Charge controllers
- 1. S.Gomathy M.E.,M.B.A Charge Controllers S.Gomathy M.E.,M.B.A Assistant Professor Department of EEE Kongu Engineering College
- 2. S.Gomathy M.E.,M.B.A Function of a Charge Controller Charge controllers - control the flow of charge from the battery and to the battery. They protect the battery by preventing over-charge or deep discharge of batteries to preserve their life and performance. When the battery gets overcharged by solar PV module, a charge controller will cut it off from the circuit so that no more charging is possible. Similarly, if a battery goes into deep discharge (or overdischarge) due to excessive use of batteries by the load, a charge controller detects and disconnects the battery from the circuit so that no current can be drawn from the battery. In this way, a charge controller protects the battery. Note that both overcharge and deep discharge conditions damage batteries. Both the situations result in decrease in the life of batteries.
- 3. S.Gomathy M.E.,M.B.A Working of Charge Controller The status of over-charge and deep discharge is detected by measuring the voltage level of batteries. In overcharge condition, the battery voltage increases beyond a certain level and in deep discharge condition, the battery voltage decreases below a certain level. In overcharge and deep discharge voltage conditions, the charge controller disconnects the battery. When the battery voltage level reaches within the normal operating level, the battery gets connected to the circuit. In case of over-charge, battery gets cut-off due to high voltage of battery.
- 4. S.Gomathy M.E.,M.B.A After high voltage cut-off, if the battery is used by load which means some discharge of battery, then its terminal voltage will fall. The charge controller will detect this and connect the battery again for charging Similarly, in the case of deep discharge, the battery gets cut-off due to low voltage of battery. Now, if the battery is under charging condition, its terminal voltage will increase after sometime due to charging. The charge controller will detect the increase in voltage and when voltage increases above the low voltage cut-off level, the charge controller will connect the battery to the circuit so that power can be extracted from the battery by the load.
- 5. S.Gomathy M.E.,M.B.A Types of Charge Controllers The following two types of charge controllers are mostly used nowadays: 1. Pulse Width Modulation (PWM) charge controller or standard charge controller 2. Maximum Power Point Tracking (MPPT) charge controller.
- 6. S.Gomathy M.E.,M.B.A • PWM charge controllers have same nominal voltage across battery bank and PV array. • MPPT charge controllers can have different voltages across battery bank and PV array and operate at the maximum power point tracking (MPPT) of the PV panel. • MPPT charge controller allows us to have a solar panel array with a much higher voltage than your battery bank voltage. • For the same power flow, when voltage is high, current that will flow in the wires is small. • Power is equal to current multiplied by voltage. • Normally, it is desired to keep the current flow to small level. • Therefore, a big advantage of having a higher voltage solar panel array is that we can use smaller gauge wiring to the charge controller, and the use of small gauge wire reduces the wiring cost.
- 7. S.Gomathy M.E.,M.B.A Features of Charge Controller • Nominal system voltage: This is the voltage at which battery and charge controller operate in a PV system. • Nominal load current: This is the maximum load current that charge controller should be able to handle. • Nominal PV array current: This is the maximum PV array current that charge controller should be able to handle. This is nothing but the Array short circuit current. A safety factor of 1.25 is used to account for variation in Short circuit current at non STC.
- 8. S.Gomathy M.E.,M.B.A Charge regulator set points: Charge controllers regulate the charging and discharging of a battery. Charge controller senses the voltage of the battery (or ‘state of charge’, SoC) and decides either to disconnect it from the source (PV array in this case) to prevent it from overcharging or to disconnect the load (from the battery output) to prevent deep discharging. Such controllers are mainly used where loads are unpredictable and the batteries are optimized or undersized to minimize the initial cost. The charge control algorithm has set points (threshold values) depending upon which it takes decisions
- 9. S.Gomathy M.E.,M.B.A Voltage regulation set point (VR): It is the maximum voltage up to which battery can be charged (without getting overcharged). If this threshold is reached, the controller either disconnects the battery from the source or starts regulating the current delivered to the battery.
- 10. S.Gomathy M.E.,M.B.A Voltage regulation hysteresis (VRH): It is the difference between VR and the voltage at which the controller reconnects the battery to the PV source and starts charging. If VRH is too small, it will result in tighter voltage regulation but the control will be oscillatory and may deteriorate the battery life. At the same time, a large value of VRH may lead to ‘slight’ overcharging of the battery during every cycle. VRH also determines how effectively the controller can charge the battery. Low voltage disconnect (LVD): It is the minimum voltage up to which the battery can be allowed to discharge, without getting deep discharged. It is also defined as the maximum depth of discharge (DoD) of the battery. The charge controller disconnects the load from the battery terminals as soon as the battery voltage touches LVD, to prevent it from overdischarging.
- 11. S.Gomathy M.E.,M.B.A Low voltage disconnect hysteresis (LVDH): It is the difference between LVD value and the battery voltage at which the load can be reconnected to the battery terminals. LVDH is not kept too small, or else the load will be switched on and off more frequently which can adversely affect the battery and the load.
- 12. S.Gomathy M.E.,M.B.A Typical Specifications of PWM Charge Controller • Charge controllers are available for various ratings of Nominal system voltage and PV array current. • Typical ratings of 12 V, 6 A rated PWM charge controller are shown in Table.
- 13. S.Gomathy M.E.,M.B.A • An example datasheet 4.5 A, 12 V rated charge controller from morning Star Corporation