A quick lesson for you about batteries and BMS (battery management system). LFP or LiFePO4 48v batteries are made of 16 individual cells arranged in series. Although we say its a 48v battery, it actually reads 55.2v when full and 46v when empty. Kinda like how 2x4's aren't really 2x4 inches.

1)The BMS keeps tabs on the 16 individual cells. If one is too high or too low voltage, the BMS will shut down that battery so that one cell isn't damaged.
2)The BMS will level the charge between these cells. Let's say your battery is at 55.2v, a perfect 3.45v per cell right? Maybe not... maybe 15 cells are at 3.44v and one cell is at 3.6v. The BMS will take voltage from that one high cell and distribute it to the others. This is called top balancing.
3)The BMS will use it's canbus interface to communicate the SoC (State of Charge) to the inverter. It will also advise the inverter not to charge the battery if it's too cold or the battery is full.

Point 3 is what I want to expand on. If you have more than one battery and BMS, you could connect them all to the inverter on canbus. The problem is the inverter would hear each BMS squawking it's SOC and the inverter wouldn't know who to listen to. The display on the inverter would change rapidly as each battery told the inverter a different SoC. Can you imagine 4 people in a room shouting 100% 95% 98% 99%? How confusing it would be.

The solution to this is that you nominate one battery to be the spokesperson. Only that battery speaks to the inverter. Behind the scenes the batteries talk among each other using RS485. The spokesperson collects data from each of your batteries, consolidates it into one number and tells the inverter.

So now you know why server rack batteries have RS485 and CANBUS ports!

The JK BMS is smart enough to take into account that you might have mix-matched different capacity batteries. When these batteries communicate over RS485 they tell the master bms what their stated capacity is and how many amphours they have left. So you can absolutely mix 5kwh, 16kwh and 32kwh batteries together and it'll work just fine.

Another "back to basics" lesson today... If you have a group of batteries and decide to add an additional battery, how exactly do you do that? Even a small voltage difference can result in extremely high amps between batteries.

For example, you have a new battery sitting at 53.0v and the other 6 batteries are at 53.8v.... if you connect them together there will be several hundred amps between batteries for a few minutes. It will likely trip a circuit breaker or blow a fuse.

So you have a few options:
1)set the battery with the lower voltage to not allow charging. You can do this from a bluetooth app in JK BMS and many other brands. Connect the battery and nothing happens. After sundown your other 6 batteries will get drawn down. As their voltage drops below the voltage of the new battery, it will begin to discharge with the rest. First thing in the morning, check to make sure that all batteries are at the same voltage and use your bluetooth app to re-enable charging. Now all of them will charge at once.

2)The other method is if you have the server rack version of JKBMS with a big wire toroid coil in the top right corner, you can simply connect the batteries together if the new one is a lower voltage than the rest. What will happen is that a lot of amps will flow into the new battery for about 3 seconds. The BMS will disable charging and go into low amp charging mode (limp mode). It will charge at 10 amps until it's voltage matches the other batteries in your "herd". At that time it will automagically revert to normal operation.

JK BMS with charge current limiter. upper right corner

Don't have a source on this one, but some good ideas here. 🏕

imagine drunkdriving the sneedclanker on city property 🤩

I finally found a place where I can write my manifesto.

Good stuff on meshcore tonight. Keep in mind I’m in South Carolina. This message is from Tennessee.

I just watched the jankiest electric lawn mower conversion I've ever seen... and now I'm thinking of taking an old lawn tractor and converting it to move the pig pen around the back pasture.

You install a 120v ordinary electric motor and use it to drive the hydrostat drive... you install a 3kw inverter and a battery. done.

https://www.youtube.com/watch?v=XNEHsN625M0

I wanted this pole barn to face south broadside. So I looked online for when the sun would be dead east. That time changes from day to day. So I marked it using the shadow of an existing post.

We laid out the building and fast forward to today and solar noon was 13:26. I took this picture at 13:27. As you can seee the trusses make a straight shadow to the posts on the north wall. I got it right!