jiggyjonboat said:
question is do I do wire batteries up with 4 banks of parallel cells then wire for the 4s after? Or wire the batteries into series first then branch off for the 4 banks of parallel groups. ?
If you wire 4p then 4s, which is a 4s4p configuration, then you'd only need 1 bms, as OffGridInTheCity mentions. If you wire it up as 4s then 4p, which is a 4p4s configuration (I know, can be confusing on the naming conventions), then you'd need 4 bms units, 1 for each string of series.
I personally would recommend 1 bms, or 4s4p. Reason being, is if you have multiple bms sharing a common output, it's possible 1 of them could shut down prematurely, which would cause a shift in current flow from the other strings and over load those as well. Depending on the current draw, this "could" burn out the FETs on the bms, requiring replacement.
This is, of course, if you are using a cheapo bms from chinesium manufacturing. If you are using something quite a bit more robust and smarter, then that makes it more of a funds available question than anything else.
In both situations, 4s4p or 4p4s, they are electrically identical on the absolute outputs. Charging/Discharging would be more or less the same. The only issue that "could" come up with 4p4s, is that one of the cells in one of the strings could become a different voltage than one of the other cells in another string. This would cause a little imbalance in the system. This would be the "primary" reason to have a smart bms that talks to the others, or go with 4s4p and use 1 bms from the get go.