project is automatic while others are manual in process. It means that someone needs to trigger the “ON” button or switch to start the irrigation process. In this project, the section
was being improved by placing a component called timer. The function of timer is to run the irrigation process automatically. As a result, the cost of employee will be reducing
because the all the irrigation process is automatic and no need an extra employee to run the irrigation process.
2.4 Charge Controller
The main function of charge controller is to control the rate of rechargeable battery charging process. It is also known as charge regulator or battery regulator. It will prevent
overcharging and may prevent against overvoltage, which can reduce the battery lifespan and performance. Electronic circuitry in regulator measures battery voltage, which rise as
the battery state-of-charge increase. At some voltage which is different depends on the types of batteries at different temperature, the regulator in charge controller circuit will
limit the charging process to the battery. Charge controller circuits are used for rechargeable electronic devices such as cell phones, laptop computers, portable audio
players, and uninterruptible power supplies, as well as for larger battery systems found in electric vehicles. Figure 2.2 below shows the charge controller circuit that will be use in
this project. The circuit was being modified by increase the load dump resistor value up to 20ohm 20W to meet the requirement of the current rating of circuit which is 1A. The dump
load resistor 68ohm 3W rating only suitable for the low current application.
Solar power is routed from the PV panel through the 1N5818 Schottky diode to the battery. When the battery reaches the full setpoint, the output on the lower half of the
TLC2272 dual op-amp turns on. This activates the IRFD110 MOSFET transistor and connects the 15ohm 20W dump load resistor to the battery. The load across the battery
causes the battery voltage to drop, and the comparator circuit turns back off. This oscillation continues while solar power is available. The 300nF capacitor across the op-
amp slows the oscillation frequency down to a few hertz. The two 100K resistors in series provide a regulated 4.5V reference point for use as comparator reference points.
Figure 2.2: 12V 1A Charge Controller Circuit
The 2N3906 transistor is wired with a zener diode in its base circuit, when the PV voltage is above 12V; the 2N3906 transistor turns on and enables the comparator circuit.
The upper half of the TLC2272 op-amp inverts the dump load control signal, this is used to power the high intensity red LED. The LED turns on when the battery reaches the full
setpoint. The LED does not waste any useful charging power since it only turns on when the battery is full. The 78L09 IC provides 9V regulated power to the comparator circuitry.
Operational power for this circuit is provided entirely from the PV panel, so there is virtually no power taken from the battery at night.
It is necessary to match the load resistor to the output of the power source. The 68 ohm resistor shown in the schematic is a good match for a 200mA PV panel. To tune the
circuit for a 1A PV panel, the dump resistor should be able to handle 1A at the battery full voltage. A 13 ohm 20W resistor would be a practical value to use; so in this project, a 15
ohm 20W resistor been use to meet this requirement. If the load resistor is connected directly across the PV panel at noon on a cool and sunny day, the resistor value should be
set so that the PV output voltage drops to just below the batterys desired full voltage.
2.5 Rechargeable Battery
