DIY Pulse Arc welding copper directly to cells

[bananu7]

A happy-ish medium could be to cover the deposit of the custom stepper while also getting access to a copy of the CAD files for the weld head as someone can always send them to PCBway or SendCutSend and get a one off part made if they need to. Just and idea

I second that. Local manufacturing almost always ends up cheaper for everyone involved and saves shipping and complicated logistics. The less custom parts the better - but if the stepper is necessary, so be it. I'd like to be on the list as well.

Out of curiosity, OP, do you think this it could weld ~0.2mm steel (I think?) electrodes on pouch cells together? That would make my battery build quite a lot simpler I'm thinking...

 

[devmonkey]

Yeh unfortunately nothing in this project is available off the shelf otherwise I would have used off the shelf parts obvs, everything is custom. You simply can't buy actuators with the required speed and accuracy so you have to build them, similarly you can't buy the current former you have to make it.

It can weld steel but it depends what you want to weld it to. What you struggle with is welding two materials with vastly different melting temps as you will vaporise one before it fuses with the other.

The stepper motor is a high quality unit designed to operate a feeder in a PNP machine, I have had it customised by the motor manufacturer to work in my weld head, I don't use it as a stepper at all rather as part of a highly precise very high speed closed loop actuator that I have developed specifically for this project. The motor is a good form factor for placing on the weld head and it isn't hugely expensive. The other CNC parts are just some small moving brass parts, electrode holder and the nozzle that acts as an argon chamber during the arc. All the other components are 3d printed in ASA (PLA also seems to work which is remarkable given the arc energy burst). 3d printing works for these parts as they contain internal gas channels that wouldn't be possible to fabricate on a mill.

Once I get the next set of boards in my hands for final validation I will work out costs for a kit. Will probably be $300-$500 depending on options and i'll put up a signup list.

My plan at the moment is the software running on the hardware with the very hard won algos i've developed both for electrode and arc control will remain closed source. However there will be an open api if people want to build their own tools to communicate with it over uart or usb.

 

[mrmojorising]

I'm not sure if this has been asked before, but out of interest how does this compare to those "pulse arc jewelry welders" you can get on Ali or Amazon e.g. https://a.aliexpress.com/_mOW1H6T

I know of at least one person that uses these for thin sheet metal, but has also successfully welded some cells with. Obviously not built for purpose, but would be interesting to know how it compares both performance and cost wise as I have very little knowledge of how these welders work

 

[devmonkey]

I don't think they work very well for battery welding, there are some people in this thread who have tried to use them who maybe able to comment, someone posted some pics of their attempts.

 

[Capekayak90]

I'm not sure if this has been asked before, but out of interest how does this compare to those "pulse arc jewelry welders" you can get on Ali or Amazon e.g. https://a.aliexpress.com/_mOW1H6T

I know of at least one person that uses these for thin sheet metal, but has also successfully welded some cells with. Obviously not built for purpose, but would be interesting to know how it compares both performance and cost wise as I have very little knowledge of how these welders work

From my understanding the biggest problem with these kind of welders for battery welding is two fold. One is repeatable fixturing of the welder stinger to the battery pack as the distance and position remaining the same every time is critical. The second and arguably harder issue to get around is dialing in a good weld.

Full disclosure this is some armchair engineering and not first hand experience but considering this is the internet its clearly my duty to push my ignorant opinions on others. Anywhoos...These cheaper no name pulse welders likely have issues with a precise and linear resolution on the lower end of power which is likely where they would be used for welding batteries. In example level 5 on power is too low but level 6 on power is too high. They also likely don't have the repeatability that name brand arc welders have, especially at those low levels. I don't mean this in terms of quality control but rather in terms of how the welder controls and meters its output. As the welder operates it's temperature will rise and its internal resistances will increase (generally speaking) which will affect its output.

All of that being said, I'd be willing to bet that if you spent enough time with it, warmed it up on some test pieces before hand and make a jig to fixture the batteries in place, and maybe messed around with the shape of the tungsten on the electrode, you could probably make it work. I wouldn't be surprised if you could even reverse engineer it and modify its control system to work better with batteries. Just my 2 cents

 

[devmonkey]

Off the top of my head these are some reasons they are unsuitable, these were discussed earlier in this thread if you go back a bit.

They don't control energy delivery, they just discharge a capacitor, total energy set by charge voltage only, they try to control current by switching in banks of power resistors. This effectively means you are running full current during retraction which will blast copper all over the electrode meaning it isn't repeatable.

They do not control the retraction position at all they just fire a solenoid meaning your fixturing needs to account for electrode wear and you can't control electrode pressure which means you can't press the copper onto the cell end at the point the weld pool with develop meaning it won't stick very well.

So overall they don't control the current waveform during retraction since they don't know where the electrode is which is critical for battery welding copper. Without control of the waveform wrt electrode position and pressure you don't have control of the weld puddle so anything can and will happen.

I believe most jewelry welding uses low double digit energy levels, I have found 70-90J of true energy into the arc after accounting for all losses is required for perfect welding of 0.3mm copper to cells.

If you look at the commercial pulse arc battery welders they are completely different from the commercial pulse arc jewelry welders sold by the same companies, I think the cheap Chinese units and the commercial jewelry welders are likely similar for freehand jewelry welding but neither are any use for battery welding.

That being if you have one I'd like to see it tried. My first attempts used a solenoid and a switched resistance current former, they weren't great.

 

[troubled81]

Any idea on when you will be offering this to buy or releasing the design? I have a got the cells and finished designing and printing my test pack. The only thing I need now is the welder. I am excited to see if my little liquid cooled 6P4S pack can dump the current I need it to and test the voltage sage under load.