1.1. Cell Voltage

Cell voltage limits are highly restricted by cell manufacturers on its datasheets. To have safe battery systems, cell voltage limits must be set correctly. These parameters can be configured by "Cell Settings" tab of LiMon PC Tool. Our battery management system boards, fits perfectly of any of lithium chemistry like NMC, LFP, LTO, NCA etc. Nevertheless, user need to reconfigure the parameters by using datasheet of exact model of lithium cell.

Warning

User has the responsibility of setting proper thresholds by our software. Otherwise, safe limits could be exceed and unstable dangerous situations can happen.

1.1.1. Cell Voltage Protection

Our battery management system boards always measure the individual cell voltages many times in a seconds. Cell voltages of a lithuim battery has little tolerances at the top or bottom voltages. To get safer and long life battery system, user need to avoid of either over or under cell voltage at any time. If any limits are exceeded over allowed period of time, BMS will take an action to protect battery pack.

Diagram.1.1.1: Cell Voltage Protection

flowchart TB

  classDef Event_Protection fill:red,color:white,font-weight:bold,stroke-width:0px
  classDef Event_Warning fill:yellow,color:black,font-weight:bold,stroke-width:0px

  a1[Measure and Check Cell Voltages] 

  a3(is Any Cell Below Under </br>Voltage Protection Limit?)
  a4(is Any Cell Higher Than </br>Over Voltage Protection Limit?)
  a5(is Any Cell Below Under </br>Voltage Warning Limit)
  a6(is Any Cell Higher Than </br>Over Voltage Warning Limit)

  w1([Cell Under Voltage Warning Occured])
  w2([Cell Over Voltage Warning Occured])

  t5(O.V.P. Delay Time Exceed?)
  t6(U.V.P. Delay Time Exceed?)

  r1([Do Protection Action])

  a1 --> a5 
  a1 --> a6
  a5 -- NO --> a1
  a6 -- NO --> a1
  a5 -- YES --> a3
  a6 -- YES --> a4
  a3 -- YES --> t6
  t6 -- NO --> a1
  t6 -- YES --> r1
  a4 -- YES --> t5
  t5 -- NO --> a1
  t5 -- YES --> r1
  a3 -- NO ---> w1
  a4 -- NO --> w2

  class r1 Event_Protection
  class w1 Event_Warning
  class w2 Event_Warning

1.1.2. Cell Voltage Protection Release

When BMS protect the system, protection action will be keep until release conditions occurred.

Diagram.1.1.2: Cell Voltage Protection Release

flowchart TB

  classDef Event_Release fill:green,color:white,font-weight:bold,stroke-width:0px
  classDef Event_Protection fill:red,color:white,font-weight:bold,stroke-width:0px
  classDef Event_Warning fill:yellow,color:black,font-weight:bold,stroke-width:0px

  a1[Under Cell Voltage </br>Protection Error Occured?]
  a2[Over Cell Voltage </br>Protection Error Occured?]

  a3(Cell Below  </br>O.V.P Release Voltage?)
  a4(Cell Higher </br>U.V.P Release Voltage?)

  r1([Keep Protection Action])
  r2([Release Protection Action])
  r3([Measure and Check Cell Voltages])

  a1 -- YES --> a4
  a2 -- YES --> a3
  a1 -- NO --> r3
  a2 -- NO --> r3

  a4 -- NO --> r1
  a3 -- NO --> r1

  a3 -- YES --> r2
  a4 -- YES --> r2

  class r1 Event_Protection
  class r2 Event_Release

1.1.3. Cell Balance

A good BMS should be capable of balance of each cell in series. But balance sequence will need a few parameters to start and stop balancers. To get highest capacity efficiency from battery pack, all cells need to be same voltage level.

Danger

Many of our BMS solutions have space for cooling balance resistors. User must be decide to proper settings to avoid excessive heating of PCB.

Diagram.1.1.3: Cell Balance

  flowchart TB

    classDef Event_Release fill:green,color:white,font-weight:bold,stroke-width:0px
    classDef Event_Protection fill:red,color:white,font-weight:bold,stroke-width:0px
    classDef Event_Warning fill:yellow,color:black,font-weight:bold,stroke-width:0px

    a1[Measure and Check Cell Voltages]
    a2[is Balance Restricted?]
    a3[Did Balance Method Condition Match?]
    a4[is Cell Voltage Over Threshold?]
    a5([Start Balance From Highest Cell Voltage])
    a6[is Cell Voltage Higher Than Start Delta?]
    a7[is Cell Voltage Below Stop Delta?]

    a8[Set Balance Duty Cycle and Check Number Of Simultaneous Cell Count]

    r0([Do Nothing])
    r1([Finish Balance]) 

    a1 --> a2 -- NO --> a3 -- NO --> r0
    a2 -- YES --> r0
    a3 -- YES --> a4 -- NO --> r0
    a4 -- YES --> a6 -- YES --> a5 --> a8 --> a7 -- NO --> a8
    a6 -- NO --> r0
    a7 -- YES --> r1     

    class r0 Event_Release
    class r1 Event_Release
    class a5 Event_Protection

1.1.4. Unbalanced Maksimum Cell Delta

Sometimes because of cell aging or manufacturing process error, some of cell(even if one of them) in the battery pack could cause safety issues. Cell's conditions drifts on time against others and it causes dangerous situations. Cell voltage is the first of many parameters.

Diagram.1.1.4: Unbalanced Maksimum Cell Delta

  flowchart TB

    classDef Event_Release fill:green,color:white,font-weight:bold,stroke-width:0px
    classDef Event_Protection fill:red,color:white,font-weight:bold,stroke-width:0px
    classDef Event_Warning fill:yellow,color:black,font-weight:bold,stroke-width:0px

    a1[Measure and Check Cell Voltages]
    a2[is Cell Voltage Higher Than Maksimum Cell Delta?]

    a1 --> a2 -- YES --> r1
    a2 -- NO --> a1

    r1([Do Immediate Protection Action])

    class r1 Event_Protection

1.1.5. Maksimum Parallel Group Delta

Our BMS solution is capable of control parallel lithium battery packs. While operating as parallel, this must be a huge dangerous situation.

Diagram.1.1.5: Maksimum Parallel Group Delta

flowchart TB

    classDef someclass fill:#f96
    classDef Event_Release fill:green,color:white,font-weight:bold,stroke-width:0px
    classDef Event_Protection fill:red,color:white,font-weight:bold,stroke-width:0px
    classDef Event_Warning fill:yellow,color:black,font-weight:bold,stroke-width:0px

    a1[Measure and Check Parallel Battery Voltages]
    a2[is Battery Voltage Higher Than Maksimum Cell Delta?]

    a1 --> a2 -- YES --> r1
    a2 -- NO --> a1

    r1([Do Immediate Protection Action])

    class r1 Event_Protection