Aircraft Storage Batteries PDF

AIRCRAFT STORAGE BATTERY Maintenance & Servicing Practices Aircraft Electricity & Electronics Textbook Ch. 3: Aircraft Storage Batteries  Lead-Acid  Nickel-Cadmium  Li-ion ATAV-404...

AIRCRAFT STORAGE BATTERY Maintenance & Servicing Practices Aircraft Electricity & Electronics Textbook Ch. 3: Aircraft Storage Batteries  Lead-Acid  Nickel-Cadmium  Li-ion ATAV-404 1 Battery ratings - Capacity  Capacity is the measure of a battery’s total available current  A unit of current for a length of time  Aircraft Batteries are rated in Ampere-hours (AH)  The time required to fully discharge the battery multiplied by the current draw  To determine a battery’s actual capacity, all batteries are discharged at a 5-hour rate. ATAV-404 2 Battery ratings - Capacity  The relationships of ampere-hour capacity to the length of discharge  A slower discharge rate produces a higher total capacity (AH) ATAV-404 3 Battery ratings - Voltage  Batteries are rated by Voltage and Capacity  12 V or 24 V, with cells connected in series inside the battery case Cell Type OCV Discharge Lead-Acid 2.1 characteristics of a lead-acid Ni-Cd 1.28 cell Li-ion 3.5  Connect batteries in parallel if more amperage capacity is required. ATAV-404 4 Lead-acid Battery Maintenance Practices Safety precautions with Lead Acid batteries:  Protective gloves, apron, and glasses to be worn at all times in the battery shops  Neutralize spilled electrolyte with baking soda ATAV-404 5 Safety precautions with Lead Acid batteries  FLUSH AREA WITH WATER if spills occur  Metal jewelry, such as watches, chains, rings, and bracelets must not be worn while performing battery servicing ATAV-404 6  Lead Acid Battery Servicing  Remember to remove the Ground wire FIRST and connect it LAST  During recharge the battery will generate oxygen and hydrogen  Vent caps will allow gas to escape while containing electrolyte, but should be removed during charging ATAV-404 7 Charging a Lead Acid Battery  Connect charger leads to battery terminals...positive (red) to positive, and negative (black) to negative  Adjust charger to proper current, or voltage setting ATAV-404 8 Charging a Lead Acid Battery  Ensure proper electrolyte level in each cell. Add distilled water if required  Check and record Specific Gravity of each cell  Turn on charger Cell electrolyte level ATAV-404 9 Lead Acid Specific Gravity  The state of charge of a lead acid battery can be determined by checking the specific gravity of the electrolyte  A hydrometer is used to determine the Specific Gravity (S.G.)  The S.G. is the density of the electrolyte compared to the density of water ATAV-404 10 Specific Gravity of Lead Acid Batteries  The S.G. of the electrolyte decreases as the battery discharges.  During charging, the sulfates are driven from the plates, back into the electrolyte  This results in the electrolyte being converted to a higher concentration of sulfuric acid  Since sulfuric acid is denser than water the S.G. will increase during charging ATAV-404 11 S.G. of a Charged Lead Acid Battery  A lead acid cell should read between 1.275-1.300 when fully charged.  The battery should be charged until the cells are gassing freely and S.G. has remained unchanged for over one hour Performing a specific gravity test using a hydrometer. ATAV-404 12 Cold Weather Operations  All batteries perform better in warm environments than cold ones.  This is particularly true of Lead Acid batteries.  In cold environments, batteries should be kept fully charged to prevent freezing. ATAV-404 13 Cold Weather Operations  A cold battery will read higher S.G. and a hot battery will read lower than the actual S.G.  The temperature of the electrolyte must be taken into account when measuring the S.G. ATAV-404 14 Two Types of Battery Charging Systems Constant-Voltage Chargers Constant current for entire Current supply changes with state of charge cycle; voltage varies. charge. Requires careful monitoring 14V and 28V systems. to prevent overcharging. With battery fully charged its voltage Seldom used on in-service ~ charger voltage. lead-acid batteries. Electrolyte levels must be kept at Ni-Cd batteries use this desired levels. method. Most common type of ground-based and airborne charging system ATAV-404 15 Nickel-Cadmium Storage Batteries Constructed of wet cells Greater power to weight ratio than lead-acid CCV remains nearly constant during discharge A 20-cell nickel-caladium battery, top removed ATAV-404 16 NiCad Storage Battery ATAV-404 17 A Ni-Cd Battery Cell Nickel-cadmium vented cell cap Components of a typical nickel-cadmium cell. (a) Nickel-cadmium cell components, (b) Nickel-cadmium cell construction. (Marathon Battery Company.) ATAV-404 18  Ni-Cd Cell Cases and Covers  Most cell cases and covers are made from a nylon material of low water absorption.  To join cover to case, either a heat seal or tongue and groove construction and an electrolyte resistant sealing technique is used to provide a mechanically strong and leak-resistant joint. ATAV-404 19 Ni-Cd Construction - Plates  Nickel tabs sized for maximum current-carrying capability are then welded onto each plate in preparation for subsequent operations in which the positive and negative plates are connected to their respective cell terminals. ATAV-404 20 Ni-Cd Battery Chemistry  Negative plates are metallic Cadmium (Cd)  Positive plates are Nickel Oxyhydroxide (NiOOH)  Electrolyte is Potassium hydroxide (KOH) Discharge Charge 2NiO(OH) + Cd + 2H2O 2Ni(OH)2 + Cd(OH)2 Positive Negative Positive Negative Plate Plate Plate Plate ATAV-404 21 Ni-Cd Battery Chemistry  During discharge, electrons are delivered to the negative plates from the positive plates through the electrolyte.  Because OH ions are added to the electrolyte as rapidly as they are removed, the composition of the electrolyte does not appreciably change.  During charging the process is reversed ATAV-404 22 Ni-Cd Battery Cell Separator  A thin membrane made of a micro-porous fiber.  Prevents contact between the negative and positive plates.  Acts as a barrier membrane to keep the oxygen that is formed at the positive plates during overcharge from reaching the negative plates.  Oxygen at the negative plates would recombine with cadmium and create heat that might lead to thermal runaway.  Inhibits thermal runaway. ATAV-404 23  Ni-Cd Battery – Thermal Runaway  Caused when the battery experiences too great of a charge or discharge.  Can be controlled/stopped by isolating the battery from the electrical system.  Typically, a nickel-cadmium battery cannot overheat unless something internal is causing its temperature to rise.  The heat retained within the battery weakens and destroys the separator.  The cell’s electrical resistance lowers and decreases the cell’s voltage.  The battery receives excessive amounts of charge current from the aircraft’s charging system, which generates immense ATAV-404 heat within the battery. 24 Ni-Cd Battery Voltage Characteristics  Ni-Cd cells have a voltage of approximately 1.2 volts (1.28 OCV or 1.20-1.25 CCV)  Ni-Cd batteries maintain their full voltage until almost completely discharged  S.G. of the electrolyte remains unchanged at 1.30 (1.24-1.32) during charge and discharge conditions ATAV-404 25 Ni-Cd Battery Maintenance Procedures  Requires specific maintenance procedures-always follow the battery manufacturer’s recommendations during service.  Keep proper log entries.  Each battery should have its own specific maintenance record. CAUTION: Always observe precautions when charging nickel- cadmium batteries. Avoid accidental short circuits. The exposed cell connectors are very vulnerable to shorts from dropped tools or metallic jewelry. ATAV-404 26 Ni-Cd Battery Inspection 1. Inspect the battery case for cracks, distortion, or other damage. 2. Inspect the vent system (if installed) for proper airflow. 3. Inspect the cells and clean as needed. 4. Inspect the cell connectors for corrosion, cracks, and overheating. 5. Inspect the cell caps for proper O-ring and vent sleeve condition. Wash any dirty cell caps in clean, warm water. 6. Check the cell electrolyte level for proper amounts. ATAV-404 27 Ni-Cd Batteries – STATE OF CHARGE  Unlike some other rechargeable systems, the electrolyte in the nickel- cadmium battery does not significantly change in specific gravity during the charge and discharge processes.  As a result, hydrometer measurements of specific gravity cannot be used to determine the state of charge of the battery.  The electrolyte for a nickel-cadmium battery is a solution of 70 percent distilled water and 30 percent potassium hydroxide, which gives a specific gravity of 1.3. ATAV-404 28 Ni-Cd Batteries - STATE-OF-CHARGE  The state of charge of a Ni-Cd battery can only be determined by putting a known amount of charge into it  Ni-Cd batteries are typically charged to 140% of their Ampere Hour Rating.... ATAV-404 29 Ni-Cd Batteries - STATE-OF-CHARGE  For example, a 50 AH battery would have 70 AH of current applied to it  A common procedure is to charge the battery at its 5 hour rate, for 7 hours ATAV-404 30 Ni-Cd Batteries - Servicing  Water additions to adjust the liquid level should be made immediately after charging or after the battery has been permitted to remain in a state of rest for a minimum of three hours after charge.  Never adjust the electrolyte level after discharge unless abnormally high voltage readings (greater than 1.5 volts) are encountered immediately after placing a discharged battery on charge. ATAV-404 31 Ni-Cd Batteries - Servicing  ONLY DISTILLED WATER SHOULD BE ADDED TO THE BATTERY ATAV-404 32 Photos: https://i5.walmartimages.com/asr/3eb5ed4b-deca-4bc3-85c6-9894a4cb8f5e_1.234c6909ceeaa5c3cb9e7bef1342f00d.jpeg?odnHeight=450&odnWidth=450&odnBg=FFFFFF Cell Imbalance  Occurs during the recharging of the battery by the aircraft’s constant- voltage charging system  Can be caused by differences in temperature, charge efficiency or varying self-discharge rates in cells  Results in a temporary loss of battery capacity  Corrected by reconditioning (deep cycling) the battery as per manufacturer’s recommendations ATAV-404 33 Ni-Cd Battery Servicing  Protective gloves, apron, and glasses to be worn at all times in the battery shops  Neutralize spilled electrolyte with Boric Acid  FLUSH AREA WITH WATER if electrolyte spills  Metal jewelry, such as watches, chains, rings, and bracelets should not be worn while performing battery servicing 34 Ni-Cd Battery Servicing  Cell vents do not need to be removed during the charging process  Neutralize spilled electrolyte with Boric Acid, and flush area with water 35  ATAV 404 Ni-Cd Battery Servicing Procedures  Batteries are routed to the Ni-Cd shop for the purpose of servicing, so they can return to service on aircraft, or be used as ground power supplies for work in the hangar.  Depending upon their condition, batteries may be tested, recharged, and returned to service, or…  Batteries may be tested, and “DEEP CYCLED” Photos: http://trimecaviation.com/wp-content/uploads/2017/06/Dynamo_Aviation-3313-2.jpg 36 Servicing Flow Chart  ATAV 404 Ni-Cd Battery Shop Safety Procedures  PPE to be worn at all times in the battery shops  Neutralize spilled electrolyte with boric acid, and flush area with water  Know the location of boric acid, and eyewash station  Be very diligent in watching for the symptoms of a THERMAL RUNAWAY 38  ATAV 404 Ni-Cd Thermal Runaway  Most likely to occur at the beginning and end of the charging process SYMPTOMS OF THERMAL RUNAWAY  Decrease in cell voltage  Cells become warm  Decrease in resistance  Increase in current draw 39  ATAV 404 Ni-Cd Thermal Runaway IF YOU SUSPECT A THERMAL RUNAWAY 1. SHUT OFF THE CHARGER 2. LEAVE THE ROOM IMMEDIATELY! 3. NOTIFY A PROFESSOR 40  ATAV 404 Ni-Cd Battery Record Keeping  Battery log sheets MUST be filled out  Make note of cell changes, hot cells, and cells which require water to be added  Record cell voltages hourly, but monitor cell voltage continually  Use the reference material provided in the shop, and ASK a professor if you are uncertain about procedures 41  ATAV 404 NiCad Battery Servicing - Step-by-Step Procedure* * Consult Manufacturers Use and Maintenance Guidelines  If the battery is received in a charged condition, an electrical leak check should be performed. Prior to discharge, this test detects current leakage from the cells to the battery case. A leakage exceeding 50 mA measured from any positive cell connection to the case is usually excessive.  If the battery arrives in a discharged state, a leak test should be performed after charging. The current flowing from the cell to the battery case (electrical leakage) is usually caused by excessive liquid on top of or around the cells. 42 Nov 20  ATAV 404 NiCad Battery Servicing - Step-by-Step Procedure* * Always refer to manufacturer’s maintenance data STEP 1 Determine proper charger settings... if in doubt, calculate which setting would result in 140% of the AH rating being put into the battery Connect battery to charger, and place on “Main Charge” Check cell voltages immediately Add 5-10cc of distilled water to any cell reading more than A typical nickel- 1.5 volts cadmium WATCH FOR SIGNS OF battery THERMAL RUNAWAY charger/analyzer (The Christie Corporation.) 43 Nov 20  ATAV 404 NiCad Battery Servicing - Step-by-Step Procedure STEP 1 continued  Continue on main charge until all cells measure between 1.55-1.75 Volts  Continually monitor cell voltages and record these voltages hourly When done… 1. Turn off charger 2. Disconnect battery 3. Check leakage current between positive terminal and battery case  If this “Leakage Current” exceeds 100mA, battery must be deep cycled  If less than 100mA, begin capacity test 44  ATAV 404 NiCad Battery Servicing - Step-by-Step Procedure Step 2 - Capacity Test  Connect the battery to the analyzer, and begin the “Discharge Cycle”. Monitor cell voltages  If the “Low Voltage” light illuminates or if any cell drops below 1.0 volt in the specified discharge time, the battery has failed the Capacity Test 45  ATAV 404 NiCad Battery Servicing - Step-by-Step Procedure Step 2 continued  If the battery Passes the Capacity Test, allow the battery to recover for at least 1 hour, then proceed to “Step 4” (Final Charge)  If the battery Fails the capacity test, perform a “Deep Cycle” as follows... 46  ATAV 404 NiCad Battery Servicing - Step-by-Step Procedure Step 3 - Deep Cycling  Place analyzer selector switch to the “MANUAL DISCHARGE” position  Monitor cell voltages as battery discharges  When a cell drops below 0.5 Volts, short that cell with proper shorting strip  A landing light may be used to expedite the discharge process  When ALL cells are shorted, battery should be left to rest for at least 3 hours 47  ATAV 404 NiCad Battery Servicing - Step-by-Step Procedure After Battery Has Fully Discharged  Remove shorting strips  Wash battery with water and a non- metallic brush  If the battery failed the “Leakage Current” test, it should be disassembled, all cells washed, reassembled, and dried with compressed air  The battery is now ready for charging A Megaohmmeter used to test for leakage of a nickel-cadmium battery 48  ATAV 404 NiCad Battery Servicing - Step-by-Step Procedure Step 4 - Final Charge  If the battery passes the Capacity Check or has been deep cycled, it should be allowed to recover for at least one hour, and then recharged  To recharge, set to “Main Charge” and allow it to complete the whole charge cycle MONITOR FOR THERMAL RUNAWAY! 49  ATAV 404 NiCad Battery Servicing - Step-by-Step Procedure Step 5 - Completion of Paperwork  When fully recharged, tag the battery, and place on the “Serviceable Rack”  Ensure all log sheets are completed NOTE: Since the state of charge of a Nicad cannot be determined, it is essential that all paperwork be completed, to avoid unnecessary repetition of work already performed 50 11/5/2019  ATAV 404 Battery Servicing Areas  Nicads and lead acid batteries have electrolytes which are capable of neutralizing one another….EVEN THE FUMES!!  For this reason, they should not be serviced in the same area  Tools used on one type of battery should not be used on the other. Photos: https://img.haikudeck.com/mg/U4kVaPhDQF_1409752484880.jpg 51  ATAV 404 Battery Ventilating System and Sump Jars  Many aircraft employ a battery venting system which provides an airflow over the battery.  This provides cooling and removes gasses.  A Sump Jar containing Boric Acid or Baking Soda Battery ventilating system may also be employed to neutralize discharged gasses.  Vent lines should be checked to ensure they are not obstructed, and neutralizing agent replaced on a regular basis. 52 Battery Chemistries in Aviation Lithium-ion Storage Battery Lithium-ion Storage Battery Battery quick-disconnect Lithium-ion battery used on an Airbus A-350  ATAV 404 Battery Servicing Resources  General Text  Aircraft Electricity and Electronics  LRC Videos !!! USE THEM !!! 56