Watchmon Critical Error while charging

Troubleshooting
1

The battery I’m charging throws a critical error
I’m using Canbus native 2.0 protocol and via my app I have logged the critical and charging flags coming from the watchmon. This is on a 44V battery pack.

Log

CriticalFlag: 1 ChargeFlag: 1 DchgFlag: 1 HeatFlag: 0 CoolFlag: 0 CellBFlag: 0
Current: 45.44 Charger Voltage: 50.38 Shunt Voltage: 49.50 Status: 1
CriticalFlag: 1 ChargeFlag: 1 DchgFlag: 1 HeatFlag: 0 CoolFlag: 0 CellBFlag: 0
Normal Phase: Voltage present, Current within limits, Staying ON
CriticalFlag: 3 ChargeFlag: 3 DchgFlag: 1 HeatFlag: 0 CoolFlag: 0 CellBFlag: 0
CRITICAL ERROR 1

Critical Flags bit 0 & 1 are set.

From the native canbus 2.0 documentation "WatchMon - Canbus Native 2.0 messages " pdf
critical control flags, Bit 0 is OK state (relay state) , bit 1 is Transistion of state, and bit 2 is precharge.

What does bit 1&2 mean?

The C code I’ve inherited errors on any flag set other than bit 0.

In the toolkit app no fields are highlighted in yellow to indicate an error

The tookit app did produce an snap shot which does refer to a critical error as below, but doesn’t seem to say what caused it.

===========================================================================
System 1690 - SYS1690
WatchMon1690
TimeStamp 7/2/2025 11:56:21 PM

System status information
Device Time Startup
7/3/2025 10:50:48 AM 7/1/2025 9:23:40 AM

SupplyVolt Ambient WifiSignal%
12.07v 24ºC Offline

Versions Hardware Firmware Software SerialNo
14.6 14.4.88 2.17.57 446913609

OpStatus AuthMode CMU Mode
Idle Default Normal

SysFaults: Nil

Live status information
Min @ ID Max @ ID Avg Repeat
CellVolt 4.00v @ 12 4.02v @ 1 4.01v 416
CellTemp 22ºC@ 1 23ºC@ 9 22ºC
BypassAmp 0.00A @ 0 0.00A @ 0
BypassTemp 27ºC@ 9 28ºC@ 1
BypSession 0.0mAh@ 0 0.0mAh@ 0

            Total Overdue  +Final  +Initial  InBypass

NumOfCells 12 0 0 0 0

             SoC%     Temp     Volt      Amp

Shunt 100.0% 38ºC 48.43v -0.019A

               ToEmpty    ToFull

Nom Capacity 273.986 0.014
Est Duration 33.8d 01:51
Recent Consume 0.020 0.008

Expansion board

Critical logic
control BattOK state
status OK

Charging logic
control ON state
Idle Bypass: off
status OK

Discharging logic
control ON state
status OK

Thermal Heating Logic
control OFF state
status OK

Thermal Cooling Logic
control OFF state
status OK

Remote Logic
ActV ActA TgtV TgtA state
Charge 0.00v 0.00A 50.30v 328.80A ON state
Dischg 0.00v 0.00A 40.80v 400.00A ON state

Daily Session information
Min Max
CellVolt 3.62 4.05
Thermal 12 23
ShuntSoc 57.5 102.0
ShuntVolt 43.75 48.79
SupplyVolt 12.00 12.04
Critical Events 1

            Charge    Dischg

ShuntPeak 47.09 0.00
Cumulative 121.452 0.166

Banding(hr) A B C D E F G H
SoC% 1.1 0.6 0.6 8.5 0.0 0.0 0.0 0.0
Thermal 0.0 0.0 0.0 0.0 2.0 8.8 0.0 0.0

Cell Node information
ID MinV MaxV MaxT BypT DatEr Reset RepCV
1 4.02v 4.02v 22°C 28°C 0 0 31
2 4.01v 4.01v 22°C 28°C 0 0 31
3 4.02v 4.02v 22°C 28°C 0 0 33
4 4.02v 4.02v 22°C 28°C 0 0 33
5 4.02v 4.02v -40°C 28°C 0 0 33
6 4.02v 4.02v -40°C 28°C 0 0 33
7 4.02v 4.02v -40°C 28°C 0 0 33
8 4.01v 4.01v -40°C 28°C 0 0 31
9 4.02v 4.02v 23°C 27°C 0 0 33
10 4.02v 4.02v 23°C 27°C 0 0 33
11 4.02v 4.02v 23°C 27°C 0 0 17
12 4.00v 4.00v 23°C 27°C 0 0 31

Bypass related information
ID Bypass Initial Session Amp

Cell Node setup
ID HiT HiBypT LoV Hi(V) BypV BypA CalV Serial HwVers
1 55°C 60°C 2.70v 4.23v 4.17v 0.60A 0 413461205 HW9.0 FW0.7 BL160.15
2 55°C 60°C 2.70v 4.23v 4.17v 0.60A 0 413461205 HW9.0 FW0.7 BL160.15
3 55°C 60°C 2.70v 4.23v 4.17v 0.60A 0 413461205 HW9.0 FW0.7 BL160.15
4 55°C 60°C 2.70v 4.23v 4.17v 0.60A 0 413461205 HW9.0 FW0.7 BL160.15
5 55°C 60°C 2.70v 4.23v 4.17v 0.60A 0 413461205 HW9.0 FW0.7 BL160.15
6 55°C 60°C 2.70v 4.23v 4.17v 0.60A 0 413461205 HW9.0 FW0.7 BL160.15
7 55°C 60°C 2.70v 4.23v 4.17v 0.60A 0 413461205 HW9.0 FW0.7 BL160.15
8 55°C 60°C 2.70v 4.23v 4.17v 0.60A 0 413461205 HW9.0 FW0.7 BL160.15
9 55°C 60°C 2.70v 4.23v 4.17v 0.60A 0 413461205 HW9.0 FW0.7 BL160.15
10 55°C 60°C 2.70v 4.23v 4.17v 0.60A 0 413461205 HW9.0 FW0.7 BL160.15
11 55°C 60°C 2.70v 4.23v 4.17v 0.60A 0 413461205 HW9.0 FW0.7 BL160.15
12 55°C 60°C 2.70v 4.23v 4.17v 0.60A 0 413461205 HW9.0 FW0.7 BL160.15

===========================================================================

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Any help appreciated.

Thanks
Graeme

2

can we have sum details about your battery
number of cells
cell chemistry
recommended charge voltage / current etc

3

Hi. Thanks for replying.
Battery is 2 of these in parallel, balancing wires from battery are connected in parallel via fuses to the batrium cellmate K9 and Watchmon Core.

Lithium, Nickel, Cobalt and Manganese.

These cells are nominally 44V. We’re currently using a 51V 42A power supply to charge them. It’s a configuration that we have inherited. We’ve found that it’s happy to supply 42A in current limit mode until the battery voltage reaches the PSU voltage. Although if the battery voltage gets too low it fails to charge them at all.

Recommendations for a proper charger are welcome as we intend to make dozens of these units.
I’ve noticed there are lot of 48V lithium chargers out there including Meanwell NPB 1700 - 48. It only has 25A charging capability though. Is this a suitable charger? I’m new to battery tech.

From Batrium software-
Cell bypass 4.17V
Nominal 3.7V
Low cell voltage 2.7V
Current Shunt Voltage 47.99V
Cell type is set to Lithium performance.

Thanks for your interest.
Graeme

4

Not wanting to put you off but your current configuration is the equivalent of arming a bomb.
NMC batteries are very dangerous if overcharged.
If one cell goes into thermal runaway you will have a fire that is very difficult to extinguish.

A popular charger is a flatpack2 module connected to the BMS over CAN bus
in this way the BMS can tell the charger what voltage/current to supply to the battery

Charging batteries in parallel like this is difficult and potentially dangerous.
if a single cell fails how are you detecting this
does the battery manufacture support connecting there product in parallel.

you need to go back to the battery manufacture and get more data on charging parameters

above 80% soc you need to radically reduce your charge current
as soon as the BMS goes into cell bypass mode you need to drop the charge current down to
a level where the cell voltages do not rise above the bypass voltage.