Parameters of batteries
- 1. S.Gomathy M.E.,M.B.A Parameters of Batteries S.Gomathy Assistant Professor Department of EEE Kongu Engineering College
- 2. S.Gomathy M.E.,M.B.A The characteristics of batteries are defined by a set of battery parameters. These parameters include charge storage capacity, terminal voltage, rate at which batteries can be charged and discharged, the cost of battery, the number of times the charging-discharging cycle can be carried out in a battery lifetime and so on. Ideally, we would like our battery to work for many years and should give us required energy in all conditions. Based on the parameter values mentioned by the manufacturer, the selection of a battery can be made.
- 3. S.Gomathy M.E.,M.B.A The standard parameters of a battery specified by the manufacturers are following: Battery terminal voltage (in volts), Charge storage capacity (in Coulomb or ampere-hour or Ah), Depth of discharge (in percentage), Number of useful charging-discharging cycle (in number), Life cycle (in years), Self discharge (in %), etc.
- 4. S.Gomathy M.E.,M.B.A Battery Terminal Voltage (V) The electrical energy transfer from battery to load is possible only when there is voltage difference between two terminals. A battery’s terminal voltage is the voltage difference between its two electrodes. The voltage difference between the battery terminals is driving force for current to flow. For solar PV system applications, there are batteries which are available with 6 V and 12 V ratings. Each battery is made up of cells. The terminal voltage of cells is determined by the material they are made up of.
- 5. S.Gomathy M.E.,M.B.A Normally, the cell voltage is not large to give us required 6 V or 12 V Therefore, many cells are connected together in series to get higher voltage. In a 12 V Lead-acid batteries, 6 cells are connected together. The battery terminal voltage changes with the condition of battery. The terminal voltage increases when battery gets charged, the terminal voltage decreases when battery gets discharged.
- 6. S.Gomathy M.E.,M.B.A Battery Open Circuit Voltage and Terminal Voltage The terminal voltage of battery is maximum when it is fully charged and when no current is flowing. The condition of no current flow is equivalent to open circuit. The maximum terminal voltage of battery is also referred as open circuit voltage of battery or Vo. When current flows through battery, its terminal voltage is normally lower than the open circuit voltage, Vo. This happens because of the internal resistance of the battery. Due to its own resistance, some voltage drop occurs inside the battery. This voltage drop is equal to the current flowing through the battery multiplied by the internal resistance of the battery or equal to I × Ri
- 8. S.Gomathy M.E.,M.B.A The battery has its internal resistance due to many factors. The factors like the contacts within the cells, metal plates/electrodes and salt bridge/separator, even the electrolyte creates some internal resistance. Open circuit voltage of a battery is higher than the terminal voltage under usage due to internal resistance of batteries.
- 9. S.Gomathy M.E.,M.B.A Terminologies for Battery Terminal Voltage Open circuit voltage: It is also called theoretical voltage because this is the maximum possible voltage at output terminals of battery when circuit is open. Nominal terminal voltage or operating voltage: It is actual voltage available at the output terminals of the battery on which load can operate. The standard battery nominal voltages available are 1.5 V, 3 V, 6 V, 12 V, 24 V, 48 V, etc. Cut-off voltage: It is a voltage up to which the load can be operated and below which the battery should be disconnected from the load in order to prevent it from over-discharge.
- 11. S.Gomathy M.E.,M.B.A Battery Storage Capacity (C) The capacity of a battery is the capacity to store the charge in the battery. It is the product of current (in amperes) it can deliver for a given time (in hours), i.e., Ampere × Hour (Ah). One ampere-hour (Ah) is the amount of charge delivered when constant current of one ampere (A) is used for one hour (h). The capacity of non-rechargeable batteries normally varies in few mAh(milli Ah) to several Ah range. The capacity of rechargeable batteries can vary from few Ah to thousands of Ah.
- 12. S.Gomathy M.E.,M.B.A The capacity of batteries depends on temperature. The same battery will have different capacity at different temperatures. The capacity is specified at standard test conditions of 25 °C. Hence, the capacity value measured at installation sites may vary from the values given by the manufacturer because of the change in temperature at particular location. Therefore, while selecting the battery for a given purpose, temperature of the location should be taken in account.