Cell Management Module (CMM)

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Merry Farmer
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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

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

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

1 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. June,

2 By default the temperature measured and reported is the temperature inside the CMM itself. As the CMM is connected using short lengths of 2.5mm 2 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 undervoltage. 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 (2008) / SANS (2009) IEC (2010) / SANS (2008) June,

3 Electrical Specifications Operating cell voltage range Valid cell voltage readings region Maximum overvoltage Reverse polarity cell voltage (2V CMM) Reverse polarity cell voltage (4V CMM) 0.65V to 6V 30V -2.5V -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 , IEC Environmental IP67A, IK05 June,

4 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 overtemperature 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 overtemperature 0.85V 50 C BLUE LED Flashing pattern 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. Condition 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. June,

5 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 Always on, but brightness is proportional to the duty cycle of balancing resistor. Brighter indicates higher balancing current. Condition 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. 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. 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. June,

6 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 A June,

7 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. Current 0,8mA 0,7mA 0,6mA 0,5mA 0,4mA 0,3mA 0,2mA 0,1mA CMM average current and power consumption vs cell voltage 1,6mW 1,4mW 1,2mW 1,0mW 0,8mW 0,6mW 0,4mW 0,2mW Power 0,0mA 0,0mW 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 Current Power Cell Voltage June,

8 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. June,

9 Mechanical Layout Dimensions in (mm) Alternative connection lugs and wiring lengths are available in OEM quantities June,

Monoblock Management Module (MMM)

Monoblock Management Module (MMM) 6V MMM and 12V MMM versions Monitoring every 2 seconds of monoblock voltage & temperature 3W of passive balancing configurable for desired float Amount of balancing coulombs