16-cell BMS

16-cell BMS

The goal of this BMS is to use mostly decade old components to create a 16 channel cell voltage meter. It uses a very accurate sigma/delta ADC for superb resolution. It can drain about 100mA from a cell or charge it with 50 mA via the DC/DC converter. The ability to both charge and discharge cells speeds up balancing despite the low balancing current.

On the low voltage side it features two inputs for temperature sensors and one input for a 5V current sensor, differential or single ended.

It can be cascaded to be used with more than 16 cells and has an automatic addressing scheme to forgo the use of jumpers or DIP switches. All communication is done via CAN. Supply voltage is 12V with about 20 mA draw when not balancing.

The software is not yet finished, see forum for progress

Pinout

The pinout is also written to the bottom silkscreen.

On the left side you see 17 inputs. The first one is connected to the negative pole (GND) of your (sub)pack, the subsequent ones to the positive poles of up to 16 cells. At least the lower two cell inputs must be connected. When cascading modules the positive-most input of module n is also the GND of module n+1, so must be spliced to connect to both.

On the top right is the vehicle interfacing or low voltage connector. From top to bottom it is low voltage GND, 12V, enable_in, enable_out, CANH, CANL. GND, 12V, CANH, CANL are connected to all modules in parallel whereas enable_out is chained to enable_in of the next module. The first enable_in must be connected to 12V whenever the BMS should become active, e.g. when charging or driving. The module with 12V on the enable_in auto-detects as "main" module, collects data from the subsequent modules and sends more high level CAN messages

On the bottom right is the temperature sensor and current sensor input. Top to bottom it is tsensor1+, tsenseor1-, tsensor2+, tsensor2-, 5V, CUR+, CUR-, GND. A single ended current sensor is just connected to CUR+.

Right now the current sensor is only supported on the main module and only one temperature sensor is supported.

Communication

All configuration, queries and firmware updates are done via the CAN bus. There is no independent web interface like known from e.g. the inverter. However there is a solution to connect an ESP32 via CAN and then have the known web interface or you can use Dave Fiddes "oic" tool for the command line. It is important to know that the main module has node-id 3 and the subsequent ones 3+i (i index of submodule, so 1st submodule has node-id 4). The base node id can be configured to start at something else than 3.

All info given here is preliminary and will likely change!

Apart from that the modules output periodic CAN messages depending on their role.

All modules output on ID 500 (0x1F4) + i

start	length	item	description
0	16	umin	minimum cell voltage of module i
16	16	umax	maximum cell voltage of module i
32	16	uavg	average cell voltage of module i
48	8	numchan	number of connected cells
56	8	temp	temperature reading of module i

In addition the main module outputs on id 300 (0x12C)

start	length	item	description
0	10	chargelim	maximum charge current in A
10	10	dischargelim	maximum discharge current in A
20	10	soc	Pack soc in 4*%
40	12	idcavg	Averaged current reading of last 1s
52	10	utotal	Total pack voltage in V

Reading individual cell voltages

Cell voltages are only available via CAN SDO from the module that measures them. So voltages 1-16 must be queried from the first (main) module, 17-32 from the 2nd (1st submodule) and so on. With Dave Fiddes tool this translates to:

oic -n 3 dumpall #dumps all values including cell voltages from 1st module
oic -n 4 dumpall #same for second module
oic -n 4 read u0 #Read first cell voltage of second module

For querying voltages say in your arduino sketch you'll need to acquire every voltage separately by sending and receiving SDO messages

0x603#0x40 idhigh 0x21 idlow 0 0 0 0

idhigh and low are the bytes of the internal ID. The id of the first cell voltage is 2006 (0x7D6) so for querying the 1st cell voltage of the first module you send

0x603#0x40 0x07 0x21 0xD6 0 0 0 0

And you will receive the reply

0x583#0x43 0x07 0x21 0xD6 0xD0 0xED 0x01 0

0x0001EDD0 is the voltage value which decodes to mV x 32. So 0x1EDD0/32 = 3950.5 mV.

The next cell would be on 0x7D7 and the last on 0x7E5. The next 16 voltages are then queried from node id 0x604.

Configuration Parameters

There is currently a limited set of parameters which will be extended as the software grows.

Name	Unit	Min	Max	Default	Description
gain	uV/dig	1	1000	586	Scaling factor from ADC digits to mV
numchan		1	16	16	Number of cells connected to the module
balance		0	1	0	Enable/Disable balancing function
idlewait	s	0	100000	60	Number of seconds to wait after stop of current flow to measure unloaded cell voltage
nomcap	Ah	0	1000	100	Nominal capacity
idcgain	dig/A	-1000	1000	10	Gain (or actually division factor) of current sensor
idcofs	dig	-4095	4095	0	0A offset
idcmode		0	3	0	Current sensor mode 0=Off, 1=Single Ended ADC, 2=Differential ADC, 3=ISA current shunt
tempsns		-1	3	-1	Temperature sensor -1=Off, 0=JCurve, 1=KTY81, 2=PT1000, 3=LeafBMS
pdobase		0	2047	500	base COB Id for cyclic messages. Main module uses pdobase, 1st submodule uses pdobase+1 and so on
sdobase		0	63	3	base node ID for SDO queries. Main module uses sdobase, 1st submodule sdobase+1 and so on