4.2 Monitoring
This page shows how to read a running battery: what a healthy pack looks like at rest, while charging and while discharging, which values announce trouble before a protection trips, and what to do when LiMon™ stops updating. It explains how to read the values; the LiMon™ reference lists every field of every screen.
Applies to
Boards: BMS1820, BMS3610, BCU2002, BMS1601, BMS1810.
4.2.1 How It Works
While LiMon™ is connected, the BMS sends its values regularly and the screens update by themselves. Live View shows the state of the pack at this moment. It stores nothing and changes nothing, and it pauses for a short time while LiMon™ reads the settings. The LiMon™ reference describes every field of the screen: 4. Live View.
Fig.4.2.1: The Areas of Live View and What Each One Tells You
- Whole pack or one module. Pack Voltage, Vcell Max, Vcell Min, Vcell Delta, Max Ext. Temp. and Ext. Temp. Delta cover the whole pack. The cell chart, Connected Cells, V-Total, T1 to T5, PCB Temp and Pow. Path Temp follow the module you select in the list.
- Sign. Current and Power are + while charging and − while discharging.
- Steps. Pack Voltage moves in steps of 0.1 V, Current in steps of 0.1 A and SOC in whole percent.
- No current. A current between −0.5 A and +0.5 A reads as no current, and Battery Power shows IDLE (3.6 Current Measurement).
4.2.2 Reading Live View
Read the state first, then the values. Table.4.2.1 shows a healthy pack without active events.
Table.4.2.1: A Healthy Pack in Live View
| Field | At rest | Charging | Discharging |
|---|---|---|---|
| Battery Power | IDLE | CHARGING | DISCHARGING |
| Current, Power | 0.0 A, no power | positive | negative |
| Pack Voltage | steady | rises | falls, and is lower under load |
| SOC, Energy | steady; fall only slowly | count up | count down |
| Vcell Max, Vcell Min | steady, inside the warning limits | rise, inside the warning limits | fall, and are lower under load |
| Vcell Delta | about as low as your earlier readings | can grow near the end of the charge and falls while the cells balance | can grow near the end of the discharge |
| T1 to T5, Max Ext. Temp. | close to the surroundings | rise with the current | rise with the current |
| CHG PATH, DCHG PATH | ON | ON | ON |
| PCHG PATH | OFF | OFF | OFF; ON for a short time when the discharge path switches on |
| # of Events | 0 | 0 | 0 |
| Connected Cells | two equal numbers | two equal numbers | two equal numbers |
At rest
- Current: a reading other than 0.0 A at rest usually comes from a current that flowed when the BMS started (3.6 Current Measurement). A large Self Discharge Power can show −0.1 A, which is not a fault.
- SOC: it falls only as far as Self Discharge Power predicts (3.2 Capacity and SoC).
- Balancing marks: a red circle around a cell number means that the cell is balancing. Balancing Method decides in which state this can happen, so with While Charging there are no marks at rest (3.4 Cell Balancing).
While charging
- Battery Power shows CHARGING from 0.5 A upward. A smaller charger current stays IDLE and the SOC does not count it.
- SOC stops at 99 % with Hold %99 until FULL SoC on, and goes to 100 % when the FULL conditions are met.
- Vcell Delta shows the real differences between the cells best near the end of the charge, and this is where the balancing marks usually appear.
While discharging
- Vcell Min is lower under load than at rest. Compare it with U.V. Warning under your usual load.
- PCHG PATH is ON only for a short time when the discharge path switches ON, with DCHG PATH OFF during that time (3.9 Precharge).
Paths and modules
- A path that is ON is allowed, not in use. Battery Power and Current show what really flows.
- Paths can be OFF on a healthy pack. With CHG Power Path Interlock the charge path is OFF until the connector is plugged in, and the discharge path is OFF while it is plugged in. An input with DCHG Power Path Disable or Battery Output Disable also holds paths OFF (3.10 Inputs and Outputs).
- Module list: it shows the modules that send data to LiMon™. Select each one and check its Connected Cells (3.1 Battery Topology).
- Pow. Path Temp reads 0 on a board without that sensor, and -- at T1 to T5 means that the sensor gives no reading.
4.2.3 Routine Checks
After commissioning, note the values of the healthy pack: a full charge at rest gives a point you can always return to. Compare with this record regularly. The numbers that are normal depend on your cells and your settings, so the table compares each value with your own record and your own limits.
Two values give no warning
Vcell Delta and Ext. Temp. Delta have no warning event. When one of them reaches its limit, Imbalanced Max. Cell Delta or Temperature Max. Delta, the BMS switches off both paths until a restart (4.1 Protection and Recovery). Only your own comparison shows them growing.
Table.4.2.2: Routine Checks
| What to look at | Normal | Warning sign | Described in |
|---|---|---|---|
| # of Events, Events › Pack Status | 0; no yellow or red | Any yellow or red mark. A warning that comes back at the same load, or earlier than before. | 4.1, 4.2.4 |
| Vcell Delta, at the end of a full charge at rest | As in your record, and well below Imbalanced Max. Cell Delta | It grows from charge to charge, or balancing no longer brings it down. | 3.4 |
| Cell chart, every module | No cell stands out | The same cell is always the lowest or the highest. | 3.4 |
| Vcell Max, Vcell Min, under your usual load | Inside O.V. Warning and U.V. Warning | They come closer to the warning limits than before at the same load and SoC. | 3.3 |
| T1 to T5, Ext. Temp. Delta | The sensors stay close together and follow the load and the surroundings | One sensor drifts away from the others at the same load, the delta grows towards Temperature Max. Delta, or a sensor that gave a reading now shows --. | 3.5 |
| PCB Temp, Pow. Path Temp | Below PCB O.T. Warning and FET O.T. Warning | They run warmer than before at the same load; the Balance Temp mark on Events › Pack Status turns yellow while balancing. | 3.5, 3.4 |
| SOC, Energy | They count smoothly and reach 100 % at the end of a full charge | A large jump at FULL or EMPTY, a jump to 100 % or 0 % away from the ends, or a SoC that stays at 99 %. | 3.2 |
| Current, at rest | 0.0 A | Any other reading with no load and no charger, except the −0.1 A that a large Self Discharge Power can show. | 3.6 |
| Module list, Connected Cells | Every module is listed, with two equal numbers | A module is missing, or the numbers differ. | 3.1 |
The BMS corrects the SoC at FULL and at EMPTY, so a small jump there is normal. After a sudden loss of power the SoC can also return to a value that the BMS saved some time earlier; a restart or a shutdown saves it first.
4.2.4 Events › Pack Status and Event Status
# of Events in Live View says how many warnings and errors are active. Events › Pack Status shows which ones. Each mark is one event or one input or output, and its colour is the state at this moment. The LiMon™ reference lists every mark: 6.1 Pack Status.
Table.4.2.3: Colours on Pack Status
| Colour | Meaning | Counted in |
|---|---|---|
| Grey | Not active | Total Running |
| Yellow | Warning active | Total Warnings |
| Red | Protection or fault active | Total Errors |
| Blue | Input or output active, or a functional state | Total I/O Events |
- # of Events is Total Warnings plus Total Errors. Blue marks do not count, and they are not faults.
- One mark, two colours. A mark such as Cell O.V.P is yellow for the warning and red for the protection. Hover over a mark to see its full name.
- User Support in red is User Attention Required (4.1 Protection and Recovery).
- Paths: the charge and discharge path are not on this screen; read them in Live View. PreCHG Stage is blue during a precharge, and DCHG Force OFF is blue while an input holds the discharge path OFF.
- Inputs: INPUT-1 to INPUT-3 are blue while the input is active.
- Outputs: OUT-1 to OUT-8 are blue while the BMS commands the output ON. A mark shows the command, not the contactor: only an auxiliary input such as Main Contactor Auxiliary checks the real contact (3.8 Power Path). Marks of outputs that a board does not have stay grey.
- Only what is active now. A mark goes grey when its event clears, so a protection that released by itself leaves nothing on this screen.
Events › Event Status answers what happened earlier. It is not a live view: after Fetch Logs it lists the events stored in the BMS, each as detected or cleared and with its time, and it does not change until you fetch again. Reading this list belongs to 4.4 Logs and Event History; the fields are in 6.2 Event Status. With a VIEWER licence this tab is locked, and Pack Status still works.
4.2.5 Monitoring Over CAN and Modbus
A controller or a display can read the same values without LiMon™. The signs are the same, and Table.4.2.2 applies to these values too.
- CAN: with the LiBat v2.x protocol the BMS sends the SoC, the cell minimum, maximum and delta, the current, the path states, the power, the temperatures and the event bits, and each module's cells and sensors. See LiBat v2.x Data Frames.
- Modbus: the registers give the pack voltage, current and SoC, the lowest and highest cell and temperature, and the event bits. The cells and sensors can be read one module at a time. There is no delta register, so subtract the lowest cell from the highest. See the Register Map.
- Events: the event bits are active events, as on Pack Status, with their classes in the error bit table.
- Inputs and outputs: the INPUT and OUT marks are in LiMon™ only.
- Lost data: treat missing frames or an unanswered request as lost data, not as the last value still being true.
4.2.6 No Connection or Stale Values
The field at the bottom of the LiMon™ menu shows the connected port or Not Connected. The connection steps and fields are in 5. Connection.
- Not Connected: LiMon™ has no open port. On the Connection screen, refresh the list, select the port and click Connect.
- The port is connected, but the device fields stay on loading...: LiMon™ gets no valid answer from the BMS. Check that the BMS is ON and has not shut itself down (3.11 Button and Shutdown), then the cable, the INT201 adapter and its driver, and the port number.
- The values stop changing: when the data stops, LiMon™ keeps the last values on the screen, and they are no longer the state of the pack. The module list empties first. After a short time LiMon™ warns Timeout. You're not receiving data for a while., closes the port and shows Not Connected. Connect again and wait for new values before you trust the screen.
- The status shows DEMO: the Demo port is selected and the values are simulated.
4.2.7 Checking the Result
- The port is shown, and the values change: Current follows the load, and the charts move.
- Current agrees in size and sign with a meter on the pack cable.
- The sum of V-Total over all modules agrees with Pack Voltage, except on a BMS1810 with parallel groups.
- Connected Cells shows two equal numbers on every module.
- # of Events in Live View equals Total Warnings plus Total Errors on Pack Status.
4.2.8 Common Mistakes
- A Live View value read as a stored setting. Live View shows only present values. The settings are on the Settings tabs and can differ: Initial SoC, for example, shows the last value entered, and the present SoC is SOC in Live View.
- SoC expected to move at rest. With no current it falls only as Self Discharge Power predicts, and a load below 0.5 A is not counted at all. A SoC that stands still at rest is normal.
- CHG PATH ON read as charging. ON means that the path is allowed. Battery Power and Current show what flows.
- An OUT mark read as the real contactor state. The mark shows the command. A contactor that did not close, or a broken wire, looks the same on this screen. Measure it, or wire an auxiliary contact to an input with Main Contactor Auxiliary.
- # of Events read as a history. It counts what is active now, and it goes back to 0 when the events clear. Fetch the logs to see what happened.
- A blue mark read as a fault. Blue is an active input, output or functional state.
- Vcell Delta compared at different points. The difference changes with the load and the state of charge, so a value under load against a value at rest says nothing. Compare at the same point each time, for example at the end of a full charge at rest.
- Module values read as pack values. PCB Temp, Pow. Path Temp, the cell chart and T1 to T5 change with the selected module. A cell problem on another module stays out of sight in the chart; Vcell Max, Vcell Min and Vcell Delta show it.
- A stale screen after a lost connection. The last values stay on the screen, also those of a pack that has since tripped or shut down. Check the port field first.
- Demo values read as real. Check that the status shows your port, not DEMO.