I was at a loss how to calculate bus bar capacity for interconnecting batteries. Here you go.

https://youtu.be/XudtqDiyG5U
Paracord idea.

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Another work day today for my new battery. Presently the house is running on my first prototype battery which is NOT as neat as this. First of all the bus bars that come with LiFePO4 batteries are typically 2mm thick and are not suitable for the full amp capacity of the battery. So I bought 3/4 x 1/4 x 6’ lengths of 110 copper alloy. You need a BMS and the BMS needs to have a wire attached to each cell of a battery to keep a watchful eye on them. In my first prototype, I used crimp on ring lugs and didn’t route the wires neatly at all... I just wanted to see the thing work. In this battery I have made massive bus bars and even soldered the BMS sense wires to the middle of each bus bar. No need to stack ring lugs on the battery posts.

So I drilled them on my milling machine to get a really good consistent spacing on the holes. Never mind the few that are crooked... the vice came loose on the table. :-) I also drilled a shallow dimple in the middle of each bus bar to give a place for soldering the BMS sense wires on.

I placed a terminal strip up top in the BMS space on top of my battery. Each of the 17 sense wires comes to that terminal strip. This should make it really easy in the future to swap out a BMS or add an active balancer. I also ran an extra terminal on each end for 0v and 48v so I can attach 48v things without having do disconnect the BMS.

Note the shelf that the BMS will sit on has all thread down both sides that clamp the batteries in place. Also note that I build the battery from the bottom up and attached each bus bar as I went. This is to allow each battery to jockey around as I tighten the bus bars. You see they aren’t exactly true...they have a little warp in them (they are extruded). So if I had stacked all 16 batteries and then tried to tighten the bus bars, they might not have pulled the bottom batteries enough to make excellent contact on the terminals. So after all the bus bars were snug, I then used a nut on the shelf and all thread to clamp the batteries into the case so they won’t slide around. I have a little headspace at the top of the box above that shelf for hte BMS and contactor. Also there is a front cover and a top cover so I can keep it safely covered up.

Tomorrow I’ll hook up one of the two BMS units I have for testing and see it it is better than the chargery that I’m using on the prototype. Eventually, I’ll rework the prototype with bus bars like this one and I’ll have three identical units... 45kwh of LFP batteries.

Any of you building batteries for your house, cabin or camper may find this useful.

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