Charging LiFePo4 in a hybrid system

@JJH3rd
I have a setup similar to yours, although my LFP bank is one fourth the size, and I definitely agree with mcgivor. A 51V to 51.4V absorb setting would be the highest safe settings for your bank without a BMS. With that charge setting it should work well if you have already balanced the cells.

Here are two BMS that do cell voltage monitoring with cell and battery protection capability. They do not do active cell balancing. One is a Beaglebone/Raspberry Pie project, information here:

https://github.com/simat/BatteryMonitor

and the other is the Chargery BMS16 (works with 2 to 16 cells in series or series / parallel configurations) available here:

https://www.aliexpress.com/item/32850502583.html

JJH3rd said:

Here's my basic quandary.  When I examine the BMS landscape, I see that they work with the battery bank as a whole.  This approach may be alright when there are a small number of batteries, less than 10 for example.  The number of small voltage LFP batteries needed to get to a workable voltage exceeds that number by a large margin.  In my case, to get to ~48 V & 800 AH, I have 30 batteries (15s2p). I would like to believe that a BMS I would install would provide more features than the Sol Ark controller to which the batteries are attached.

At this point, I would settle for information on each cell, such as voltage and SOC for instance.

I may have to construct an Arduino based monitoring system.

There appears to be a little confusion on your behalf, a BMS looks not only at the total voltage but also individual cell, or cell block voltages. Your battery consists if 15 cell blocks in series, a cell block being 2 cells in parallel, each 400Ah CALB  unit is not a battery, it is a cell.

Attached is a pdf of the BMS I currently use, it is an 8 series but illustrates how it is connected, in your application the only difference would be the addition of 7 cells to meet the required voltage. They are available in many configurations depending on personal needs such as charge/discharge current and voltage. For around  $100 I considered it cheap insurance considering the overall cost of the cells.

As mcivor said, a 15S BMS is called for because the parallel block doubles the amp hour capacity while the voltage remains the same. I'd also recommend increasing the BMS current capacity to better handle surges. Take a look at this one.

https://www.aliexpress.com/item/32997552090.html?spm=2114.12010612.8148356.2.42c43de2I8pAHH

Whilst there is nothing wrong with the configuration using 2 strings of 15 cells each with its own BMS there are some considerations that need to be considered. The maximum current would need to be limited to the maximum each BMS can process, for example if 190 A is the maximum both would need to be capable of handling that value to prevent overloading of the BMS  should one disconnect for any reason as LiFePo4 will absorb extremely high current, usually 1C or greater.

The conventional method is to connect  two, or more cells in parallel first then series, this would mean only a single BMS would be required as the multiple cells in parallel  become one cell block. This is how small cells not much larger than an AA cell are configured, often with hundreds in parallel in automotive applications. With larger prysmatic cells it's common to parrallel 100Ah cells in parallel in order to increase capacity  rather than use large 400Ah as it's reputedly a better method. Naturally doing this will require only a single BMS, there may be some perceived logic of redundancy with a dual BMS as shown, but having all the cells as a common battery keeps things simple

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