2.5 Rechargeable Battery
Rechargeable battery also known as a storage battery is a group of one or more secondary cells. Rechargeable batteries use electrochemical reactions that are electrically
reversible. Rechargeable batteries come in many different sizes and use different combinations of chemicals. A charge controller circuit needed to control the charging and
discharging process of rechargeable battery. Figure 2.3 shows the graphical picture of charging and discharging process. During charging, the positive active material is oxidized,
producing electrons, and the negative material is reduced, consuming electrons. These electrons constitute the current flow in the external circuit. The electrolyte may serve as a
simple buffer for ion flow between the electrodes, as in lithium-ion and nickel-cadmium cells, or it may be an active participant in the electrochemical reaction, as in lead-acid cells.
Figure 2.3: Charging and Discharging Process
There are several types of rechargeable battery like Nickel-Metal Hydride Battery NiMH, Nickel Cadmium Battery NiCd, Lithium-ion Battery, Lithium sulfur battery,
Thin film battery and Carbon foam-based lead acid battery. Figure 2.4 show the example of the rechargeable battery that been use in completing this project.
Figure 2.4: A 12V Rechargeable Battery
2.6 Timer
A timer is a specialized type of clock. A timer can be used to control the sequence of an event or process. It works reverse in direction compared to the stopwatch. Whereas a
stopwatch counts upwards from zero for measuring elapsed time, a timer counts down from a specified time interval, like an hourglass. Timers can be mechanical, electromechanical,
electronic quartz, or even software as most computers include digital timers of one kind or another. In this project, the mechanical or electronic timer probably uses to complete
this circuit. The timer has a control relay or contactor build in it. Control relay or contactor is an electromechanical device which activates one or more switches according to the
current through a coil not connected to the switches. A relay is essentially an electromagnet with two possible states arranged so that when there is sufficient current the core of the
relays coil attracts a ferromagnetic armature which mechanically operates switches; a spring holds the armature away from the core when not actuated. The spring is designed to
snap the contacts between two stable mechanical states; there should not be a range of coil current which allows the contacts to be in an intermediate state.
2.7 Inverter