Cell Management Module (CMM)docs.balancell.com/CMM_data_sheet.pdf · polarity connection • Measures directly across cell terminals to avoid voltage drops due to cell interconnects

June, 2016 1 www.balancell.com

Cell Management Module (CMM) ________________________________________________________________________________________

2V CMM and 4V CMM versions

• Monitoring every 2 seconds of cell voltage & temperature

• 3W of passive balancing configurable for any cell

chemistry

• Amount of balancing coulombs recorded and reported

• Operating range from 0.6V to 6V, (both 2V and 4V

versions)

• Tolerant of an overvoltage up to 30V and to reverse

polarity connection

• Measures directly across cell terminals to avoid voltage

drops due to cell interconnects

• Makes a virtual four-terminal measurement by drawing

negligible current during the actual measurement instant.

• Oscilloscope mode facilitates cell impedance analysis

• Works on any chemistry and pack up to 128 cells

• LED indicators for balancing, warnings and status

• Communications over a single signal wire that is fully

isolated

• High noise immunity communication using RF Modulated

signalling

• Low power as typically uses less than 0.2mA at 2V

(<0.5mW)

• Autonomous operation in a stand-alone configuration

• External thermistor option for temperature measurement

• Fully over-molded, insulated, shockproof (IK05), waterproof (IP67A) and sulphuric acid proof.

Description

The Cell Management Module (CMM) is a per-cell

device, with one CMM connected to each cell of

a battery pack. Used in conjunction with a single

Battery Energy Meter (BEM), a complete Battery

Management System (BMS) can be implemented.

The BEM acts as a central management unit to

collect information from the individual CMMs

and distribute commands to them. The CMM is

designed to operate on any cell within a voltage

range of 0.6V to 6V. Two versions with different

balancing resistor values are available being a 2V

version (1-3V cells) and a 4V version (3-5V cells).

The two versions only have different balancing

resistors. The CMM performs three main

functions: continuous monitoring of cell voltage

and temperature, measuring and reporting cell

voltage, temperature and balancing current and

passive balancing of a cell. The CMM is designed

to be used in any pack configuration with any

number of cells in series from 2 to 128, and bigger

banks can have a split BMS’s sections.

The CMM requires only two terminals for voltage

measurement instead of the usual four as no

current is drawn during the instant when the

actual cell voltage measurement is being done.

It can capture and report an oscillogram waveform,

with a 1k sample length at a variable sample rate

from 20sps to 96ksps. This is carried out

synchronously with all the CMM’s throughout the

pack, together with the BEM, which captures the

battery pack voltage and current. This allows

detailed cell impedance analysis to be performed

using anything from a DC step, to the 50/60 Hz

ripple from the charger, to a 1 kHz injected signal.


By default the temperature measured and

reported is the temperature inside the CMM itself.

As the CMM is connected using short lengths of

2.5mm2 wire directly to the cell terminals, this

internal temperature is normally a fair indication of

actual cell temperature. An optional external

thermistor can be factory fitted to the CMM if

required, and would then be reported additionally.

The CMM provides up to 3W of passive balancing

on any chemistry. The voltage set-points at which

passive balancing occur can be fully configured.

This function can also be enabled or disabled as

required.

The module is fully over-molded and made to meet

the very harshest environmental conditions, being

completely insulated, mechanically robust, flame

retardant, waterproof and acid proof. It can

survive complete submersion in concentrated

sulphuric acid. This allows its use in most

environments including flooded lead acid cells in

motive applications.

The communication between a CMM and BEM is

carried out over a fully isolated (1500V) and

floating single wire. An RF modulated signal is sent

over this wire using a proprietary communication

protocol with multiple levels of redundancy and

error checking. This was designed to deal with the

high levels of electrical noise present on large cells

in motive applications. Large cells (>200Ah) will

have low impedances, however, the cell to cell

interconnects and physical battery layout add

inductance to the battery pack. Hence noisy

industrial equipment with very high current

transients will cause the battery terminal voltage

to exhibit significant transient voltage spikes. This

necessitated the use of an RF modulated protocol

by the CMM so that it can communicate through

the noise in these environments.

The CMM offers continuous monitoring,

performed every 2 seconds, for limit conditions on

both cell voltage and temperature. These limit

conditions are fully configurable and if exceeded

are reported to the BEM as well as being visibly

indicated on the CMM via the on-board LEDs. This

enables immediate visual identification of any cell

at fault. The three limits that are user configurable

are over-temperature, over-voltage and under-

voltage.

The CMM module in monitoring mode consumes

very little power, since it is in sleep much of the

time between the one minute reporting and two

second monitoring operations. The power and

current requirements are given in the typical

performance curves section (e.g. 0.2mA on a 2V

cell). If cell voltage is below 0.6V then the CMM

shuts down, where it draws less than 0.1µA.

The CMMs also offer a failsafe feature, as they

continue to operate in a stand-alone manner even

if the BEM fails. In this case the balancing of the

pack continues to be performed and the LEDs

illuminate when limits are exceeded allowing

visual identification of cells at fault. Putting an

intelligent CMM on each cell creates a more

resilient battery bank made up of “smart cells”.

The distributed nature of implementing a module

per-cell means that failure of individual CMM’s will

not interfere with the operation of the rest of the

system, making the BMS more robust.

Replacement of a single CMM is an easy and cost

effective fix, compared to the replacement or

repair of an entire BMS. The complete isolation of

each module also means that the battery stack can

be broken or disconnected to replace cells with no

damaging effects on the rest of the BMS.

The CMMs have meet the CE pre-compliance tests

for electrostatic discharge, radiated emissions and

radiated susceptibility.

• CISPR22 (2008) / SANS 222 (2009)

• IEC 61000-4-2 (2008) / SANS 61000-4-2 (2009)

• IEC 61000-4-3 (2010) / SANS 61000-4-3 (2008)


Electrical Specifications

Operating cell voltage range

Valid cell voltage readings region 0.65V to 6V

Maximum overvoltage 30V

Reverse polarity cell voltage (2V CMM) -2.5V

Reverse polarity cell voltage (4V CMM) -4.5V

Operating temperature range

Operating temperature range -25°C to 80°C

Default cell over temperature warning 50°C

Balancing

Balancing Power Maximum (2V And 4V CMM) 3W

Balancing resistor (2V CMM) 2.2Ω

Balancing resistor (4V CMM) 6.8Ω

Balancing stops When cell voltage >6V

Balancing stops When CMM temp >85°C

Balancing resumes When CMM temp <70°C

Relative cell voltage measurement (CMM to CMM) Typically at 30°C, Max range -25°C to 80°C

Measurement time < 200us

Measurement synchronization between all cells < 200us

12 Bit ADC, Quantization of ADC 1.5mV/bit

Relative measurement accuracy Typ = +/-3mV Max = +/- 9mV

Absolute cell voltage measurement accuracy Typically at 30°C, Max range -25°C to 80°C

Cell voltage from 0.6V to 6V Typ = +/-6mV Max = +/- 12mV

Oscilloscope cell voltage measurement Typically at 30°C, Max range -25°C to 80°C

Sample memory, 12 bit, same range as above 1000 samples

Measurement synchronization between all cells < 4us

Sample rate 20sps to 96ksps

Total sample period (of whole oscillogram) 10ms to 50 seconds

Temperature Measurement

Reported 8 bit value range (Internal, Chip level:) -128°C to 127°C

Accuracy Typ = +/- 1°C Max = +/- 3°C

External, 10k thermistor:

12 Bit ADC, quantization of ADC TBD – implementation specific

Total accuracy TBD – implementation specific

Certifications

CE (pre-compliance) CISPR 22, IEC 61000-4-3, IEC 61000-4-2

Environmental IP67A, IK05


Operation

Limits: Over voltage, over temperature and under voltage limits can be set on CMM’s. The flashing pattern

is given in the table below. The cell temperature is based on the CMM’s estimate via its connection leads.

The estimate of cell temperature is adjusted to compensate for any balancing heat generated by the CMM.

RED LED

Flashing pattern Condition Default

50ms on / 450ms off = Short pulse twice a second

Over-temperature 50°C

450ms on / 50ms off = Long pulse twice a second

Over-voltage 5.5V

Fully on

Over-voltage and over-

temperature

5.5V

50°C

50ms on / 3000ms off = Short pulse once every 3

seconds

Under-voltage 0.85V

50ms on/ 200ms off/ 50ms on / 3000ms off = two short

pulses once every 3 seconds

Under-voltage and over-

temperature

0.85V

50°C

BLUE LED

Flashing pattern Condition

On power up, the BLUE LED will come on once only for 3 seconds.

NOTE: This is used to show correct polarity connection. Its absence

indicates that the device has been connected incorrectly.

Correct Initial connection

50ms on/ 200ms off/ 50ms on/ 200ms off/ 50ms on/3000ms off

= three short pulses once every 3 seconds

Un-configured

50ms on/ 200ms off/ 50ms on/ 200ms off/ 50ms on/30000ms off

= three short pulses once every 30 seconds

Lost communication

Whenever a message for itself is received correctly, the CMM will

flash its BLUE LED once for 50ms = short pulse.

Received Message Correctly

Note on un-configured state: If the CMM has not been configured it will flash its BLUE LED for three short

pulses, every three seconds. This is to indicate that a CMM has not yet been addressed by the BEM.


Note on lost communication: If the CMM has not received any communications from the BEM to itself for

more than 90 seconds it will flash its BLUE LED for three short pulses, once every 30 seconds. This is used to

indicate either a bad communication connection to the CMM itself, or that the BEM has stopped

communicating.

YELLOW LED

Flashing Pattern Condition

Always on, but brightness is proportional to the duty cycle of

balancing resistor. Brighter indicates higher balancing current.

Balancing

Reverse Polarity Connection

The CMM can handle a reverse polarity connection

provided it is within the nominal cell voltage

region. This is -1 to -3V for a 2V CMM and -3 to -5V

for a 4V CMM.

Passive balancing

Passive balancing is also called dissipative or

resistive balancing and is carried out by drawing

some current/charge/energy off a cell and

dissipating it as heat in a resistor. Passive balancing

is only able to sink current from a cell, which is a

negative cell current and reported as such.

The CMM can perform up to 3W of passive

balancing. This function can be enabled or

disabled, and a variety of algorithm approaches

can be used. These approaches include a simple

on/off balancing around a single level, to

proportional, to proportional integral, to scaling all

balancers according to highest cell, or maximum

temperature etc.

VRIP balancing algorithm

The default algorithm used by the CMM's is termed

the VRIP algorithm and this is an acronym for

Constant Voltage, V, Constant Resistance, R,

Constant Current, I, Constant Power, P = VRIP.

The CMM is set with a balancing level and a

maximum balancing level from the configuration

tool. The maximum balancing level must be in the

region of 10-20% higher than the balancing level.

When a Cell reaches the balancing level the CMM

will then start to perform integral control of the

balancing current to keep cell voltage constant. In

other words, the balancing current will be adjusted

up or down to keep the cell voltage at exactly the

balancing level. If a charger is set correctly then at

top of charge the current will be reduced to

something that will not over power the balancing.

If this is the case then, as a cell reaches the

balancing level, the balancing current will

progressively increase, and hence the cells will

receive progressively less charge current until it

has truly reached the balance level.

The second region is constant resistance which

appears as a pure resistance connected

permanently across a cell, and as cell voltage

increases the current increases. The third region is

the constant current region, meaning a constant

current is drawn from the cell as voltage increases

further. However in practice this region does have

a small positive slope, so higher voltages will draw

slightly higher current. Thus if the charger current

is too high, then the cells will go into the constant

resistance or constant current region, but the

system will still have a balancing effect as higher

cells will have more balancing current drawn off

them. To explain it in converse, if this was not the

case and higher cell voltages drew less current

once they are over the balancing level, they are

then in danger of going even higher than the other

cells and the system becomes unstable.


Provided the cell voltages never exceed the

maximum balancing level, the system will remain

stable as higher cell voltages will always have more

current being drawn off them. The maximum

balancing level is the point where maximum cell

balancing current and power will occur. It is the

point that the cell voltage should never exceed. If

the cell voltage goes even higher than the

maximum balancing level and goes into the fourth

region of constant power dissipation. In this region

the CMM will go into a constant power mode to

prevent itself from overheating, and current will

decrease with increasing voltages. This is simply a

protection mechanism and in theory the cell

voltage should never be in this region. However,

even if it does end up in this region, the design

philosophy is that the CMM should and will

continue to draw power from the cell in an effort

to bring its voltage down again.

More balancing examples can be found by

downloading spreadsheet from website. Table

below illustrates levels for 2V lead acid cell.

Resistor 2.2 ohms

Maximum Power 3 watts

Balancing level 2.25 V

Max balancing level 20%

Max balancing level 2.7 V

Maximum current 1.111111111 A


Typical Current and Power consumption - of CMM during normal operation, assuming no LEDs are on,

and no balancing. Any more activity from CMM, e.g. readings more often, will increase power slightly.

0,0mW

0,2mW

0,4mW

0,6mW

0,8mW

1,0mW

1,2mW

1,4mW

1,6mW

0,0mA

0,1mA

0,2mA

0,3mA

0,4mA

0,5mA

0,6mA

0,7mA

0,8mA

0,0V 0,5V 1,0V 1,5V 2,0V 2,5V 3,0V 3,5V 4,0V 4,5V 5,0V 5,5V 6,0V

Po

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Cu

rre

nt

Cell Voltage

CMM average current and power consumption vs cell voltage

Current Power


CMM Installation

The CMM connects to a flooded lead

acid cell in a completely insulated,

waterproof and acid-proof manner.

The standard over-molded M10 x

22mm bolts are replaced with a similar

M10 x 22mm bolt that includes a

power take off on top with a M5

thread. An over-molded M5 x 8mm

bolt is used to make and seal the

connection to the bolt head. The

domed-ring on either side of the CMM

over-molded lug will seal with the M10

bolt plastic surface below and the M5 plastic surface above. In addition, a very good electrical connection is

made directly with the bolt head, which is a very low resistance path to the cell as it is bolted directly into the

cell terminal. This provides the best electrical path for measurement and balancing of the cell, and provides

a good thermal connection between the CMM and cell. This gives a good representation cell temperature and

is good for dissipating heat when balancing. The figure shows CMMs installed on a pack with Balancell power

take-off bolts.

Communications wire Installation

Communication is done using a single wire that is fully capacitively isolated at all connection points and hence

is capable of floating at any DC voltage level. It uses the actual battery pack as a return path. Hence to minimise

noise and pick up interference the communications wire and the cell and cell interconnects should make a

“twisted pair”, or the area between them should be minimised. Please see communications wire installation

guide and video.

2V CMM and 4V CMM

These are identical except for their balancing resistor values. They can be identified on the underside of the

CMM by an arrow pointing towards the numbers 2 or 4, as shown below.


Mechanical Layout

Dimensions in (mm)

Alternative connection lugs and wiring lengths are available in OEM quantities

Documents

Cell Management Module (CMM)docs.balancell.com/CMM_data_sheet.pdf · polarity connection • Measures directly across cell terminals to avoid voltage drops due to cell interconnects