AP9920X Battery Management System APC Global Services Dan Lambert, Technical LiaisonAEG Design Team

AGENDASafetyDocumentationBattery Management System (BMS Theory of Operation)LabBattery Management System (BMS Installation)Battery Management System (BMS Software)Technical Scope of WorkSummary

SAFETYStorage batteries present various hazards to personnel who are required to install and maintain them. The primary hazards are:Sulfuric AcidElectric ShockExplosive GasesNever work on a battery system aloneNo food or drink in the presence of flooded batteriesAppropriate personal protective equipment must be usedEgress from the battery room must be kept clear at all timesNever attempt to move batteries without the proper equipment

SAFETYSulfuric Acid Burn SafetyLead Acid type Storage Batteries contain concentrations of sulfuric acid (electrolyte) that can cause severe burnsWhen handling electrolyte, face shields, chemical goggles, rubber aprons and rubber gloves must be wornIn the event that sulfuric acid comes in contact with skin, immediately flush thoroughly with water. Do not use baking soda solutions directly on skin. Get medical attention immediatelyIf Sulfuric acid comes in contact with the eyes, flush with water for at least 15 minutes and get medical attention immediatelyIf Sulfuric acid is ingested get medical attention immediatelySpilled electrolyte should be neutralized with a solution of one pound of baking soda per one gallon of water

SAFETYElectrical Shock and Burns:

Batteries may contain large amounts of stored electrical energy. Due to the nature of batteries the source cannot be completely isolated or tagged out. Electrical shock and burns can result from coming in contact with battery terminals or from short circuits from metal toolsAlways use insulated toolsWhen working with batteries, properly insulated tools MUST be usedGloves must be worn when handling batteries or making connectionsAll metal jewelry must be removed Never place tools or metallic objects on batteries One person at a time in a battery cabinet or rack

SAFETYElectrical shock and burnsWhen working on batteries, the charging source and all parallel strings must be disconnectedWhen working on a grounded battery string, always disconnect the ground cable first and reconnect the ground cable lastWhen removing/replacing cells, open the string in several places to reduce the voltage potential, preferably to 48 VDC or lessWhen cables are removed from one terminal while remaining attached to another terminal, the cable lugs must be insulated completely with electrical tape or appropriate insulating material

SAFETYValve Regulated Lead Acid

A cell that is closed under normal conditions by a non-return (control) valve that allows the escape of gas if the internal pressure exceeds a predetermined value. The valve shall not allow gas or air to enter the cell. The maximum pressure reached inside the cell under any circumstances can be requested from the manufacturer.

The cell cannot receive additions to the electrolyte (topping up).

DOCUMENTATIONUser ManualInstallation ManualBattery Management System Retrofit KitProduct SpecificationTechnical Scope of Work

Battery Management SystemTheory of Operation:

APCs Battery Management products are the standard for operations which rely on an uninterrupted and reliable supply of battery power.

Our Unique Technology combines battery monitoring and testing with Automated-Single-Cell-Charging (ASCC) for true Battery Management.

Batteries are like people

Batteries are like peopleElectrochemical energy machinesLatent defects (inherited, congenital)Subject to abuse, stress & diseaseHave individual needs & characteristicsHave individual rates of deteriorationDont always work well togetherHave a physical death (sooner or later)

Sealed Battery ReliabilityA Study of 25,000 Sealed Batteries Indicated that After Two Years They Could Not be Considered ReliableSource: D.O. Feder, PhD, Electrochemical Energy Systems, Inc.

VRLA Failure HistorySource: D.O. Feder, PhD, Electrochemical Energy Systems, Inc.

Battery Reliability & Life FactorsLatent Defects Number of dischargesDepth of each dischargeOperating TemperatureCharge time (continuous or intermittent)Charge voltage (polarization)Charge accuracy (high or low)

Battery Failure ModesShorted CellsOpen CellsSulfationWeld FracturesCorrosion Internal & ExternalDry outPlate Warp/Separator CompressionRuptures & LeaksThermal RunawayWear out

Normal Battery Life

We Can Prevent These Latent Defects--->We can detect and alarm on theseSource: BCI, 107th Convention

Thermal Runaway

Cell Circuit

Rp-Rp+ ReCpRxc-Rxc+ Charge Connection- PlateElectrolyte +Plate+Connection Age Sulfation Compression Dry outAcid ConcentrationTemperatureImpuritiesCorrosionTorqueSurfaces

Newer cells have lower resistance Forces older cell voltage too highNewer cell voltage is too lowTraditional Equalization IneffectiveIndividual Cell Charging Integrates the new with the oldCell Replacement is now successful Mixing New & Old Cells

Charging Multiple Cells CAPACITY LIFE & WATER LOSS LOSS

Individual Recharge vs Time Time >VOLTS

Why Automate?Increased Battery LifeImproved Battery IntegrityReduced Operating CostsProactive Maintenance Accurate & Complete RecordsFull Time Battery Status

APCs ApproachWork Continuously-Monitor/Test/CompareIndicate if voltage is outside limitsCorrect undercharged cellsSave measured data and discharge eventsTest each cell with charge currentRecognize problemsInform user of availability during discharge

Modes of OperationSystem Self-test/Calibration-ContinuousCell/Jar Voltage Scanning- ContinuousCell/Jar Voltage Equalization- ContinuousTemperature Measurement-ContinuousResistance Stability Test - ScheduledCharge State Stability Test ScheduledTemperature Stability Test

Alarms Alarm conditions cover: Individual Battery VoltageOverall String Voltage Ambient & Pilot TemperatureIndividual Resistance State of Charge Individual Temperature System Self-test & CalibrationKnee Detection

Knee Detection Knee

Isolated ChargerCell/JarSelectorsVoltageMonitorCurrentMonitorCPUManagement System Block Diagram264 CellsCom/Display 1234

CPUManagement System Block Diagram1234The CPU executes the firmware instructions and selects individual batteries, closes the boost and alarm relays, operates the analog to digital converters and communications ports.The CPU compares the actual measured values with the alarm set points and the previously learned benchmark data.

Isolated ChargerManagement System Block Diagram1234The isolated charger is a transformer isolated DC supply that is set to a higher voltage than found on an individual battery.When the output is connected to one of the individual batteries, current will flow from the isolated charger into the selected battery.Since there is no reference to the other batteries, all of the current is directed into only the one selected.

CurrentMonitorManagement System Block Diagram1234The current monitor senses the amount of current that is accepted by the individual battery from the boost supply.The voltage drop across a 1 ohm resistor that is in series with the output of the boost supply is proportional to the amount of current delivered.The proportional voltage signal is sent to the processor for comparison with earlier current measurements of the same individual battery.Differences in current indicate instability in temperature, charge state or circuit resistance.

VoltageMonitorManagement System Block Diagram1234The voltage monitor converts the analog battery voltage signal to a digital format.The digital output is sent to the processor for comparison against the voltage alarm limits and evaluation of the individual battery deviation in actual voltage compared to the ideal average voltage.

Cell/JarSelectorsManagement System Block Diagram264 Cells1234The cell/jar selector uses relay contacts to connect the battery management system to one of the batteries. When the associated relay is pulled in, the system can monitor the voltage or route charge current to that individual battery.The selector is like a multi-plexer with multiple inputs and only one output.

Experiment: Float vs Individual Charge New VRLA Cells, Same Lot24 Float Charged & 24 ASCCSame Environment16 DischargesEquivalent of 8 Years-January 2000Teardowns in April 99 & January 2000Conducted by Battery Technology Center

4203500APCFloatAmp-HoursCharge Energy Comparison88% Wasted Energy& 2.5 X Deterioration

Individual Recharge Energy

Grid Corrosion Depth

Float = > .5 mmAPC = < .2 mm.5/.2 = 2.5 x Less

Float Charged Cells vs Individual 2.5 x Grid Growth at 8 Years Grown > 3/16Grown < 1/16

Float Charged Plates at 8 Years Soft Active Material & Severe Spalling 5/16 Warping

APC Hard Active Material with Minimal Spalling & Warping< 1/16 Warping

Discharge APC at 10 Years 16th Discharge at 1 Hour Rate Float 0 of 24 Cells APC 22 of 24 CellsAll 24 Float Cells Are Below 80% Capacity at 10 Years

Features & Benefits

Individual Cell/Jar ChargingA Charger for Every Cell/JarPermits Individual ReplacementsIncreases Battery LifeFull Time Equalization Prevents Thermal Runaway

Features & BenefitsActive Current TestingTracks Electrochemical StabilityCell/Jar & Connection ResistanceCell/Jar State of ChargeInternal Cell/Jar TemperatureAutomatic Trending of ResultsEarly Identification of ProblemsKnee Detection backup

Features & BenefitsRemote AccessWeb Browser, Telnet, & FTP via TCP/IP over EthernetRS232 or RS485 Serial (ModBus via RS-485)Alarm Control/AnalysisAutomatic TrendingComputer Crunches DataNo External Computer RequiredEarly Warning of Problems

Features & BenefitsSelf Contained SystemSolid State DiskStores HistoryStores DataExternal Computer Unnecessary

Automatic TrendingLearns initial resistanceCompares values with file valuesAlarms if < or > Set point

SummaryBattery Reliability & Life is a ProblemAPC Improves Battery Reliability & LifeVoltage, Current & Resistance are EssentialTest Current Reveals the Electrochemical StatusMonitoring & Individual Charging=ManagementLow Cost of OwnershipIncreased Battery Life Decreased Operating Costs

BMS InstallationBMS ConfigurationStandard PracticesCabinet Accessibility / PreparationDIP Switch ConfigurationCabinet Door ReplacementMounting the BMSSoftware Details

Batteries are very similar to people in that a variety of internal and external factors control their performance and the length of their lives. Those who are born without latent defects and are treated according to their individual needs, tend to perform better and also live longer. Batteries are very similar to people in that they experience a variety of conditions that control the length of their lives. Those who are treated well according to their individual needs tend to be happier and live a much longer life than the normal battery. Dr. David Feder of Electrochemical Energy Storage Systems conducted a study of battery replacements in the field and concluded that the reliability of the sealed battery was so bad that they should be removed from service after 2 years.Dr. David Feder of Electrochemical Energy Storage Systems conducted a study of battery replacements in the field and concluded that the reliability of the sealed battery was so bad that they should be removed from service after 2 years.These are some of the factors that control the reliability and life of a cell.Around a third leave the factory with a problem that will show up later.Standby batteries are designed to withstand about 90% fewer discharges than a marine or forklift battery.therefore how often and how deep the discharge can predict its life.

When the operating temperature rises the battery life is shortened dramatically.

The charge time need only be long enough to replace the effects of discharge. Over voltage charging causes an increase in the rate of deterioration and under charging causes a loss in capacity and irreversible sulfation of the plate surfaces. If the positive and negative plates come into contact with each other or if bridged by conductive material such as the conductive flakes that are naturally shed from the surfaces of the plate.

There are many kinds of open cells. Sulfation on the surface of the plate prevents the acid from reacting with the lead and causes a electrochemical open.Poor welds and other mechanical problems within the current carrying path will cause a voltage droop under load.Corrosion of the lead plates and within the current path will reduce the capacity.Dryout occurs when the liquid electrolyte is not covering the entire surface of the plate and causes a loss in capacity.In sealed batteries any plate warp or loss of compression between the acid soaked separator material and the plate will cause a serious loss in capacity.

Ruptures and leaks can cause the electrolyte and internal gasses to escape into the environment. These problems are caused by improper handling, improper support or by failure of the jar or post seals.Wear out is when the battery has met the design life and the capacity has degraded to 80%.Historically the is around 20% of the batteries placed in service. Thermal runaway as seen in the next slide is a result of increasing temperature with in the cell as a result of overcharge or the environment. When the battery cannot dissipate the heat as fast as it is being generated, the internal resistance is reduced which causes even more unconverted charge current and results in a rupture or in many cases an explosion.

An analysis of the causes behind batteries removed from service indicate that charging problems account for 31%, externally caused problems account for 17% and latent manufacturing defects account for 31%. This means that only 21% of the batteries placed into service lived a full expected life.

The APC individual cell charging can correct charging problems, clear soft shorts and double the normal life. This is a photo of thermal runaway.The cell circuit consists of five variable series resistor elements with a variable capacitor element in parallel with one of the resistive elements.

In this circuit Rxc- and Rxc+ are the external connections and include such variables as correct torque of bolts and corrosion at the interfacial surfaces.

Rn- and Rn+ are variables representing the condition of the plates. This includes natural deterioration that occurs as a function of age and usage, plus the sulfation formation that prevents good contact reaction between the active lead and the acid electrolyte.

Re is the variable resistance of the electrolyte solution. The resistance decreases as the cell is charged and increases during discharge.

Cp is a variable capacitance in series with the electrolyte. The capacitance increases as the cell is charged and decreases as the cell discharges.

Replacing cells that have been in service with new cells will cause charging problems. The new cells will have a lower internal resistance than the existing cells and this will cause the overall voltage to distribute unevenly. The AutoCap system will recognize the imbalance and correct the problem by supplementing the low charged cells. This graphic shows a four cell string being charged from a fixed 9 volt supply.

The management system recognizes that the cell on the left is not getting its 25% share of the applied charge voltage and charges it individually until the voltage begins to rise. When this happens, the overcharged cells voltage (on the right) will be reduced as the overall voltage is redistributed equally.

If every cell were identical in every respect, the 9 volts would divide up evenly and result in 2.25 volts across each cell.

In this example the cell on the left is undercharged at 2.1 volts and will not perform at full capacity during a discharge.

The cell on the right is being overcharged at 2.4 volts and will gas, lose electrolyte and deteriorate faster than the others.

The APC system will recognize the low cell and individually boost charge it until the voltage rises. As the voltage rises the overcharged cell voltage will drop as the overall 9 volts is redistributed within the string. This graphic shows a four cell string being charged from a fixed supply. Toward the end of the recharge, one cell reached full charge first and the individual voltage quickly increases into the gassing region. Note that as the lead cell voltage increases rapidly, the other cells voltage decrease and stop charging. In this example, there is one overcharged cell and three undercharged cells in the same string.

If every cell were identical in every respect, the 9 volts would divide up evenly and result in 2.25 volts across each cell.

In this example the cell on the left is undercharged at 2.1 volts and will not perform at full capacity during a discharge.

The cell on the right is being overcharged at 2.4 volts and will gas, lose electrolyte and deteriorate faster than the others.

The APC system will recognize the low cell and individually boost charge it until the voltage rises. As the voltage rises the overcharged cell voltage will drop as the overall 9 volts is redistributed within the string. The battery problem can be handled in many ways with various degrees of success.Most users want it both ways. They want the battery to always perform when needed, last 20 years and they do not want to spend any money on maintenance or testing. The more experienced users realize from their own horror stories (or ones that they have heard) that the battery is notorious for failing when the lights go out and causing the loss of time, data, product or other expense.

Automated Battery Management Systems can be justified many ways and any one can pay for the investment. Each user must ask themselves how much is at stake and look at the odds. The APC combination is a comprehensive approach that will not only perform the usual monitoring tasks but will also mitigate the potential for problems caused by under and over charging. The APC system is always busy. Either scanning the voltages, equalizing the charge state or conducting hourly stability confirmation testing. The system has the capability to activate remote alarms for individual voltages, changes in individual circuit resistances, individual state of charge and individual internal temperatures.The system will test and calibrate itself continuously, notify user when scheduled maintenance is due and alarm on external sensors wired to an auxiliary input.

The knee detection alarm backs up the countdown timer and notifies the user when the actual voltage under load is approaching the last 10% of capacity, regardless of the indicated and expected remaining time. External temperature probes are used for the ambient air and the case of a selected pilot jar.

During a discharge, the overall string voltage will initially decrease to the nominal voltage of 2 volts per cell and then follow by a very gradual decline for each unit of time.

Near the end of the batterys capacity the voltage begins to decrease more rapidly. This is called the knee of the discharge curve. If the battery is allowed to continue discharging past the Knee, the overall voltage will suddenly fall below the minimum usable value and possible reverse polarity which can damage the battery.

When the system recognizes that the voltage is decreasing faster than normal during a discharge, it will alarm and signal remotely. The Battery Management System consists of a processor running custom firmware controlling selector circuits, a voltage monitor, a current monitor and an isolated current source.The CPU executes the firmware instructions and selects individual batteries, closes the boost and alarm relays, operates the analog to digital converters and communications ports.The CPU compares the actual measured values with the alarm set points and the previously learned benchmark data.

The isolated charger is a transformer isolated DC supply that is set to a higher voltage than found on an individual battery.When the output is connected to one of the individual batteries, current will flow from the isolated charger into the selected battery.Since there is no reference to the other batteries, all of the current is directed into only the one selected.

The current monitor senses the amount of current that is accepted by the individual battery from the boost supply.The voltage drop across a 1 ohm resistor that is in series with the output of the boost supply is proportional to the amount of current delivered.The proportional voltage signal is sent to the processor for comparison with earlier current measurements of the same individual battery.Differences in current indicate instability in temperature, charge state or circuit resistance.

The voltage monitor converts the analog battery voltage signal to a digital format.The digital output is sent to the processor for comparison against the voltage alarm limits and evaluation of the individual battery deviation in actual voltage compared to the ideal average voltage.

The cell/jar selector uses relay contacts to connect the battery management system to one of the batteries. When the associated relay is pulled in, the system can monitor the voltage or route charge current to that individual battery.The selector is like a multi-plexer with multiple inputs and only one output.

In order to prove how much additional life can be realized when cells are charged individually, a controlled test was developed by the Battery Technology Center in Pittsburgh.

The FAA supplied 48 new VRLA cells for a controlled life test with the only variable being the method of charge.

The float group consumed 3500 amp-hours during the test compared with only 420 amp-hours for the ASCC group that was individually charged, but only as needed.

During the test it was apparent that each cell needed a different amount of energy to sustain a full charge. This chart shows how the required 420 amp-hours was distributed.The depth of corrosion of the positive plates confirms that individual charging adds 250% to the life compared with float charging.

Teardown analysis of sample cells from the float charged group showed that the rate of positive grid growth was more than 300% faster than the cells that were individually charged.

The float charged plates were severely warped and had chunks of active material falling out.

The APC charged plates had very minor warping and softening of the active material.

After the equivalent of 10 years and 16 discharges at the one hour rate, all of the original 24 Float cells had failed completely.The ASCC group still has 22 at or above 80 % capacity. The two missing cells were removed for teardown analysis.

The countdown timer output indicates exactly how much remaining backup time is to be expected. The exact amount of energy removed from the battery is recorded in the event file.

The individual cell/jar charging feature an APC exclusive. It is equivalent to having a charger for each cell that provides exactly the right amount of charge for exactly the right amount of time.

The independent life testing proved that this approach more that doubles the life of the battery.It also prevents charge related problems, such as over & Under charging and thermal runaway from developing. APC uses its isolated boost charger to characterize each individual battery with current which is the active part of an electrical circuit that changes in direct proportion to resistance.

Continuous monitoring and testing can find problems early in their development that would not be detected by the periodic approach.

If the equipment is in place, the critical individual voltage readings are automatically recorded during an unplanned outage. These readings can be evaluated after the event to determine how close the user was to a disaster before the power was restored. The ability to observe the system in operation, acknowledge alarms, download data and upload software makes the system reachable by remote experts or for routine data visits.

Since the APC has a full industrial IBM-PC with all of the standard ports and connectivity, inside the enclosure it can be connected to virtually any network scheme.

The same industrial PC makes it possible to store the normal resistance readings in a file and compare them with new readings as they are taken over time. If the new readings are different by more than the percentage set point, then the trend alarm contacts close. Unlike our competitors, the wires between the battery and the APC system do not require calibration or fixed length wires that must be doubled back and hidden in the conduit. We use spring loaded screw less lever terminals that are quick and do not ever require retightening.

The industrial PC will operate at 160 degrees F and has a solid state disk for storage of data and software.

Our competitors require that an external computer be connected to the box in order to make it work.

The short term trending lets you know if quick developing problems such as increased internal temperature are occurring on an hourly basis.

The short term trend resets itself automatically each time the equilibrium of the string is upset, such as after a discharge event.

The long term trend is used to track the gradual deterioration that occurs over much longer periods of time. The system compares monthly resistance values with the initial values and will alarm when any individual value exceeds 20%, indicating that it is time for a planned discharge test.In summary, the inherent internal and external factors relating to batteries can cause failure and premature loss of life. The battery management system can mitigate the external factors and alarm on problems.Management means that action is taken to get control of the variables that drive battery related problems and will extend the life beyond that which would be normally achieved.

The investment can be returned quickly by making the battery more reliable and making them live longer. Follow Tech scope of work. If Tab washers are not installed, refer to the BMS Retrofit kit instructions.