Make your own Battery pack – spot welding fun (part III)

Couple weeks ago we’ve ended up last time with having a battery rack ready. Honestly not everything went that good as I was hoping for since, so we’ve hit about a week-ish delay on my plan. It looks like spot-welding is pretty difficult without a proper spot welder! Luckily Richard came back with an idea that he has some DIY one which should do the job. Here it is!

As you can see, it is just a simple-huge capacitor with a resistor to shield it from crashing a power source. Risa invited me to demonstrate how it is working and while it was giving super-cool sparks results didn’t make me confident that this is a way to go.

As you see on the last picture – nickel was quite damaged and it didn’t look reliable at all. Anyway we had couple beers and quite a fun trying and I took a video of Risa doing his best – Thank you Riso! 🙂

Needed to move on with the project, I started asking all around if someone would be able to borrow me a spot welder for a day or two – and Chris Drake came back! Luckily he had a trip around practically a next day when having some errands in Brisbane and brought me his own. And here it is – including a bag of Nickel. Thank you Chris!!!

While it looks quite wild and carries practically no label, it feels very very solid. I tried to locate that product on a web to get one on my own and while I can’t be 100% sure I think it is this one. Santa, if you are reading this – this is what I need! 😀

Anyway, it came with instructions – have a Nickel 0.2mm thick, then wait for it to charge first and use it with settings: pulse 1 is 25ms, pulse 2 is 20ms. This seem to be important enough that the owner made a note for himself straight on the case:

Now having access to the spot welder we should have everything for getting it all done! Well, making your own battery is easy, but there are few bits where it things ca go wrong. Perhaps that most important one (Thank you Riso) is to make sure that all cells are balanced on a same voltage, mainly those in parallel connection as they will attempt to re-balance at the moment when they are connected – potentially leading to an instant and spectacular charge/discharge. No need to say that consequences can be … well let’s just do everything to prevent it.

As you can see on the picture below, testing was fun. Majority of all batteries was around 3.6V +- 0.05, which I think is ok.

How ever there were few which needed an additional push. Luckily it wasn’t much a problem with topping them up with our PSU.

Unfortunately couple of those also needed to discharge and as our PSU doesn’t have that feature, Sebi put together a device to take care of that. Man it took so long to discharge one from 4.4V back to 3.6 – almost a day! Sebi needed to add one of our spare hi-LEDs to get us moving.

Meanwhile we’ve progressed on some serious welding. I you are having an impression that pictures are not a in correct timing sequence – all good, we’ve been working on two batteries in parallel and I thought it wouldn’t look too good interlacing story between those two processes.

Anyway, when I’ve got things in my hands, I asked Oli and Sebi to have a go as well.

Boys were sort of enjoying it, and while Oli pretended that it is not his most favourite, he actually also did very good job! I also did a couple of videos, so there is an evidence that even kids can do this work.

Oli is spot welding like an old pro 😉
Sebi is spot welding like enjoying his dinner 😉

Well, let’s wrap it up here as there were many more things happening, but I don’t want posts to be too long. Anyway, well done guys and to be continued …

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