I have 4 sets of 2 batteries (12v 100ah) that are from different brands but same specs. i want to add a battery balancer to ensure they stay balanced and i see i need to have a positive negative and midpoint bus bars. I understand the + and - bus bars and that i need to connect each of the - to the - bus bar and the + to the + bus bar but the midpoint one confuses me. so i currently have a 3" 4awg jumper with ring terminals on each end connecting each of the + to the - of the sets to have them in series.
when i set up a midpoint busbar, do i leave the current setup the way it is and just run another lead from one of the midpoint terminals (- or +) to the midpoint bus bar? that way the jumper connects them in series then that is connected to the midpoint busbar or is there another way? im not too sure. i tried looking it up and from what i understand it says to take those jumpers off and connect them to the mid point busbar.
however, this doesnt make sense to me. if i take the jumper wire off from the - and + and connect it to the busbar how is it connected to the battery midpoint then and arent the batteries now not in series? whats the right way to do it? like how exactly do i connect the midpoint (- and + that connect the 2 in series) to the bus bar properly?
no bc they actually show this which makes more sense but that seems to make the leads really long and it says to make them the same size so im trying to figure out where the best place for it to go would be for all the connections to be proper:
Basically theres no examples of anything like this anywhere for real world examples. thats what i was wondering how do ppl normally do this? i was thinking i want the batteries as close to each other as possible while still allowing room for heat dissipation and the jumper between the + of battery 1 and - of battery 2 is 3" so theres like an inch between the batteries. i guess i could build some sort of thing to put over the batteries or close to them and attach the mid point bus bar to that and it would sit above the batteries but in the middle and that way the sense wires and the midpoint wire from the balancer are able to reach while staying under 30cm.
the issue is I have to come up with everything from scratch and i feel like inevitably ill be making mistakes that i could avoid by learning from those before me but i dont see where those examples are
I thought you were asking after the principle rather than asking for actual examples, apologies.
The third image which I edited shows mid point cables, which will be heavy gauge to carry the full bank current. Using a bus bar will mean longer cable and more connections so more resistance and need more space to mount it all, the only benefit may be slightly better balancing. This is probably why there are no examples, people do not do it, they just add some 70mm2 or so mid point cables as it is simpler, cheaper, more compact, less resistance.
I have never liked that image from Victron. They say the balance cable needs to be full current rating, but they draw it thin. Optima do a good write-up up I have the link. Additionally, you should fuse the connection between each battery for better protection. If one fail, the good battery will start dumping its current into the bad one.
Thank you very much for your advice. I never considered putting a fuse between the batteries. I only paid $100 per 12v 100ah LiFePO4 battery so I don’t exactly have all the confidence in the world in each one. That’s actually how I ended up with 8 batteries from 4 different brands. I would buy 2 and plan to test them and if they were good I was gonna buy more but the sale would go away right away.
Regardless, I definitely am going to look into putting a fuse between the sets of batteries bc I don’t think I can put a fuse between 2 batteries in series. I’m not even sure how that would be done since I only ever heard of putting the fuse on just the main positive coming from the entire battery bank. i will check out the link you posted. Thanks again.
I use an MRBF fuse between parallel banks. This is very compact. The parallel/balance cables need to be full current capacity, so you would expect to protect it against overcurrent.
