FLEX BMS
Software Version 0.6
Installation and Operations Guide
Applies to
BMS-36, BMS-48, BMS-60
1 Flex BMS Introduction
and Features
The Flex BMS provides a complete
Battery Management and Monitoring System solution for Lithium based electric vehicles.
 The Flex BMS-36 product is designed to support 18-36 cell Lithium-ion based
electric vehicles which are typically DC powered, highway capable vehicles (57v115v).

The Flex BMS-48 product is designed to support 37-48 cell Lithium-ion based
electric vehicles which are typically DC powered, highway capable vehicles
(118v-153v).

The Flex BMS-60 product is designed to support 49-60 cell Lithium-ion based
electric vehicles which can DC or AC powered systems, highway capable
vehicles (156v-192v).
The Flex BMS is not chemistry specific and can be programmed for almost any type of
Lithium chemistry cell. The Flex BMS supports LiFePO4 cells from 10Ah to 180Ah
capacity.
The Flex-BMS architecture has a centralized data collection system and a small dash
mounted display Console. The data collection system monitors the voltage on each
battery and provides a battery balancing function. The dash console provides a simple
user interface to provide the primary battery condition information to the user. The dash
Console does not have to be constantly monitored; it will provide display and audible
alerts when there is a battery problem or when batteries have reached their low voltage
point.
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The features of the Flex BMS are:
 Dash mounted status display, provides simple
viewing of battery system.
 Centralized monitoring of individual cell voltages, up
to 48 Lithium cells.
 Up to 2 external temperature probes, and an internal
temperature probe.
 Configurable Upper Voltage Threshold, Low Voltage
Threshold, and Balance Voltages
 Configurable temperature threshold for alerts.
 Automatic battery balancing, up to 1A per cell
 Integrated, isolated charger cutoff switch, up to 240V, 20A
 Balance at the end of each charge cycle and a separate Balance mode to
balance cycle the batteries.
 Fully isolated architecture requires no vehicle 12v power or connections to
controller components.
 Built-in logging function allows viewing of recent BMS activity and alerts.
What’s included with the Flex BMS:
 Central BMS Box
 Screwlock connectors for wiring harness connections
 2 temperature thermisters
 Display console
 12’ Cat-5 shielded cable
BMS Options:
 Current Monitor. Uses hall-effect sensor with ¾”
sensor opening that can be used with up to 2/0
cable. Allows installation without rewiring or new
current shunts. Current monitor show used KWh in
count-up mode or remaining KWh in count down
mode. Current monitor comes with a 4’ cable.

Data Logging Option. Uses internal USB stick to
log cell voltage, balance information and alerts
every minute. Logs errors as they occur. Data is recorded on a USB stick inside
the BMS Box. Data is in comma separated variable (csv) format that can be read
and analyzed using a spreadsheet program such as Excel. Data logging
formats are shown in Appendix C.

Note that wiring between the battery box and the batteries
is not included but can be ordered with the BMS.
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BMS 0.6d
Installation and Operations Guide
2 Flex BMS Installation
The Flex BMS architecture includes a centralized monitoring box and a remote dash
mounted display. The Flex BMS monitoring box needs to be protected from direct water
splashing and requires left to right venting. The monitoring box can be mounted inside
the vehicle compartment or in the vehicle trunk.
The monitoring box connects with the dash mounted display thru a 12 or 14-foot Cat-5
cable, provided with the Flex BMS. It is not recommended to exceed this cable distance.
Figure 1 below show the basic wiring configuration for the Flex BMS.
12' Cat5 cable
Dash
Console
BMS
System 144V
Status: OK
Console
Connector A
Connector
A to:
Cells 1-12 and
Temperature Sensors
TA and TB
Connector B
Connector
B to:
Cells 13-24
Connector C
Connector
C to:
Cells 25-36
Connector D
Connector
D to:
Cells 37-48 and
Temperature Sensors
TC and TD
Isolated 240V
Charger 25A
Relay
Charger Power Cutoff
Figure 1. BMS Vehicle Connections
BMS-36 provides 3 board connectors with the BMS.
BMS-48 provides 4 board connectors with the BMS.
BMS-60 provides 4 board connectors with the BMS.
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Installation and Operations Guide
16
15
5 4
3 2
1
Figure 2. BMS Board Connector pin identification.
Ref Digikey ED1972-ND
The BMS connects to the batteries using a wiring harness. The BMS has 3, 4, or 5
internal boards with connectors that allow a harness to be assembled and tested prior to
connection to the BMS boards. The BMS boards closest to the center of the box is
number 1, and the boards at the edge of the box are the highest numbed boards.
An example schematic for the Flex BMS system installation is shown in Figure 3 below.
The BMS 48 has 4 battery connectors 1, 2, 3 and 4. The BMS box contains 4 battery
connector sockets labeled 1, 2, 3, and 4. The connectors attach to separate isolated
boards. The #1 connector is for the lowest potential batteries, thru the #4 connector
which is for the highest potential batteries. It is recommend that battery groups be in the
order specified to aid in battery identification. Each of the other battery connectors can
be connected to between 6 and 12 batteries to monitor.
2 Temperature Sensors are available on Board #1. If unused, the Temperature Sensors
inputs can be left open.
Connection cable for the wiring harness between the BMS and the batteries is not
included. It is recommended to use 22, 24 or 26 gauge cable1. Use of multicolored
ribbon cable allows the easier identification of battery connections. Recommend
stripping and tinning the stranded ends with solder prior to screwlock in the green BMS
battery connector. Carefully check battery connections and polarity with a voltmeter prior
to connecting to the BMS box.
The charger cutoff relay is located inside the BMS box. Power cables are used for
charger power cutoff.
If a current monitor option is installed, a 5 pin DIN connector on the BMS box is used to
connect to the current monitor module. Connection cable is included with this option.
Install the current monitor anywhere in the battery current path.
A stand-by switch in included for long periods of BMS inactivity. The BMS consumes a
small amount of energy (about 25 mA) from the battery system for monitoring. When the
1
Recommend 3m 22 Ga 10 conductor Ribbon cable from Arrow Electronics. Part number 3319/10
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Installation and Operations Guide
BMS is not needed, put the stand-by switch into stand-by mode to save battery power.
After switching back to “ON”, Restart the BMS from the main menu.
.
“A”
Connector
Digikey
On-shore
ED1972-ND
A-15
A-14
A-13
...
A-16
A-7
A-6
A-5
A-4
A-3 A-2 A-1
Wiring
Harness
Allied:
3M 22ga x10
Rainbow Ribbon
+
+
...
Cell 12 Cell 11 Cell 10
-
Cell 3 Cell 2
Cell 1
TA: (optional) 10K
NTC Thermister
Mouser
871B57871S103F1
TB: (optional) 10K
NTC Thermister
Figure 3. BMS Battery Connection Schematic
If less than 12 batteries are connected on the #4 Connector, tie the unused highest
potential leads to the highest voltage on the system, as shown in Figure 4.
Figure 4. Partial use of #4 connector for a 46 Cell Configuration.
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BMS 0.6d
Installation and Operations Guide
3 Flex BMS Configuration
When the BMS is first started, it will perform diagnostics and then display the main
menu. Configuration is necessary prior to starting the monitoring program. The Flex
BMS is configured using the BMS console. Select is the rotary encoder on the BMS
Console, which can be rotated or pressed. Configuration settings are stored in nonvolatile EEPROM memory.
The following configuration settings are necessary prior operation and monitoring.
1. Configure number of cells to Monitor. BMS 48 with four monitoring boards can
monitor between 36 and 48 cells.
a. From the main menu rotate the Select knob until configuration is indicated
in brackets. The configuration menu is displayed. Rotate the Select knob
until “Config: is displayed, and press Select.
b. Push Select until “Number of Boards:” appears and rotate Select until the
desired the number of boards shows “4”. Press Select. Note: use “3” for
BMS-36, “4” for BMS-48, and “5” for BMS-60
c. Push Select until “Cells in Board 1:” appears and turn Select until the
actual number of connected cells in the first board is shown and press
Select. Continue entering cells in boards 2, 3 and 4.
d. Pressing Select until the Config menu appears, then select “Back” to get
to the Main Menu.
2. Configure Battery Monitoring Voltage Thresholds. The BMS has adjustable
thresholds for battery monitoring. These thresholds can be adjusted to
accommodate different battery chemistries, or to suit user needs. Consult your
battery manufacturer for specific recommendations. Typical Thresholds are
shown in Table 1. Balance voltage setting should be .1v below the battery High
voltage cutoff voltage.
Table 1: BMS Threshold Settings for Lithium Battery Chemistries.
LiFeP04
(3.2v)
Over V: High
Voltage Cutoff
Under V: Low
Voltage Cutoff
Bal V: Balance
Voltage
Hysteresis
Voltage
Li-Cobalt
(3.6v)
Li
Manganese
(3.7v)
Ni-CoManganese
(3.2v)
3.912v
4.20v
4.20v
4.104v
2.496v
2.496
2.496
2.496
3.864v
4.104v
4.104v
4.008v
0.0465
0.0465
0.0465
0.0465
From the main menu select:
SETUP->CONFIG.
a. Low Voltage Cutoff: Push Select until “Under Voltage:” appears. Turn
Select until the desired voltage is shown and press Select.
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b. High Voltage Cutoff: Push Select until “Over Voltage:” appears. Turn
Select until the desired voltage is shown and press Select.
c. Balance Voltage: Push Select until “Balance Voltage:” appears. Turn
Select until the desired voltage is shown and press Select.
d. Push Select until “Temp limit:” appears, set the maximum temperature
(35 degrees C is recommended) and press Select
Continue pressing select until the Config menu appears, then select “Back” to
get to the main menu.
Restart the BMS: from the main menu, Select “Restart” and press Select.
3.1 Current Monitor Option
If the current monitor option is installed, the current monitor needs to be configured.
The current monitor displays instantaneous current usage in run mode, and track KWh
power used by the battery system. The power tracking data is collected every 1 second,
and is either counted UP for total used or counted down from the current monitor limit.
The configuration and limits are set from the configuration menu.
From the main menu select:
SETUP->CONFIG.
Select Current monitor: Yes
Current Monitor Count Up: Yes.
Current Monitor Limit: 13 KWH
During initial installation, suggest is to count up and set the limit to well above the
expected battery capacity. Once the battery system has been cycled, the upper limit of
power battery power as measured from the current monitor will be known. This limit can
be set into the configuration for a count-down available battery power. Power calculation
is done as measured Pack Voltage * measured Current usage, measured each second.
Pukerts effect are not factored into the battery power usage.
Remaining or used power is displayed on line 2 of the display in run mode. Power
usage is reset on system startup, or when any balancer is activated
4 Flex BMS Operations
This section covers the basic operations of the BMS. The complete software menu
hierarchy is listed in Appendix B. There are two operations modes, Monitor for day-today operations of the BMS, and Balance, for running charging/balancing cycles to
balance the battery pack.
4.1 BMS Monitor
To start the BMS monitor. From the main menu, turn Select to “Run” and press Select.
The BMS will enter the monitoring mode. To exit the monitor mode, press and hold the
select button as described in the Administration section.
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In the monitor mode, the BMS monitor display has two lines. The top line will indicate
the Monitoring State, the current pack voltage and highest temperature.
The monitoring states are:
 OK: this state indicates that all cell voltages and temperatures are within set
tolerance. The BMS system does not detect significant change in pack voltage
indicating charge or discharge.
 BAL+: This state indicates that one or more cells is above the balance threshold and
the balancer load in enabled for a cell. The charger is on.
 BAL-: This state indicates that one or more cells is above the balance threshold and
the balancer load in enabled for a cell. This charger is off. This mode is only used in
balance mode.
 END : End of charge cycle. When a single cell reaches the cut-off threshold, the
charger is cut-off, balancer loads disabled. The BMS will stay in this state until the
select button is pressed.
 TEMP!: This state indicates that a temperature threshold has been exceeded.
Charge is cutoff, balancers are cutoff, and the fan is on. An Alert is displayed.
In monitor mode, the Console may display Alerts by flashing the backlight. (Audible alert
is in next version). An Alert is cleared by pressing the “Select” for one second.
Alerts may occur for many reasons, including:



Over Temperature
Low Battery Threshold
System Error
The bottom line on the monitor rotates thru several messages:
Min X.XXXv nn
This identifies the Minimum cell voltage on cell nn, with
voltage x.xxx volts
Max X.XXXv nn
This identifies the Maximum cell voltage on cell nn, with
voltage x.xxx volts
Bal Cells n
When cell balancers are active, this indicates the number of
cells balancers enabled.
P xx.xx KWh left
If current monitoring enabled in count down mode this
indicates the calculated power left in the battery pack
P xx.xx KWh used
If current monitoring enabled in count up mode this
indicates the calculated power used.
Any system errors are listed in the bottom line of the display. The bottom line can be
read as:
Severity Code [Board ID-Cell ID]
Severity is either LOG for a simple log report, WARN indicating a Warning condition, and
ERR indicating a serious error or fault. Codes are listed in the Appendix A. Board ID
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and Cell ID are the Board number [0 to 7] and cell on the board [0-11] that reported the
fault.
The BMS continues to operate in the Monitor mode indefinitely. To exit the monitor
mode, hold down the select button as described in the Administration section.
During charging in monitor mode, a charge cycle will near completion using balancing,
and after one cell has passed the over voltage threshold, the charger will be cutoff,
balancers turned off, The BMS will be in the ‘END’ state. To re-enable the charger,
press the select button.
4.2 BMS Balance
The BMS can be run in a Balance Mode to cycle thru up to 20 charger or balance cycles
to balance the Li batteries. The Balance cycle should be used whenever battery any
battery is replaced or one of the batteries is consistently low. Balancing will help bring
the lower voltage batteries up to the same level as the rest of the pack.
To start the BMS Balance mode, exit the monitor mode by holding down the select
button as described in the administration section. From the main menu, select BAL.
Then select the number of balance cycles [1-20]. Generally, 4-5 balance cycles should
balance most lithium battery packs.
In this mode, the charger will activate, and the balancers will trigger upon balance
voltage. When a battery reaches the high voltage cut-off, the charger will be cut-off, and
the balancers will stay enabled until all are below the balance voltage, then the charger
will be re-enabled. This will cycle the specified number of cycles.
The balance and charge cycles will stop when all balancers are activated.
The balance function will keep batteries in balance. New batteries may come from the
factory in charged or discharged state. New batteries that have significantly difference
state of charge may need to be manually balanced or individually charged.
5 Administration
To administer and configure the BMS, the BMS must be out of the monitor mode. To
exit the monitor mode, press and hold the Select knob for at least 15 seconds, until
the display changes. This will bring up the Main Menu.
The Log Function:
A log function is provided to keep the latest 50 log entries in the BMS. To view the log
entries, the system must be out of the monitor mode.
To administer the Log, from the main menu, select “Setup”, then select “Log”. This
brings up the Log Menu.
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To view the Log, select “ViewLog”. Turn the Select knob to the right for later entries,
turn to the left for earlier entries. Entry format is the same as Line 2 of the monitor
mode. Time is included on the second line to indicate the relative number of seconds
since the system was restarted. Log codes are found in Appendix A. Press Select to
exist the log viewing mode.
To reset the Log, select “ClearLog”.
For more information contact
Mark Hardy, Hardy EV LLC
Hardy.mark@convertthefuture.com
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Appendix A
Log Codes and Explanation
Logged errors and warnings may be displayed during system startup, during any read
operation or during monitoring. Log information is useful for diagnosing problems with
the system. Codes are displayed as a CODE followed by a [board-cell] indicator.
Codes are listed in the appendix. Board and Cell are the Board number [0 to 7] and cell
on the board [0-11] that reported the fault.
Table A-3 Log Codes
Meaning
Value
(decimal)
1
Title
3
UNDER_VOLTAGE_CELL
5
CELL_ERROR
7
8
9
11
MONITOR_START
MONITOR_STOP
POWER_ON
OVER_TEMPERATURE
12
13
14
SELF_TEST_FAIL
PEC_ERROR
ACK_WARNING
15
OPEN_WIRE_ERROR
16
LOAD_FAILURE
17
NO_CELL_READING
20
21
22
CHARGE_START
CHARGE_STOP
POLL_ERROR
23
TEMP_OK
25
EXT_POWER_OFF
OVER_VOLTAGE_CELL
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An individual cell recorded overvoltage
An individual cell recorded undervoltage
A cell’s value were out of range.
Wiring for the cell may be faulty, or
the cell balancer may be damaged.
Monitor program started.
Monitor program stopped
BMS started
Sensor recorded over –
Temperature
Initialization self test failed.
Communications PEC error
Operator presses Select to
acknowledge and clear alert..
Balancer check failure, check
system wiring.
Balancer check failure, check
system wiring
No cell voltage found, check config
system wiring.
Charger was turned off
Charger relay was turned off
Board polling time was out of
parameters
Temperature reduced to to below
high threshold
External Power Switch turned off.
BMS 0.6d
Installation and Operations Guide
Appendix B
Software Menus
Main Menu
Run:
Bal:
Read:
Config:
Restrt:
Starts the monitoring program
Starts the balancing program
Reads and displays current cell voltages for each cell
Configuration Menu
Restarts the BMS
Configuration Menu
Setup:
Sets configuration parameters
Over V:
Sets the cell over voltage threshold
Under V:
Sets the cell under voltage threshold
Bal V:
Sets the cell balance voltage threshold [3.8
Max Temp:
Sets the system maximum temperature (celcus) [45]
Boards [1-8]:
Sets the number of boards in the BMS system
Cells on Board n [4-12]: Sets the number of cells on each board
Hysteresis:
Sets the hysteresis voltage for balance turn off. [0.04]
Current Monitor:
Yes/No whether the current monitor is installed.
Current Count Up: Yes/No sets whether KWh are counted up or down
Max KWatt-Hrs:
Sets the number of KWh for count down.
Tst:
Test Menu
Log:
Log Menu
Light:
Turns on the backlight
Back:
Returns to Main Menu
Log Menu
ViewLog: Displays all the log entries
Clear:
Deletes all log entries
Back:
Returns to Main Menu
Test Menu
CelTst:
ComTst:
AmpTst:
Back:
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Runs Diagnostics on each cell, check balancers
Runs Diagnostics on the interboard communications
Runs test program for the current monitor
Returns to Main Menu
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Installation and Operations Guide
Appendix C
Data Logging and Formats
If the USB Data Logging option is provided with the BMS, the BMS will detect the
presence of a USB stick in the BMS. If the USB memory stick is not detected at startup,
USB recording will be disabled. The BMS can be restarted using the ‘Restrt’ option
from the main menu.
The USB Data Logging option uses internal USB stick to log cell voltage, balance
information and alerts every minute. Logs errors as they occur. Data is recorded on a
USB stick inside the BMS Box. Data is in comma separated variable (csv) format that
can be read and analyzed using a spreadsheet program such as Excel.
Data logging starts when the BMS is restarted. A file is created or opened called
‘BMSLOG.TXT’ Each row of data is in ASCII format, and ends with a carriage return and
line feed.{CR-LF}.
After restart the first line of data recorded is “Start BMS Log {CR-LF}”.
The next line of data recorded is the header information to help identify each data
element when imported into in a spreadsheet. The length of the header depends on the
number of cells configured. The example below show a system configured for 12 cells
on one board:
Time (s), Pack_Voltage (v), Max_temp (c), Monitor_state,cell 1[0-0], cell
2[0-1], cell 3[0-2], cell 4[0-3], cell 5[0-4], cell 6[0-5], cell 7[0-6], cell
8[0-7], cell 9[0-8], cell 10[0-9], cell 11[0-10], cell 12[0-11], Balance 0-7
(hex), Last Log {CR-LF}
Each of these data elements are explained in the data logging formats in Table C-1
Log Data Element
Time (s),
Pack_Voltage (v),
Max_temp (c),
Monitor_state,
cell 1[0-0],
cell 2[0-1],
cell 3[0-2],
…
Balance 0-7 (hex),
Last Log
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Table C-1. Data Logging Format
Value
Decimal number of seconds since the BMS was
restarted.
Total pack voltage, in Volts
Maximum temperature of all active probes, in degrees
celcius
State of the monitor, see table C-2
Cell Voltage for board id 0, cell id 0, in Volts
Cell Voltage for board id 0, cell id 1, in Volts
Cell Voltage for board id 0, cell id 2, in Volts
Hex code identifying the balancers that are active. Bit 1
is cell id 0.
Log entries are given with a severity level (Log, Warn,
Error), a code number (See Table A-1), followed by the
board and cell number.
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Installation and Operations Guide
Monitor State Code
10
12
15
17
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Table C-2 Monitor State Codes
Meaning
Monitor Mode, charge enabled
Balance Mode, at least on balancer is enabled
Over Temperature mode, balancers and charger
disabled
End of Charge state, charger disabled.
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