Cell Management Module (CMM)docs.balancell.com/CMM_data_sheet.pdf · polarity connection •...
Transcript of Cell Management Module (CMM)docs.balancell.com/CMM_data_sheet.pdf · polarity connection •...
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.
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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)
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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
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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.
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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.
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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
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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
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Cell Voltage
CMM average current and power consumption vs cell voltage
Current Power
June, 2016 8 www.balancell.com
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.
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Mechanical Layout
Dimensions in (mm)
Alternative connection lugs and wiring lengths are available in OEM quantities