This is a direct continuation of my previous article Make your own Battery pack – spot welding fun, so if you haven’t read it, get there first or you’ll be missing lots of context.
We’ve left of when most of welding was already done and while we instantly jumped on a battery wrapping an wiring I still needed to do a bit of review of all material we’ve been able to collect to progress further.
On the picture above you see two main (to be) battery packs in their racks. That makes two-times 6×5 battery cells + 4 spare ones. There are three packs of 2C Nickel strips, two 6S balancing cables and two male XT90 connectors. There is also a box with two 6S 30A DALY BMSs (Battery Management System), which came from China through Fedex and just getting them to my hands would be a story on its own.
BMS above is a clearly a hero of our today’s story. Our current situation is that we have one completely welded battery pack, but it still needs proper wrapping and needs to be connected to the BMS. Let’s start with wrapping. One layer of Kapton did a job to make it more look compact.
Wiring next. Wiring instructions are bit cryptic, but pictures are sort of self explaining.
So it is simple .. just connect all cells in parallel sets to its relevant cable and don’t mess up! How about this? Actually I’ve learned a lot – mostly that when it is all coming to life you are starting to deal with some interesting currents here. There were couple times more sparks than what I would like and also got buzzed once from that welder.
I have just a little idea what I am measuring here, but Vlada says it is a working-resistance. It needs to be between 0 and 5Ω and it says 0.2. I think we are fine. I used a bit of Velcro to strap that BMS to the battery.
Last bit was more Kapton wrapping. Looks beautiful, doesn’t it?
Being super happy, I also took a video to show off with our master-piece. 😉
Next stage – darn how could you exactly charge this thing? Luckily once you have some reasonable BMS there, things are getting pretty easy – just connect it to some reliable PSU and BMS will take care of rest.
It took couple hours, so Sebi setup a tiny monitoring set.
And here is our IT guru monitoring the charging itself from the comfort of our kitchen.
I don’t have a picture showing how that battery pack looks all charged, but our multi-meter was reporting some 25.2V. Still took a last shot, putting our final product on scales to check how we are doing weight-wise – reading pretty much 2.5kg on the dot.
This was one seriously productive weekend, can’t wait to see how it performs!