Ni-Cad Servicing PDF 2021

9/13/2021 Ni‐Cad Ni‐Cad Charging: When a voltage is applied to the battery with such polarity that the positive termin...

9/13/2021 Ni‐Cad Ni‐Cad Charging: When a voltage is applied to the battery with such polarity that the positive terminal of the source goes to the plate having the nickel hydroxide Servicing (positive), and the negative terminal of the source goes to the plate with cadmium hydroxide (negative), oxygen is driven from the negative plate, leaving metallic cadmium. The nickel hydroxide on the positive plates accepts this oxygen and becomes more highly oxidized. 2 Ni‐Cad Ni‐Cad WATER LOSS END OF CHARGE VOLTAGE As the battery approaches the end of charge The end‐of‐charge voltage, measured while and during overcharge, gassing occurs. The the cell is on charge, depends upon its amount of water loss through electrolysis temperature and the method used for depends upon the number of ampere hours of charging it. current passed through the battery during As an example, a cell in a 19 cell battery being overcharge. charged at room temperature at 28.5 constant voltage would read about 1.5 volts at the end of charge. 3 4 Ni‐Cad Ni‐Cad Under a constant current charging condition The most effective way of charging a battery is this value would depend upon temperature by putting current back into it at a constant and charge current: rate. at the end of 7 hours charging at the 5‐hour rate, the voltage of a standard cell would be Constant‐current chargers adjust the applied about 1.58 volts. voltage in order to maintain a constant‐ current. 5 6 1  9/13/2021 Ni‐Cad Ni‐Cad The time required to charge a nickel‐cadmium The open circuit voltage of a vented nickel‐cadmium battery by the constant current method depends battery cell is generally accepted as 1.28 volts. on the size (capacity in ampere‐hours) of the The open circuit voltage of a battery would be 1.28 battery, its state of charge, and the magnitude of volts times the number of cells in the battery. This the charge current. value is the same regardless of the size or shape of One of the recommended methods is to charge a the cell although it does depend upon such factors as the temperature of the cell and the elapsed time discharged battery at the 5‐hour rate for 7 hours, since its last charge. thus providing sufficient overcharge of (40%). 7 8 Ni‐Cad Ni‐Cad Immediately after removal from a charger, the CLOSED CIRCUIT VOLTAGE voltage is high but slowly settles and The closed circuit voltage of a vented nickel‐ maintains a value of about 1.35 to 1.28 volts cadmium cell is that voltage read immediately per cell. The open circuit voltage does not after a load is connected and is less than its indicate the state of charge. open circuit voltage. You cannot use a voltage measurement to determine the capacity of the battery or state of charge. 9 10 Ni‐Cad Ni‐Cad It is highly dependent upon such factors as BATTERY CAPACITY length of stand time subsequent to charging, Capacity is a measure of the stored electrical the magnitude of the discharge current, and energy, generally expressed in ampere‐hours, battery temperature. that is available for use from a fully charged Typically, it would be about 1.25 volts when battery. Unless otherwise stated, the rated measured at the 1‐hour rate at 75‐80 degrees capacity refers to that obtained at a 1‐hour F. discharge rate under room temperature conditions. 11 12 2  9/13/2021 Ni‐Cad Ni‐Cad The nominal rating of a nickel‐cadmium As an example, a battery rated at 20 ampere‐ battery generally refers to the number of hours will deliver 20 amperes for a minimum ampere hours that the battery can deliver of 1 hour when discharged to the 1 volt per when discharged at the 1‐hour rate to 1 volt cell endpoint at room temperature. per cell. The 1‐hour rate is that discharge rate expressed in ampere, at which a battery will give up its usable capacity in 1 hour. 13 14 Ni‐cad and constant voltage Ni‐Cad and Constant Voltage Ni‐cads installed in most airplanes are If the start has been difficult, a high current has been subjected to a constant voltage charging taken from the battery for a prolonged period of source, the aircraft generator. These time. The battery, especially the center cells, get warm. generators have a high current producing These cells, being warmer than the other cells, have capability. a lower internal resistance. Turbine starters require a lot of electrical When the engine starts and the generator gets on energy. The battery provides this, and it line, a high current is put back into the battery. usually does it without much strain. 15 16 Ni‐Cad Overhaul Ni‐Cad Overhaul Overhaul of a nickel‐cadmium battery consist If a nickel‐cadmium battery has been serviced of a complete discharge and disassembly. in accordance with the manufacturer's All of the Cells are scrubbed clean and dried recommendations and still does not pass the with hot air. The battery is completely capacity test, it may be possible for the inspected and reassembled, using new battery to be completely overhauled by the separator material.(between cells and case) manufacturer or an approved shop. 17 18 3  9/13/2021 CAPACITY TESTING Connect the battery across a load bank and Discharge the battery: The only way to discharge it at the 1‐hour rate until an average accurately determine the true state of charge of 1 volt per cell is reached. of a nickel‐cadmium battery is to discharge it If the discharge time is less than the time and measure its ampere‐hour capacity. specified by the battery manufacturer, (typically 1 hour), this is an indication that the capacity of the battery has decreased and a further discharge or equalization is required. 19 20 Ni‐Cad Ni‐Cad Charge the battery: Use a constant current Adjust the electrolyte: When the battery is charger or special battery charger/analyzer fully charged, Its electrolyte will be at its and charge the battery at its five hour rate highest level in the cells. Measure the until it reaches the voltage recommended by electrolyte at this time. It should be at the the battery manufacturer. For a typical 19 cell level recommended by the battery battery this would be 30 volts or 1.58 volts per manufacturer. cell. This level is somewhere around 1/4” above the top of the cell plates. 21 22 Ni‐Cad Adjust the electrolyte level as required using only distilled de‐mineralized water. No potassium hydroxide should be added, as only water is lost in the electrolysis which occurs when the battery is fully charged. 24 4  9/13/2021 Ni‐Cad Deep Cycle 1 ohm 5 watts Discharge the battery. As each cell get to 0 (zero) volts short with a wire across the cells two terminals. Allow all of the cells to reach a completely discharged condition. Allow the battery to sit 3 to 8 hours. 25 Ni‐Cad Deep Cycle Ni‐Cad Deep Cycle Recharging: After the rest period, the battery In the last 5 minutes of charge, the voltage of is placed on a constant current charge at its the individual cells are measured. Any cell not five hour rate, for seven hours. having a voltage somewhere between 1.55 This will put 140% of its rated ampere‐hour and 1.80 volts at a temperature between 70 capacity back into and 80 degrees F. is considered faulty and must be replaced. 27 28 Ni‐Cad Ni‐Cad Final Check: Before the battery is returned Any time a battery is serviced a complete to service a final check is made of the torque record should be made of the battery of all the inter‐cell connection hardware, the condition. level of the electrolyte, and leakage current This record will enable you to spot troubles between the cells and the case. before they become serious. 29 30 5  9/13/2021 Ni‐Cad Ni‐Cad Records The record should contain such items as – condition of the case and individual cells Nov 11/14 – tightness and condition of inter‐cell connections. – Electrolyte level and the amount of water added Nov 11/14 to each cell. Feb 10/15 – The voltage of each cell at the end of the charge, May 10/15 Aug 8/15 – and mention hotspots or conditions to note on Nov 10/15 subsequent inspections. 31 Ni‐Cad To determine the approximate state of charge of a nickel‐cadmium battery, discharge it at 0.2C1 amperes for about 10 seconds and then measure the terminal voltage with an accurate voltmeter. If the reading is 1.25 Volts or more per cell, the battery is at least half charged. If the cell voltage is less than 1.25 volts the battery should be recharged. 34 Ni‐Cad Ni‐Cad i.e. 0.2 * C1 Charging at a constant current C1 = battery type 1201 = 12 Ah To charge a completely discharged battery use one of the following procedures. 0.2 * 12 = 2.4 amps – Charge at 0.1 C1 amperes until the battery voltage There for discharge the cell at 2.4 amps for 10 reaches an average of 1.5 volts per cell. seconds and measure the voltage. – Then continue charging at this rate for 4 If the cell voltage is greater than 1.25 volts the additional hours battery is at least 1/2 charged. (The total charge time must be at least 14 hours, but no more than 16 hours.) 35 36 6  9/13/2021 Ni‐Cad Ni‐Cad Cont’d The manufacturer of the SAFT nickel‐cadmium Charge at 0.5 C1 amperes for at least 2 hours. If after this time the battery voltage has not battery suggest that the battery be completely yet reached an average of 1.55 volts/cell disassembled and all their components continue to charge at this current rate until thoroughly inspected and cleaned once a the voltage rises to this level. year. – Do not charge at this rate for more than 2 hours and 30 minutes Then charge at 0.1C1 for 4 more hours. 37 38 Test next week Definitions call it a day – to quit work and go home; to say that a day's work has been completed. “ I'm tired. Let's call it a day.” “ The boss was mad because Tom called it a day at noon and went home.” 7