6.1 Events and What to Do

You see an event in LiMon™, or an event bit on CAN or Modbus, and you want to know what to do about it. This page gives the likely cause of each event, what to check and what to do. What each class of event does to the paths is explained in 5.1; this page is about finding and fixing the cause.

Applies to

Boards: BMS1820, BMS3610, BCU2002, BMS1601, BMS1810. Where an event comes from one board only, its row says so.

6.1.1 How It Works

Every event has a number, which is the same everywhere. Events › Event Status writes it in front of the name, and on CAN and Modbus it is the bit number; the error bit table and CAN frame 0x07 list every bit with its class. The rows below use the names on Events › Event Status. A few of these names differ from the table; 5.4 Logs and Event History lists them.

Fig.6.1.1: First Response to an Event

1 Read Events › Pack Status, or the event bits on CAN or Modbus 2 Save it screenshots of Fetch Logs before any restart 3 Find it Table.6.1.1 gives the section of the event 4 Active now? the colour of the mark and User Support Yellow mark all paths stay ON; act on the cause Red mark a path is OFF; fix the cause, it comes back by itself User Support red fix the cause, then restart the BMS Check no event comes back On CAN or Modbus the class of each bit is in the error bit table. A blue mark is an input, an output or a functional state, not a fault.

  • Read what is active: Events › Pack Status shows it, and # of Events in Live View counts it (5.2 Monitoring). A blue mark is not a fault.
  • Keep the record before you act: a restart ends what is active now and the trip counts. Take the screenshots of 5.4 Logs and Event History first.
  • What the event does: 5.1 Protection and Recovery explains which path switches OFF, when it comes back, Error Recovery Attempts and User Attention Required.
  • Settings: this page has no settings of its own. Each section names the page that holds its settings.

Table.6.1.1: Find the Event

Event numbers Marks on Pack Status Section
7 to 11, 19, 20 Cell O.V.P, Cell U.V.P, Max. Cell V Delta, Low SOC 1st, Low SOC 2nd 6.1.2 Cell Voltage and SoC
1 to 6, 12, 21 to 24, 38 Pack O.T.P., DCHG U.T.P., CHG U.T.P., Max. Temp. Delta, PCB O.T.P., FET O.T.P., Balance Temp 6.1.3 Temperature
13 to 18 DCHG O.C.P., DCHG 2nd O.C.P., CHG O.C.P., Short Circuit 6.1.4 Current
26, 29 Cell Connection, Slave Comm. 6.1.5 Cell and Module Connections
30, 31, 36, 37 MAIN Cont. Error, PCHG FAULT, CHG Cont. Error, DCHG Cont. Error 6.1.6 Contactors and Precharge
28, 33, 34, 35 Max. Group Delta; 33 to 35 have no mark 6.1.7 Parallel Groups and Parallel Packs
0, 27, 32 User Support, SYS Initialize; 27 has no mark 6.1.8 Status Events

6.1.2 Cell Voltage and SoC

The limits are in 3.3 Cell Voltage Limits, the SoC in 3.2 Capacity and SoC, the balancing in 3.4 Cell Balancing. Vcell Max, Vcell Min and Vcell Delta in Live View cover the whole pack, so read them first and then find the cell in the chart of each module.

Table.6.1.2: Cell Voltage and SoC Events

Event Likely cause What to check What to do
(8) Cell Over Voltage Warning Limit Exceeded The charger voltage is high for the cells, or one cell runs above the others. Vcell Max and which cell it is; the charger voltage per cell; Vcell Delta. Lower the charger voltage, or give the balancing time. A warning at the end of every normal charge can also mean that O.V. Warning is set too close to your charge voltage.
(7) Cell Over Voltage Protection Limit Exceeded The same, and the charge went on until a cell passed O.V. Protection. The same, and how often it has tripped (5.4). Stop the charger and fix the cause. The charge path comes back when the cells are at or below O.V.P Release. If a cell stays above it, see the recovery below.
(10) Cell Under Voltage Warning Limit Exceeded The pack is nearly empty, the load is heavy, or a cell is weak. Vcell Min under load, the SOC, and whether the same cell is always the lowest. Reduce the load or charge the pack.
(9) Cell Under Voltage Protection Limit Exceeded The same, and a cell passed U.V. Protection. The same, and how often it has tripped (5.4). Charge the pack. The discharge path comes back when the cells are at or above U.V.P. Release. A pack that is too low to recover this way: 5.3 Storage and Shutdown.
(11) Max. Cell Delta Voltage Protection Limit Exceeded A weak cell, a loose cell tap, or cells that have drifted apart. Vcell Delta and the cell chart; measure the suspect cell at its tap with a meter and compare. Fix a loose tap, then restart. If the cells really are apart, follow case 3 in 5.3 Storage and Shutdown. Replace a cell that keeps falling behind.
(19) Low SOC 1st Warning Limit Exceeded, (20) Low SOC 2nd Warning Limit Exceeded The SOC is at or below 15 % or 5 %. The pack is nearly empty, or the SoC reads wrong. SOC against Vcell Min: cells well above empty point to a wrong SoC. Charge the pack. No path switches OFF. If the SoC was wrong, check the capacity setting and charge to FULL.

A cell that stays above O.V.P Release. The charge path stays OFF, and a cell falls only when something draws from it. Disconnect the charger and check its voltage first, so that it does not raise the cells again. Then follow the case that fits your pack.

Case 1: separate discharge contactor, or BMS1601. The discharge path stays ON under this protection, so Clear All Errors is not needed. Connect a load and discharge until every cell that tripped is at or below O.V.P Release.

Case 2: one main contactor. The main contactor needs both paths ON, so the load cannot reach the pack (3.8 Power Path). Before you start, check these points:

  • User Button Functionality is set to Advanced Push Button.
  • A press is assigned to Clear All Errors, and the setting is saved; the default Long Press Function has it (3.11 Button and Shutdown).
  • The charger is disconnected.
  • A load that you can switch is connected and OFF. It should draw a steady current of several amperes, within what the cell datasheet allows. With the load OFF, the precharge at the start is not disturbed (3.9 Precharge).

Then run the recovery:

  1. Run Clear All Errors from the button. The BMS forces its outputs ON for 60 s, so the main contactor closes.
  2. Switch the load ON, and check that the current flows within these 60 s. Once the BMS sees the discharge, it does not open the path again. If no current has flowed, switch the load OFF and run Clear All Errors once more.
  3. Stay with the pack and watch Live View. When every cell that tripped is at or below O.V.P Release, switch the load OFF. The BMS does not end this discharge for you.
  4. Press Restart System with no load and no charger current. Then check that the paths switch ON and that no event comes back.

Not tried on a board yet

This recovery mirrors the low-cell recovery of 5.3 Storage and Shutdown and has not been tried on a board yet. Watch the current when the 60 s end, and keep a way to disconnect the load.

Clear All Errors on a high pack

Clear All Errors overrides the protections for 60 s, so a connected charger would push the high cell further up. Until the restart in step 4, the BMS keeps the discharge path ON, so a load left connected goes on draining the pack. Never use this on a temperature or a contactor fault.

6.1.3 Temperature

The limits are in 3.5 Temperature Limits. Max Ext. Temp. and Ext. Temp. Delta in Live View cover the whole pack; T1 to T5 and PCB Temp follow the selected module, so select each module in turn.

Table.6.1.3: Temperature Events

Event Likely cause What to check What to do
(2) Over Temperature Warning Limit Exceeded, (1) Over Temperature Protection Limit Exceeded A hot place, a closed box with little air flow, a high current for a long time, or a sensor close to a busbar or a power cable. Max Ext. Temp., which sensor it is, the air flow and how the sensor is mounted. Reduce the current and let the pack cool. After (1), both paths come back at Over Temp. Release. Improve the cooling, or move a sensor that reads its surroundings instead of the cells.
(6) CHG Under Temperature Warning Limit Exceeded, (5) CHG Under Temperature Protection Limit Exceeded A cold place, and a charge into a cold pack. T1 to T5 on each module. Warm the pack before charging. After (5), the charge path comes back at CHG. U.T.P. Release. Do not lower the limits below the cell datasheet.
(4) DCHG Under Temperature Warning Limit Exceeded, (3) DCHG Under Temperature Protection Limit Exceeded A cold place, and a discharge from a cold pack. T1 to T5 on each module. Warm the pack. After (3), the discharge path comes back at DCHG. U.T.P. Release.
(12) Max. Temperature Delta Protection Limit Exceeded A loose or fallen sensor, a badly placed sensor, or local heating in one part of the pack. Ext. Temp. Delta; which sensor stands apart; its mounting. Feel or measure that part of the pack. Refit the sensor, or find the cause of the heating, then restart. Temperature Max. Delta gives no warning first (5.2 Monitoring).
(21) PCB Over Temperature Warning Limit Exceeded, (22) PCB Over Temperature Protection Limit Exceeded A closed box, or the heat of the balancing on the board. PCB Temp on each module, the air around the boards, and the balancing marks in the cell chart. Improve the air flow, and lower Balance Duty Cycle or Simultaneous Balancing Cells. After (22), both paths come back at PCB O.T. Release.
(23) FET Over Temperature Warning Limit Exceeded, (24) FET Over Temperature Protection Limit Exceeded (BMS1601) A high current for a long time, or too little cooling. Pow. Path Temp, the current and the cooling of the board. Reduce the current and improve the cooling. After (24), both paths come back at FET O.T. Release.
(38) Balance Progress Over Temp. Warning A closed box, or a high balancing load. PCB Temp against Cell Balance O.T. Warning. No path switches OFF, but balancing stops until the board has cooled. Lower Balance Duty Cycle or Simultaneous Balancing Cells, or improve the air flow (3.4 Cell Balancing).

6.1.4 Current

The limits are in 3.7 Current Limits, the measurement in 3.6 Current Measurement. The BMS compares its limits with the current it measures, so check that reading first.

Table.6.1.4: Current Events

Event Likely cause What to check What to do
(13) DCHG Over Current Warning Limit Exceeded, (14) DCHG Over Current Protection Limit Exceeded, (15) DCHG Over Current 2nd Protection Limit Exceeded The load draws more than the limit, or the current reads too high because of a wrong coefficient. Current against a meter on the pack cable, and the load at that moment. Reduce the load, or correct Current Sensor Ch#1 Coeff. or Current Sensor Ch#2 Coeff. After (14) or (15), the discharge path comes back after its release time.
(16) CHG Over Current Warning Limit Exceeded, (17) CHG Over Current Protection Limit Exceeded The charger gives more than the limit, or a motor feeds current back into the pack. Current against a meter, the charger setting, and whether the event comes while the motor brakes. Lower the charger current or the current fed back. After (17), the charge path comes back after its release time.
(18) Short Circuit Protection Limit Exceeded A short circuit on the load side, or the inrush of an inverter with no precharge. The load cables, the fuse and the load, before anything switches ON again. Disconnect the load first: both paths come back by themselves after the release time. Repair the short, then set up the precharge if the load is an inverter (3.9 Precharge).

6.1.5 Cell and Module Connections

The settings are in 3.1 Battery Topology. Both events keep both paths OFF until a restart, even after the cause is fixed.

Table.6.1.5: Connection Events

Event Likely cause What to check What to do
(26) Cell Connection Error A broken or loose cell tap, a wrong cell count in the settings, an unused input that is not wired as 3.1 describes, or a cell that has fallen so low that it reads as not connected. Connected Cells on each module: the two numbers differ on the faulty one. Find the cell in the chart, and measure it at its tap with a meter. Repair the tap, or correct the cell count and save, then restart. A pack with a real low cell: 5.3 Storage and Shutdown.
(29) Slave Module Communication Error A faulty daisy chain cable or connector, a slave module that gets no supply from its own cells, or a wrong Board ID. The module list in Live View: which module is missing. Then its daisy chain cable, its connectors and its cell voltages. Repair the cause, then restart.

6.1.6 Contactors and Precharge

The contactors are in 3.8 Power Path, the auxiliary inputs in 3.10 Inputs and Outputs, the precharge in 3.9 Precharge.

A welded contactor

Paths that read OFF do not prove that the contact is open. If a contact may be welded, treat the output terminals as live until you have measured them.

Table.6.1.6: Contactor and Precharge Events

Event Likely cause What to check What to do
(30) Main Contactor Malfunction; (36) Charge Contactor Malfunction, (37) Discharge Contactor Malfunction (BMS1810) No coil supply, a wiring fault, a welded contact, or a normally closed auxiliary contact. Measure the coil voltage while the OUT mark is blue, and the contact itself. Check the wire to the input with Main Contactor Auxiliary, CHG Contactor Auxiliary or DCHG Contactor Auxiliary. Repair the wiring, or replace the contactor or use a normally open contact, then restart.
(31) PreCharge Error A shorted load, a load that is already ON, a Pre-Charge Time that is too short, a running charger, or a current that flowed when the BMS started. Disconnect the load and check it. Then the sizing and Pre-Charge Current Limit. Follow the recovery in 3.9 Precharge, and restart with no current flowing.

6.1.7 Parallel Groups and Parallel Packs

Event (28) belongs to the parallel groups of one pack on BMS1810, described in 3.1 Battery Topology. Events (33) to (35) belong to parallel packs in Multi-Master mode, set up in 4.3 Parallel Packs. They have no mark on Pack Status, so read them in Events › Event Status or from the event bits. The settings are in 7.6 Interface Settings.

Table.6.1.7: Parallel Group and Multi-Master Events

Event Likely cause What to check What to do
(28) Max. Parallel Group Delta Voltage Protection Limit Exceeded (BMS1810) The groups were connected at different charge levels, or a connection in one group is open. V-Total of the modules in each group, and the connections of the group. Bring the groups to the same voltage, repair the connection, then restart.
(33) M.M. Enable PowerOut Sequence On a pack set to MM Slave in Parallel or MM Slave in Series, both paths stay OFF until the main controller allows them. A short time at every start is normal. If it stays: whether the main controller is running, its own events, and the CAN link between the packs. Fix what holds the main controller back. The paths come back when it allows them.
(34) M.M.Communication Timeout Error The packs have lost contact: a faulty CAN cable or termination, the main controller is off, or the setup does not match. The CAN wiring and termination, that each pack has its own CANBus CH#1 Base Frame ID, and that Multi Master Slave Units on the main controller matches the number of slaves. Fix the cause. If the event stays after that, restart. MM Comm Error Strategy decides what happens to the power outputs.
(35) M.M. Parallel Packs Delta Voltage Error A slave pack is Pack Delta Voltage Protection or more away from the average of the slave packs; the main controller's own pack is not compared. Pack Voltage of each pack. Separate the packs and bring each one to the same voltage, then connect them again. If the event stays after that, restart. MM Delta Protection Strategy decides what happens to the power outputs.

6.1.8 Status Events

These events report a state of the BMS. They switch off no path by themselves.

Table.6.1.8: Status Events

Event What it means What to do
(0) User Support Need The BMS will not recover by itself: a CRITICAL fault is present, or a protection has used up Error Recovery Attempts. Find the other event that came with it in this page, fix the cause and restart (5.1 Protection and Recovery).
(27) Sleep Function Error A shutdown was requested while faults held both paths OFF. It is not a fault itself, and the shutdown still happens. Read the other rows around it in the history: they show why the paths were OFF.
(32) System Initialize The BMS has started. It shows for a short time at every start, and leaves two rows in the history. Nothing. These rows mark each start (5.4 Logs and Event History).

6.1.9 Checking the Result

  • # of Events in Live View is 0, or shows only what you expect, and User Support is grey.
  • CHG PATH and DCHG PATH are ON, except where an input holds them OFF on purpose (5.2 Monitoring).
  • Connected Cells shows two equal numbers on every module, and every module is listed.
  • After the next normal cycle, press Fetch Logs: the event has not come back since the last (32) System Initialize.
  • The limits that you changed for a recovery are back at your values.

6.1.10 Common Mistakes

  • Restarting before reading. The restart ends what is active now and the trip counts. Take the screenshots first.
  • Changing a limit to make an event go away. The limit protects the cells. Find the cause first, and set the limits from the cell datasheet.
  • Treating a warning as noise. A warning that comes back at the same load, or earlier than before, announces a protection.
  • Looking only for the red mark. User Support says that the BMS needs you, not why. The other event says why.
  • Not trusting the meter. The current events act on the current the BMS measures. A wrong coefficient, or a current that flowed at the start, looks like a real over current.
  • Switching a load back on after a Short Circuit event without checking it. The BMS retries after the release time. Disconnect the load until the short is repaired.
  • Clear All Errors used to get past an event. It forces the outputs ON for 60 s, and it never clears a CRITICAL event. The two recoveries for a pack that is too low or too high are the only uses on a pack with a cell event.