Gave up and installed a BMS

Yes, it's true. I gave up and installed a BMS. A Battery Monitoring System, that is. Not the kind that drains a few of your cells and then their buddies destroy them at the earliest opportunity. No, the kind the measures two voltages. Whole pack voltage and half pack (more or less).

 The brains of my BMS.

In my case the half pack is the first 13 cells. What this gives me is four interesting figures:

• Average cell voltage (total voltage divided by number of cells)
• Average cell voltage for the first 13 cells (their total voltage divided by 13)
• Average cell voltage for the last 12 cells (total voltage minus first 13 cells divided by 12)
• Difference in average voltage between first 13 and last 12 cells.

That last bit of information is very interesting, because if it is more than say 0.2 volts, there must be a problem with one of the cells in either part of the pack. All data goes to my Zabbix server, which can alert me, if that happens. I also have Grafana set up, so I can some pretty graphs too.

Now you may ask how do I measure the first 13 cells and not cause an imbalance? Well done, my young Padawan, that is the right question. Well, I have a relay in the loop, which only connects the first 13 cells for a very short time, less than a second, currently every three minutes. The load imposed on the first 13 cells is also something like 0.1 watts. This should not cause a problem even in the long run. And if it does, I'll know about it.

I've used a LinkIt Smart 7688 Duo for a couple of IoT things now, so that's what I used here too. You can get easy to user Grove parts with sensors and the like from Seeed. They're really quite handy if you're as lazy as me and don't want to be soldering every last thing yourself.

Solar controller for charging the car.

I also now charge the car on solar. I have a couple of panels installed which actually charge my motorcycle first and from there I can charge the car, if it pleases me. But more on that later. The motorcycle has had a bit of a make-over as well. It's been about two years since the last post, so if you waited this long, perhaps you can wait a bit more for those as well. Anyway, good times.

ps. Don't pay attention to the grounding cable on the battery box. I've been meaning to hide it for six years now. It's going to happen any day now. Really. Maybe.