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BATTERY CHARGERS AND BATTERIES FOR DC AND AC BACK-UP                                                   POWER SYSTEMS      ...
in float service. However, even with the best chargers,               requirements. The recombinant battery is often refer...
expensive the rectifier. This is usually not a system              The negative temperature compensation circuit increases...
The “float” “recharge” voltage selection can be accomplished        connecting a f l YO regulated battery charger across t...
VII. MANUAL METHODS FOR MONITORING                            . Float voltage and time at float                 BATTERIES ...
battery has already been documented as a “failed battery, it      systems, alternative energy & solar electric systems, an...
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Battery charging and backup


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Battery charging and backup

  1. 1. BATTERY CHARGERS AND BATTERIES FOR DC AND AC BACK-UP POWER SYSTEMS Copyright Material IEEE Paper No. PCIC-2001-13 Jack Ripley M.T. (Rick) Ansari Jerry Dehn, P.E. Member, IEEE Member, IEEE Member, IEEE Battery Service Co. Saudi Aramco Industrial Data Systems 11634 Wilcant Ln. P.O. Box 97681 5031 Woodham Drive Cypress (Houston), TX 77429 Daharan, 3131 1 Suite 360 USA Saudi Arabia Houston, TX 77073 USA4bsfract - The purpose of this paper is to provide support in . Record keepingspecifying batteries and battery chargers for both DC and AC . Battery Disposallack-up power systems. II. BATTERY TYPES‘ndex Terms - Battery Charger, Battery, UPS Systems A brief description of the various battery types is given 1. INTRODUCTION for the purpose of providing an understanding of the problems related to various types of batteries. There Many times in AC and DC power systems considerable are three basic battery types being used today indtention is given to the load parameters such as AC ripple industrial float service applications. In the DC bus, DC voltage regulation, and system RFI. The guaranteed life of each type ranges from 1-20 years However, too often the requirements conditioned by the for the flooded vented lead acid, 1-25 years for the flooded )attery (i.e. DC voltage window) as well as the conditions vented nickel cadmium and 1-20 years for the recombinant.:hich cause premature battery failure are overlooked. In the (valve regulated leadqsid VRLA) battery. Although not llajority of cases when a DC system fails it is because the recommended for float service applications, a fourth type Jatteryfailed to perform. This could be the natural result of of battery is sometimes used; the flooded vented lead acid:n old battery finally just “dying”. In which case no one would (SLI) (Starting, Lighting and Ignition) battery. le surprised, and in fact good preventative maintenance 1) Starting, Lighting and Ignition Battery: Thevould have identified a weak cell or cells allowing the battery flooded vented lead acid (SLI) battery is either a standardo have been replaced before system failure. However, all automobile/truck battery, or a slightly modified derivative of00 often the battery failed to provide its expected life the same. They are characterized by thin plates, (even Jecausethe conditions, which cause premature battery the “thick plate” versions have much thinner plates thanailure, were not recognized and addressed in the their stationary counterparts), high specific gravity.pecification phase. electrolyte (1.260-1.300), high energy density and Today’s industrial batteries are offered with a guaranteed relatively short life (usually 1-3 years). These batteries are i e of 90 days to 5 years full replacement and with prorated designed to be charged from an engine alternator. They iarranties up to 25 years. With this wide product quality are expected to be on charge 2-4 hours per day, everyday; ange, the price range is also very wide. and when they are not being charged they are expected to his paper details pertinent information relating to: set idle (open circuited) and not connected to a load. Battery types This type of operation is considerably different from that Typical DC load recommendations typically seen by a stationary battery. When placed in a Typical charger features constant float charge application they experience unique Site and load conditions that effect battery problems. When charged at their desired voltage, but in a maintenance and battery life continuous float application, they experience overcharge, Charger features which improve battery excessive gassing, accelerated plate shedding and maintenance and battery life resulting shortness of life. When the float charging voltage Requirements when parallel chargers andlor is reduced to alleviate this overcharging, they suffer from batteries are used. undercharge, plate sulfation and again, shortness of life. Manual methods for monitoring batteries We will address some optional features, that can be Automatic battery monitoring specified for the charger to improve the life of SLI batteries OICH37265 -139-
  2. 2. in float service. However, even with the best chargers, requirements. The recombinant battery is often referred to asthey will probably have shorter lives than an identical SLI “maintenance free” by suppliers but has been re-named “nonbattery in your own family car. maintainable” by many users. While it is maintenance free in 2) Flooded Vented Lead Acid: The flooded vented the sense that you do not have to ever add water to the cell, itlead acid stationary battery will last much longer than its is non-maintainable in the sense that you cannot ever addSLI counterpart. Because it is usually designed for IO, 15 water to the cell. Other maintenance functions such asor even 20-year life, the plates are much thicker (less plate periodic cleaning of the terminal connections, re-torquing ofsurface per pound of active material) and the specific the terminal connections, etc. must still be performed.gravity of the electrcllyte is considerably lower (usually Two types of maintenance free construction are used. In1.215 -1.250) which results in much lower grid and plate both types the electrolyte is immobilized. In the “Gelled”corrosion rate, especially at operating ambient temperatures type, silica is added to the sulfuric acid electrolyte to form ahigher than 25°C. paste or gel. In the “Absorbed Glass Mat” (AGM) type, the These cells are provided in either lead calcium or lead electrolyte is retained in a very fine fiberglass mat at aboutantimony grid construction. The lead calcium grid exhibits 80% saturation. The advantage of both types is thelower float currents and therefore lower water loss resulting in elimination of electrolyte stratification. The disadvantage islower hydrogen emission. The lead antimony grid is typically the inability to perform hydrometer readings for routineI-year full/l5 year prorated as compared with a I-year fuW20 maintenance diagnostics or to add water as the electrolyte isyear prorated life of its lead calcium counterpart. depleted by normal gassing. Because all batteries become However, at elevated temperatures (30°C or greater) the less capacitive as they deteriorate, a measure of thelead antimony cell v d l outlast the lead calcium cell. The lead batteries’ ability to filter AC ripple can provide much of theantimony cell is also offered in low antimony alloys of same diagnostic information as the old hydrometer test.selenium or tin. The most popular is defined Commercially as Another battery feature is more a matter of construction“Lead Selenium” in which the grid is an alloy of lead, technique than of battery type. However, it is an item that isantimony and selenium. This produces a plate with float many times specified because it can result in improvedcurrent characteristics very near the lead calcium but is not battery life. This is a result of the type of cell formation usednearly as adversely effected by deep discharges, numbers of in the initial charging process.cycles or ambient temperature. All battery plates must be “Formed” after casting. This is a 3) Flooded Vented Nickel Cadmium: The flooded process where the positive and the negative plates becomcvented nickel cadmium battery is distinguished by its rugged electrically charged to form a battery cell. The simpler, lessconstruction, high performance, very long service life, and expensive method is to install the complete electrode groupimmunity to corrosiomn of the active materials. into the cell container, fill it with acid and then “form” (thc It is the longest life battery in industrial applications. It is initial charging process) the cell. This method of “Jaralso the most forgiving of all batteries in response to Forming” causes each cell to form up independently, resultin5overcharge, underc:harge, temperature extremes, vibration, in individual differences in the various parameters of eacketc. It also has the highest initial capital equipment cost as cell. As more cells are interconnected in series or parallel tccompared to all other industrial battery types. form the total battery, these differences begin to add ur 4) Recombinant Lead Acid: The recombinant lead acid resulting in total battery deterioration.battery, commonly known as “Valve Regulated Lead Acid Another method of cell formation is “Tank Forming”. In tank(VRLA)” is a float service stationary battery originally formation many cell electrode groups are inter-connected an1designed for short high rate discharges (10-15 minute UPS immersed in large tanks of acid and given their initial formintapplications and under 1 minute switch gear applications). charge resulting in similar formation processes. The Some manufacturers have expanded part of their individual electrode groups are then installed in theirrecombinant produd line to lend itself to long slow discharge individual cell containers. This process results in balancec(station and communication) applications. The products cells and therefore much betters life, as the individual cell:designed for short fast discharges are usually very good for are series or parallel interconnected to form the complet:gen set cranking. .4s with all lead acid batteries, care must taken in applications involving wide temperature ranges,especially high temperatures. This type of battery is much 111. TYPICAL DC LOAD RECOMMENDATIONS more susceptible to higher operating temperatures above 30°C. The VRLA battery can also undergo rapid destruction The load parameters, which are typically specified, are:and failure if subjected to higher than recommended float . DC Voltage Regulation (usually +-1-2%)voltage and unstable charging condition. For achieving long . DC Ripple (usually I-2% rms) life, this battery should be used in a temperature-controlled Note 1. Recombinant batteries will have improved life if environment with a stable ambient temperature of 20-25°C. this ripple is kept under 100mV. The recombinant battery meets higher shock and vibration Note 2. If communication equipment is part of the DC specs than flooded lead acid batteries. Some designs are load it is desired to keep this ripple under 30mV. non-position sensitive and can be installed in vertical or . RFI: The lower you specify this number the more horizontally stacked arrangement to minimize floor space -140-
  3. 3. expensive the rectifier. This is usually not a system The negative temperature compensation circuit increases theconcern except in communication equipment. battery charging voltage as the battery temperature falls and reduces the battery charging voltage as the battery IV. TYPICAL CHARGER FEATURES temperature rises. The charging voltage compensation is typically 5 mV/”C. It is more common that a typical battery charger will be 2) Number of Discharges: Not much can be done toequipped with the following accessories: reduce the number of discharges. This is primarily dependent. DC Voltmeter on the reliability of the AC power supply to the charger.. DC Ammeter However, if a large number of discharge cycles are. AC Input Circuit Breaker anticipated, it might be of value to consider either nickel. DC Output Circuit Breaker cadmium or lead antimony.. AC Failure Alarm Relay & LED 3) Depth of Discharges: Numbers of cycles and depth. High Voltage Alarm Relay & LED of discharges do not have a serious impact on the life of. Low Voltage Alarm Relay & LED nickel cadmium batteries. Depth of discharges do impact the. Ground Fault Alarm Relay & LED’s life of lead acid batteries, with serious impact on the life of. Charger Failure Alarm Relay & LED lead calcium batteries.. FloaffEqualize Switch 4) Site Shock Specifications: Site shock specification Various other options that may or may not be specified, is usually referred to in relation to uniform building code depending upon the operating conditions and plant (UBC) seismic zone 0-4. This has to do with the ability of the operating philosophies. battery and battery rack to withstand an earthquake of a. Circuit Breaker Open Alarms specific magnitude. Another shock condition, which is also of. AC Pilot LED concern, is the low amplitude, low frequency vibration that is. FloatlEqualize LED’s many times experienced around heavy equipment.. High Voltage Shutdown The battery’s ability to withstand vibration or shock varies. Charger in Current Limit Relay & LED with battery types. Following is a list from least sensitive to. Low Charger Current Relay & LED the most sensitive:. Battery Discharging Relay & LED . Nickel Cadmium. Discharge Pre Alarm Relay & LED . Recombinant (Gel). End of Discharge Relay & LED . Recombinant (AGM). Battery High Temp Relay & LED . Lead Antimony (Wet). Battery Disconnected Relay & LED . Lead Calcium (Wet). Load Disconnected Relay & LED. Common Alarm Relay & LED VI. CHARGER FEATURES WHICH IMPROVE. Audible Alarm With Reset BATTERY MAINTENANCE AND BATTERY LIFE. Battery Negative Temperature Compensation With OnIOff Control 1) Regulation: The charger should maintain the output voltage of the battery charger to within +, - 1% maximum. V. SITE AND LOAD CONDITIONS THAT Too high of a voltage drift can cause excessive heating within EFFECT BATTERY MAINTENANCE AND the battery. Recombinant batteries are more sensitive to this BATTERY LIFE voltage drift than wet flooded batteries because the lost electrolyte due to gassing cannot be replaced, and There are several site and load conditions that impact consequently the battery will experience reduced capacity. lattery life. The most important are: 2) Voltage Settings: To get optimum life from any of Ambient Temperature the various battery types available, they must be kept fully Number of Discharges charged without overcharging. The desired charging voltages Depth of Discharges of the various battery types (or similar types with different Site Shock Specifications specific gravity electrolyte) are of course different. 1) Ambient Temperature: Lead acid batteries are much However, they can each be charged by the same battery ]lore sensitive to high temperatures than nickel cadmium charger by simply setting its “float” and “recharge” voltage to iatteries. Also lead calcium batteries are more sensitive than the desired setting: ead-antimony batteries. If the batteries are to be installed in “Float” VIC“ “Recharge” VIC :n area with temperature swings, the battery chargerkectifier Flooded SLI @ 1.265 Sp. G 2.25 2.33 ;hould be equipped with “negative temperature” Flooded L.A. Stationary 2.2 2.33 :ompensation control to provide much improved battery life. Flooded L.C. Stationary 2.20 2.30 Flooded NI Cad 1.42 1.60 VRLA 2.25 2.30 -141-
  4. 4. The “float” “recharge” voltage selection can be accomplished connecting a f l YO regulated battery charger across the by means of a simple toggle switch, a manual initiate timer, batteries in a controlled temperature room and then raisingan automatically initiated timer, an automatic voltage sensing the charger voltage 4.2% for half of the year and reducing thecircuit, an automatic current sensing circuit or a measure of charger voltage 9% the other half. As you can imagine, thisremaining battery Al-l capacity. would rapidly destroy the battery. There are times when in order to match the battery float and Note: If the battery is mounted in a different environmentrecharge voltages with the desired load voltage for the from the battery charger, the temperature sensing devicesystem, the number of cells in the battery may be increased must be remote mounted on a pilot cell at the battery.or decreased as required. Also at various times it is desired 5 ) Charger Sizing: If a relatively large capacity batteryto use “cemP‘ circuits or DC/DC converters. A counter is being charged from a very small capacity battery chargerelectro- (trickle charge), the plates of the battery will take on what ismotive force (cemf) circuit connects a series of diodes referred to as a “surface charge”. They will appear to be fullybetween the battery ;and load. This low loss device drops the charged. However, because the charger is too small tohigher battery voltage down to the desired load voltage. provide sufficient energy to force adequate electron flowWhen the AC power to the charger is lost and the battery homogeneously through the plates, some of the plates in thebegins to discharge, the diodes are shorted out with DC plate group will accept a surface charge allowing a currentcontactors to prevent the DC load voltage from dropping to path around their surface and through the electrolyte to thethe end voltage and :;hutting down too soon. adjoining plate surface. Open circuit voltage tests, low load 3) Ripple: AC ripple imposed on the DC bus can not voltage tests or hydrometer tests of a battery in this conditiononly can affect the [IC load, it also causes heat inside each will probably not reveal the problem; yet when high currentbattery cell. The following maximum ripple voltages should loads are energized and draw large currents, the voltage ofbe considered: the undercharged battery will drop and the load will shut. 2% RMS (Wet Flooded Batteries) down.. lOOmV RMS Recombinant Batteries For most industrial applications the minimum charger size is.30mV RMS Communication Loads approximately 10% of the battery AH capacity. The chargerNote: Whatever AC ripple is advertised assumes that a size should be increased to accommodate any additionalbattery with AH capacity equal to four times the chargers continuous loads, i.e. lamps, instrumentation, heaters, etc.,current capacity is connected to the charger. In the event the which are connected across the DC bus.desired ripple is wanted with a smaller battery connected or Almost all battery chargers have a current limit circuit whichwith no battery connlected, this must be specified. Reducing protects the charger from destroying itself into a lowthe AC ripple will require increasing the size of the chargers impedance load (discharged battery). Attention should befilter circuit. This will probably increase the cost and perhaps given to whether this current is available at full voltage or at aincrease the charger enclosure size. reduced voltage. Some chargers advertise a rather high 4) Negative Temperature Compensation: When the current limit capability, while in fact they will produce thatbattery is to be used in an area where the ambient current only at near zero volts. If the current limit capacity oftemperature varies outside the 21-26°C temperature window the charger is going to have value, it must be at a voltagemuch improvement in battery life and reduced battery sufficient to recharge the battery and power the load.maintenance can be accomplished by speciving “negative The recommended formula for charger sizing is:temperature” compensation on the charger. Ic=AH/EFF/HR+I loadWhen a negative temperature compensation circuit is Ic=Charger current ratingprovided on a battery charger, a compensation “on/oW AH=AH’s removed from batteryswitch should be included in order to assist in charger set-up EFF=Battery recharge efficiencyand monitoring of regulation. (Typical 0.9 Lead Calcium, 0.85 Lead Antimony/Selenium, 0.7 All batteries have i3 negative temperature coefficient. Nickel Cadmium)This means that to maintain proper charge on the battery HR=Hours to rechargeplates, the charger koltage should be increased I load=Continuous load currentapproximately 0.23% per “C drop in battery temperature and When a relatively large charger or chargers are providedthe charger voltage should be reduced approximately 0.23% across the DC bus care must be taken to assure that not tooper “C rise in battery temperature. much current can be forced into a near discharged battery Of In some stationary applications, it is not uncommon to group of parallel batteries. A standard rule of thumb is notexperience a wide range of ambient temperature conditions. more than 25% of the batteries AH capacity should be With a range of -17 to +40°C the charger voltage would provided as the charging current. (Not more than 25Aneed to be adjusted +9 to -4.2%. Failure to make these charging current into a 100AH battery).adjustments will result in increased battery maintenance and Each charger has its own current shunt to control its currenireduced battery life. limiting function, however many times an additional curreni To use a non-temperature compensated battery charger in sensing device shall be provided in each battery string tothe above example would effect the battery the same as force each charger into current limit when the desired maximum battery charging current is reached. -142
  5. 5. VII. MANUAL METHODS FOR MONITORING . Float voltage and time at float BATTERIES . Equalize voltage and time at equalize . Temperature 1) Visual Monitoring: Many factors regarding battery . Water loss (flooded)condition can be visually observed. Some of the more . No. of dischargescommon things to be looked for are: . Depth of discharge There are other battery monitors which also provide some. Terminal Corrosion maintenance function such as providing a small trickle current. Loose Terminals to help recharge a less than charged cell. There are also Note: It is a good policy to re-torque the battery intercell connections every three years due to metal creepage in monitors which measure the current out of the battery lead acid cells. integrating it with time to maintain a log of actual AH’S. Electrolyte Level (Wet Flooded) remaining at any moment in time. This monitor is then set with a thrushold of 10% discharged when it is used to switch. Room Temperature the charger voltage to “equalize” and measure the current 2) Voltage: A calibrated volt-ohm meter can be used to back into the battery, again integrating it with time andmeasure and record the following battery parameters: dividing by the battery recharge efficiency and switching the. DC Voltage charger back to “float” when the battery is fully recharged.. AC Ripple 3) Hydrometer: A hydrometer specific gravitymeasurement of the electrolyte for wet flooded lead acid cells X. BATTERY DISPOSALprovides a reasonable measure of the batteries percent stateof charge. The specific gravity reading is not an indication of The purpose of this section is to provide some help inthe remaining battery potential capacity, but only the existing dealing with the concerns of “used battery” disposal. We% of charge at the time. This test of course can only be make no attempt to address the legal or technical aspects ofperformed on wet flooded batteries. the problem. We wish only to point out some of the areas of Both an indication of the state of charge as well as an concern. Consult the environmental groups within your ownindication of the battery condition can be measured by the company to provide the guidance needed to comply withbatteries ability to filter AC ripple. present and future EPA and local regulations. Thus by measuring the AC voltage ripple in mV across It is our understanding that all batteries, which have beeneach cell with a simple digital AC voltmeter you can declared or documented as “scrap”, “failed, “waste”, “spent”determine any weak cell or cells in the string. The higher the or any designation suggesting they are no longer “useableAC ripple, the weaker the cell. batteries”, are by EPA regulation considered “hazardous waste” and must be dealt with accordingly. VIII. AUTOMATIC BATTERY MONITORING This means the prgduct so designated, could only be moved by a licensed hazardous waste transporter and then only to At many sites it is desired to have automatic monitoring of an EPA approved (licensed) hazardous waste recyclingthe cells in the battery for both maintenance, warranty and facility. It is further our understanding that if the “failed” product is turned over to an EPA approved recycler, the EPAcell or battery replacement.The primary parameters, which can be monitored, are: andlor local environmental agencies have seven (7) years in. Battery voltage which they could tighten their requirements or controls and the recycler would have to go back and clean up the waste. Battery Cell Voltage. Battery Temperature for the past seven years. If the recycler complied with this. Battery Cell Capacitance requirement, all would be well and good. However, if the. Battery Cell Voltage Drop Under Load recycler was unable or unwilling to comply with the new Another function, which can be automatically provided, is requirements, the Superfund could step in and perform thethe ability to manually or automatically connect a DC load task and pass their clean up charges on to the originalbank and measure the above parameters. companies who had turned the “failed” product to the recycling company. It appears then that large corporations (potentially deep IX. RECORD KEEPING pockets), not only need to be concerned that the recycler is approved and in compliant with all current requirements, but There are many battery monitors available today, which also that the recycler is financially strong enough andprovide considerable monitoring, and data logging for battery sufficiently committed to maintain compliance with all futuremaintenance personnel. requirements. This is one of the primary reasons we have The following records are of value for both maintenance chosen to work so closely with major battery manufacturersand warranty purposes: when recycling. Again, we emphasize it is our understanding that if the -143-
  6. 6. battery has already been documented as a “failed battery, it systems, alternative energy & solar electric systems, andcan only be transported by a “licensed hazardous waste stationary batteries. Rick is an instructor for the UPS, DCtransporter”, and they can only transport the battery to a systems, and Batteries courses offered by Saudi Aramco“licensed hazardous waste recycling facility”. Therefore, you for training and development of Company professionals.may desire to have the Bill of Lading specify “Used Batteries” Rick has authored several papers on application ofand not “Failed”, or “Scrap” batteries. batteries and alternative energy systems. Rick received his BSEE from Oklahoma State University, Stillwater. He XI. CONCLUSION is a Registered Professional Engineer in Texas and a member of IEEE Power Engineering Society. As down time gets more expensive while maintenancebudgets seem to diminish it is becoming increasingly important J. W. Dehn, PE is an Engineering Manager for IDSthe power equipment as well as the monitoring equipment be Engineering’s Houston Division. Mr. Dehn is an Electricalspecified in order to eliminate as many potential problems as Engineer registered in the state of Texas, with job dutiespossible. This becomes even more important with the that include facilities automation, SCADA systems, PLCincreased use of VRL.A batteries. based control panel designs, ESD logic, motor controls, As discussed with careful attention during specification, substation design, switchgear selection, preparation ofmany of the potential problems which effect premature system grounding networks and instrumentation design for liquidfailure can be reduced or eliminated. and gas pipelines. He received a BSEE from the University of Oklahoma and is a member of ISA and IEEE. NI. REFERENCES1. George Wood Vinal, “Storaqe Batteries” by John Wiley & Sons, Inc. 19512. T. R. Crompton, 33atterv Reference Book”3. S. Uno Falk & Alwin J. Salkin “Alkaline Storage Batteries”4. IEEE 446-1987, “EEE Recommended Practice For Emerqency And Standby Power Systems For Industrial And Commercial Applications”5. IEEE 602-1986, “EEE Recommended Practice For Electrical Systems In Health Care Facilities”6. IEEE 450-1980, “EEE Recommended Practice For Maintenance, Testing And Replacement Of Large Lead Storacle Batteries For Generating Stations And Substations”7. IEEE 1106-1995, “IEEE Recommended Practice For Installation, Maintenance, Testinq And Replacement Of Vented Nickel Cadmium Batteries For Stationary Applications” XIII. VITAJack Ripley is the president of Battery Service Co. ofCypress, (Houston) TX. His past experience includesengineering and management for battery, battery chargerand UPS manufacturers for more than 30 years. Mr. Ripleyreceived his BSEE from California State PolytechnicUniversity. He is past president of EGSA and a member ofIEEE.M.T. (Rick) Ansari is an Engineering Specialist in theConsulting Services Department of the Saudi Arabian OilCompany (Saudi Arabia), Dhahran, Saudi Arabia. He isinvolved in the development of standards andspecifications for industrial rectifiers, UPS systems, staticswitching devices, standby power systems, backup power 144 -