Busbar Question for 4x 12v Batteries in Parallel

[Dagoth Ur Does Solar]

I currently have a single 12V 230Ah LiFePO4 battery in my system, with a BMS rated for 200A of continuous current. I have been considering, in the future, adding additional capacity, of at least 1 more, but up to 3 more of the same battery, so that I can have a couple of days of powering light critical loads (i.e. chest freezer).

I have been thinking about the best way to wire this up, as well as fusing my batteries. My understanding is each positive lead to the battery would ideally have a fuse (in case the overcurrent protection of the BMS fails).

Here's my ignorant question: When paralleling 4 batteries, how do you determine the amperage rating of the busbar used for connecting all the batteries? I assume this would not need to be the compared amperage, right? If I had a 400A max continuous discharge load from inverters/other devices, I would want to rate the busbar for 400A + a safety margin, correct? It wouldn't need to be 800A (summing the BMS' amp rating), right? Could I just grab a 500A quality busbar and call it a day?

Question two: It looks like most busbars for higher amperages tend to only have 4 terminal posts. If I had four batteries, ideally, I would need at least a 5 post busbar to account for my positive and negative leads heading off to the rest of the system, right?

 

[chrisski]

When paralleling 4 batteries, how do you determine the amperage rating of the busbar used for connecting all the batteries? I assume this would not need to be the compared amperage, right? If I had a 400A max continuous discharge load from inverters/other devices, I would want to rate the busbar for 400A + a safety margin, correct? It wouldn't need to be 800A (summing the BMS' amp rating), right? Could I just grab a 500A quality busbar and call it a day?

If your max pull from the inverter, including DC losses, and also including any DC loads in your system is 400 amps, then yes, a 500 amp busbar is sufficient.

IMO, if you're pulling 400 amps, you need to step up to a 24 volt or even better 48 volt system.

Question two: It looks like most busbars for higher amperages tend to only have 4 terminal posts. If I had four batteries, ideally, I would need at least a 5 post busbar to account for my positive and negative leads heading off to the rest of the system, right?

I say yes you need five studs, and perhaps more for growth. The additional studs could be to feed in an SCC or wire a battery charger. I have a 1000 amp 8 stud busbar, and all 8 studs are filled.

I have seen bigger busbars that are rated to have multiple terminals on a stud, but I don't see how I would physically fit two of those bigger wires and thicker lugs flat on a busbar, never mind the four terminals the spec sheet said a stud could handle.

 

[Dagoth Ur Does Solar]

If your max pull from the inverter, including DC losses, and also including any DC loads in your system is 400 amps, then yes, a 500 amp busbar is sufficient.

IMO, if you're pulling 400 amps, you need to step up to a 24 volt or even better 48 volt system.

Right- that's what I thought. And yes, I currently only have a 1000W AIO inverter on the battery (so something in the realm of 83A continuous draw at a maximum), but I was just creating a hypothetical.

I say yes you need five studs, and perhaps more for growth. The additional studs could be to feed in an SCC or wire a battery charger. I have a 1000 amp 8 stud busbar, and all 8 studs are filled.

On the positive side, my intent is to wire up my Victron shunt in between the battery paralleling bus bar and a second bus bar where all my loads will sit. Logically, this seems to be what I would need to do, unless I am missing something here. Am I thinking about that the wrong way?

 

[chrisski]

On the positive side, my intent is to wire up my Victron shunt in between the battery paralleling bus bar and a second bus bar where all my loads will sit. Logically, this seems to be what I would need to do, unless I am missing something here. Am I thinking about that the wrong way?

Yes having a second busbar for loads is a better way to do what you want instead of putting everything on one busbar.

The Shunt seems located in the correct place. Mine is on the negative side as per setup instructions. I'm sure yours is also.

 

[Dagoth Ur Does Solar]

Yes having a second busbar for loads is a better way to do what you want instead of putting everything on one busbar.

The Shunt seems located in the correct place. Mine is on the negative side as per setup instructions. I'm sure yours is also.

I'm sorry, just a mixup. I meant negative. I had the thought of doing the same on the positive side with a fuse, although as I was thinking about plans, I figured each battery should have its own terminal fuse.

Although, my battery is a 5/16" stud, and finding a good terminal fuse for a 5/16" stud seems difficult. The "good name brands" like Blue Sea use 3/8ths. Not sure if I could get away with putting a 3/8ths terminal fuse on my 5/16" stud.

 

[chrisski]

Although, my battery is a 5/16" stud, and finding a good terminal fuse for a 5/16" stud seems difficult. The "good name brands" like Blue Sea use 3/8ths. Not sure if I could get away with putting a 3/8ths terminal fuse on my 5/16" stud.

I got the SELTERN marine grade lugs from Amazon. The copper was thick and also tinned. Also available in 5/16"

I avoid putting the 3/8ths terminal on a 5/16th stud. If it came to the last lug of the build, I'd use it with the intention of installing a the proper lug later. Not sure what everyone else does.