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index  plan banking
Plan - Assigning banks
Dividing battery packs into banks.
The Elithion Lithiumate™ BMS can handle battery packs with up to 255 cells in series.
For technical reasons, and for increased reliability, the BMS views the battery pack as composed of a number of groups, called "banks".
(This does not mean that the pack itself is physically divided in sections: this is only with regards to the way the BMS sees the pack.)
A Bank is a set of cells wired in series that communicates with the controller through its own communication cable.
So, if the pack is divided into 3 banks, there are 3 cables between the BMS controller and each one of those banks.
This page will guide you in the process of dividing the pack into multiple banks.
While it is convenient to divide a pack into banks of equal number of cells in series, that is not necessary, and indeed is not always possible
For example, a pack with 48 cells in series may be easily divided into 4 banks of 12 cells each.
However, if the pack is physically divided into 2 sections, one with 29 cells in series and the other with 19 cells in series, then it could be divided in banks of 14, 15, 9 and 10 cells respectively.
When choosing the number of cells per bank, two opposing criteria must be considered:
- On one hand, for reliability, it is best to use many banks: should 1 bank fail to communicate, the other banks can be used to guess the state of the one bank
- On the other hand, for convenience, it is best to use few banks: fewer banks require fewer cables, and the assembly time and the cost are lower
The rule of thumb is that a bank should have between 8 and 16 cells in series.
As far as the BMS is concerned, each pack is divided into a number of banks:
- There is at least 1 bank, but more than 1 is recommended
- There can be up to 16 banks
- Banks are numbered starting from #0 and up to #15:
- The bank number is not programmed in a cell board: all cell boards are completely identical
- The number of a bank is set by where it is connected on the BMS controller
- Bank #0 is the bank connected to connector #0 on the BMS controller, and so forth
- Swapping two banks' connectors on the BMS controller will swap their number
- Banks must be contiguous, starting from #0:
- On the BMS controller, one of the banks must be connected to the connector Bank #0
- The other banks must be connected to the following connectors, in order: #1, #2, etc.
- There cannot be empty bank connectors between sets of filled connectors: e.g.: #0, #1 and #3 is NOT OK
- If groups of cells are physically separated, a bank cannot be across that physical separation: use separate banks in each group of cells
- More banks improve the reliability in case a cell board stops communicating or a cable breaks
- Fewer banks improve the reliability and the layout by reducing the number of cables
- Fewer banks reduce the material costs and the installation labor
- In the end, the number of banks is usually set by the rule of thumb on the number of cells per bank, below
Each bank handles a number of cells in series:
- Cells are numbered from #0 and up, up to #255
- The cell number is not programmed in a cell board: all cell boards are completely identical
- The number of a cell is set by where its bank is connected on the BMS controller and by the position of the cell within that bank
- Cell #0 is the most positive cell in the bank connected to connector #0 on the BMS controller
- Cell #1 is the second most positive cell in the bank connected to connector #0 on the BMS controller
- Etc.
- Each bank can be set-up to handle as little as 1 cell in series;
however, if using standard cell boards, 2 cell is the minimum: a positive end and a negative end cell board;
if a 1-cell bank is required, please contact Elithion for a quote for a design of a custom cell board
- Each bank can be set-up to handle up to 63 cells in series;
however, for technical reasons, it is recommended that a bank have no more than 16 cells, 20 at the most
- The rule of thumb is that a bank should have between 8 and 16 cells in series
- While different banks may have different number of cells, it is convenient to have all the banks at similar or even equal number of cells in series:
- If using a cell board designed for multiple cells, the same shape cell boards can be used throughout the pack
- The time it takes to communicate to all the cell boards is proportional to the number of cells in the bank with the most cells in series; therefore, spreading the cells evenly results in faster communications
- Cell's position within a battery:
- Technically, there is no need to correlate a cell's electrical position within a battery and its position within the banks. However:
- To aid layout and troubleshooting, it is best if cell #0 and bank #0 are assigned to the most positive cell in the battery pack. Then:
- Cell #N will be the Nth most positive cell in the entire string of cells in series
This table shows an example of a battery pack with 17 cells in series.
| Bank #
| Number of cells
in series
in each bank
| Range
of cell numbers
of the cells
in each bank
(most positive
to most negative)
|
| 0
| 5
| #0 to #4
|
| 1
| 5
| #5 to #9
|
| 2
| 7
| #10 to #16
|
This table shows examples of how many banks may be used, and how many cells might be used per bank.
| Bank #
| Number of cells in series
|
| 10
| 20
| 30
| 40
| 50
| 75
| 100
| 150
| 200
| 250
|
| 0
| 5
| 7
| 10
| 8
| 15
| 15
| 10
| 15
| 15
| 16
|
| 1
| 5
| 6
| 10
| 8
| 14
| 15
| 10
| 15
| 14
| 16
|
| 2
| -
| 7
| 10
| 8
| 11
| 15
| 10
| 15
| 14
| 16
|
| 3
| -
| -
| -
| 8
| 10
| 15
| 10
| 15
| 14
| 15
|
| 4
| -
| -
| -
| 8
| -
| 15
| 10
| 15
| 15
| 16
|
| 5
| -
| -
| -
| -
| -
| -
| 10
| 15
| 14
| 15
|
| 6
| -
| -
| -
| -
| -
| -
| 10
| 15
| 14
| 16
|
| 7
| -
| -
| -
| -
| -
| -
| 10
| 15
| 14
| 15
|
| 8
| -
| -
| -
| -
| -
| -
| 10
| 15
| 15
| 16
|
| 9
| -
| -
| -
| -
| -
| -
| 10
| 15
| 14
| 16
|
| 10
| -
| -
| -
| -
| -
| -
| -
| -
| 14
| 16
|
| 11
| -
| -
| -
| -
| -
| -
| -
| -
| 14
| 15
|
| 12
| -
| -
| -
| -
| -
| -
| -
| -
| 15
| 16
|
| 13
| -
| -
| -
| -
| -
| -
| -
| -
| 14
| 15
|
| 14
| -
| -
| -
| -
| -
| -
| -
| -
| -
| 16
|
| 15
| -
| -
| -
| -
| -
| -
| -
| -
| -
| 15
|
In some cases, a battery pack consists of multiple strings in parallel.
The Lithiumate™ BMS can handle such battery packs.
Note that, when using strings in parallel, the BMS cannot estimate cell resistance, because the pack current divides unequally among the strings in parallel.
- There can be up to 9 strings in parallel for version 1.XX of the software and up to 16 strings in parallel for version 2.XX of the software.
- Batteries are numbered from #0 and up, up to #8
- A bank cannot belong to different strings: use separate banks for separate strings in parallel
- The way one battery is divided into banks can be different from the way other strings are divided. For example:
- String #0: 3 banks: 6 cells, 6 cells, and 6 cells (total = 18 cells in series)
- String #1: 3 banks: 4 cells, 6 cells, and 7 cells (total = 18 cells in series)
- String #2: 4 banks: 4 cells, 4 cells, 4 cells, and 6 cells (total = 18 cells in series)
- However, for obvious reasons, the total number of cells in one battery in parallel has to be the same as the total for each of the other strings in parallel
- The maximum number of banks in series that the BMS can handle is less than it would be for battery packs with a single series string, because the total of 16 banks is divided equally among strings in parallel:
- 8 banks each if using 2 strings in parallel
- String #0 uses Banks #0 and up, sequentially
- String #1 uses Banks #8 and up, sequentially
- 5 banks each if using 3 strings in parallel
- String #0 uses Banks #0 and up, sequentially
- String #1 uses Banks #5 and up, sequentially
- String #2 uses Banks #10 and up, sequentially
- 4 banks each if using 4 strings in parallel
- String #0 uses Banks #0 and up, sequentially
- String #1 uses Banks #4 and up, sequentially
- String #2 uses Banks #8 and up, sequentially
- String #3 uses Banks #12 and up, sequentially
- 3 banks each if using 5 strings in parallel
- String #0 uses Banks #0 and up, sequentially
- String #1 uses Banks #3 and up, sequentially
- String #2 uses Banks #6 and up, sequentially
- String #3 uses Banks #9 and up, sequentially
- String #4 uses Banks #12 and up, sequentially
- 2 banks each if using 6 to 8 strings in parallel
- String #0 uses Banks #0 and may use bank #1
- String #1 uses Banks #2 and may use bank #3
- String #2 uses Banks #4 and may use bank #5
- String #3 uses Banks #8 and may use bank #7
- String #4 uses Banks #8 and may use bank #9
- String #5 uses Banks #10 and may use bank #11
- (String #6 uses Banks #12 and may use bank #13)
- (String #7 uses Banks #14 and may use bank #15)
- 1 bank each if using between 9 and 16 strings in parallel
- String #0 uses Banks #0
- String #1 uses Banks #1
- etc.
This table shows examples for a pack with 16 cells in series: how many banks may be used, and how many cells might be used per bank.
| Bank #
| Number of strings in parallel
| String #
|
| 1
| 2
| 3
| 4
| 5
| 6
| 7
| 8
|
| 0
| 16
| 16
| 16
| 16
| 16
| 16
| 16
| 16
| 0
|
| 1
| -
| -
| -
| -
| -
| -
| -
| -
|
| 2
| -
| -
| -
| -
| -
| 16
| 16
| 7
| 1
|
| 3
| -
| -
| -
| -
| 16
| -
| -
| 9
|
| 4
| -
| -
| -
| 8
| -
| 16
| 16
| 6
| 2
|
| 5
| -
| -
| 16
| 8
| -
| -
| -
| 10
|
| 6
| -
| -
| -
| -
| 16
| 16
| 16
| 5
| 3
|
| 7
| -
| -
| -
| -
| -
| -
| -
| 11
|
| 8
| -
| 4
| -
| 16
| -
| 16
| 16
| 4
| 4
|
| 9
| -
| 4
| -
| -
| 16
| -
| -
| 12
|
| 10
| -
| 4
| 16
| -
| -
| 16
| 16
| 16
| 5
|
| 11
| -
| 4
| -
| -
| -
| -
| -
| -
|
| 12
| -
| -
| -
| 9
| 16
|
| 16
| 14
| 6
|
| 13
| -
| -
| -
| 7
| -
|
| -
| 2
|
| 14
| -
| -
| -
| -
| -
|
|
| 13
| 7
|
| 15
| -
| -
|
| -
|
|
|
| 3
|
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