A touch screen was intended. in the video above, i set the timing with rs232 serial and keyboard on the laptop to increment to decrement

Resistive Spot Welder 3
oxidized to all hell.
Resistive Spot Welder 4
Resistive Spot Welder 5
Resistive Spot Welder 6
Resistive Spot Welder 7
Resistive Spot Welder 8

Why Would Somone Make their Own Packs?

China cells or packs featuring cells with fire right in the name seemed like too much truth in advertising and american made either comes with limitations like requiring complicated battery auth with bms or $. So I decided on assemble your own from sourced cells. This isnt meant to be a post on pack construction though. I will probably publish one at some point because a lot of the YouTube community and especially ebike community scares me speechless when it comes to litium ion pack construction.

This is a write up on an early but working design for a CD Spot Welder. Its fet switched and electrically isolated with intent of actually being able to control all electric fab processes. The weld energy comes from a bank of

Resistive Spot Welder 9

The industry standard method (for round cylindrical lithium ion pack construction) is to spot weld nickle or copper between cells. Tesla Motors uses the wire gauge as a fuse, but i dont need anything that fancy yet. Copper would be better but nickle is pretty standard. like the cells or packs, the tool to do this is either $ or China and meh. Again some of the YouTube community proclaiming great welds on the $300 china unity… do you know what a weld is bro? do you live in a multi family dwelling …i sure hope not. i digress.
V1 of fet switched, isolated, spot welder pcb. 2oz copper, diy designed and etched
Resistive Spot Welder 10

The CD welders hand held electrodes didnt help either.  Resistive Spot Welding is tricky hand held, a constant pressure is requredd, too much or too little is no good. 

Resistive Spot Welder 11




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