How it started…
A couple of years ago, I started to build my own gobox. With this gobox, I included a lead acid battery to power it. The battery became a paperweight within weeks (A small design error caused a small standby current. What again caused the battery to be drained). The first of a series of changes are made to the gobox. The latest change was, no battery power at all! Running directly from a power supply, which was fed by my generator. And this version did run for two years, without any power issues.
But taking a generator and fuel with you, you won’t be very portable. So my ideas then went out to a small but powerful battery. Still with the idea of using a lead-acid battery. The big disadvantage of this battery type is that once the power of the battery increases, the weight also increases. And to take a 20 kg battery with you, that’s not easy either.
I know lithium batteries for years now, but never considered these as a useful source for my gobox. After I saw a couple of youtubers, which were using lithium cells, to power their home. I was convinced that this can be my next powersource. So I was digging into this subject. And find out that these lithium cells, also know as 18650, could be packed as a multicell lithium battery.
After getting more and more information, I bought 10 lithium cells. To start gathering more knowledge and understanding of their performance. I start using these cells for all sort of projects.
I also discovered that shorting these cells, could damage them, but also increasing my heartrate 😉
The name 18650 means, 18 mm diameter and 650mm long.
Planning lithium battery
After a while, I start searching for building a large usable battery for my gobox. I found several websites and tutorials which gave enough information to build my own battery pack. So I start planning and design.
First I needed to determine for which capacity, this battery will be built. My first lead-acid battery for to Gobox was a 34Ah (2x 17Ah in parallel). So I knew it has to be in the region of that size.
I decided that it should be a 4S12P (4 cells in series and 12 in parallel). That brings me, (fully charged) 16.8V/41Ah and fully discharged 12V. I had changed my mind a couple of time, from 3s (which gives me fully charge 12.6v and discharged 9v. Effectively you can use only a small portion of this battery (12.6 till somewhere of 11.0v).
I made some scheme how I should wire this batterypack.
After all this planning, I finally started the build. First ordered my new 18650 cells. My first pack would be built from new cells, later packs would be built from reclaimed cells from old laptop batteries or cells from e-bikes.
When these cells arrived I charged and discharged them, to see what their capacity is. I bought 3300mAh cells. But most of them are 3400+mAh.
After that, I start the actual build. First, lay the holders in the pattern you want.
After that, I can start arranging the cell according to their capacity. So the packs are capacity-wise evenly balanced.
When every cell is placed, it’s time to start up the welder. Well…. It’s just a lead-acid battery with a controller.
After some 400+ welds, the batterypack was completed and also worked.
And as last point I installed the BMS (Battery Management System), which controlled the battery, and takes care of the balancing of the series.
And now it’s time to do some serious testing with it.
Soon more about this testing
Below you will find some photos of me building the battery: