Battery life has always been a critical consideration for most of the electronic gadgets and equipment. When we talk about spy cameras, which normally function round-the-clock, they often run out of power within a few days. Many spy cameras (CCTV cameras) are powered by 9V PP3 type batteries that offer five times more energy than the regular 9V alkaline battery.
Mini CCTV cameras also accept 6-12V DC supply from AC mains adaptor through the DC IN jack. AC mains adaptor for the camera increases the capacity of the 9V PP3 battery but is bulky and noisy. Whether disposable or rechargeable batteries, making frequent replacement or recharging them is a cumbersome job. The unique solar power box described here serves an alternative solution to the problem.
Circuit diagram :
The circuit of the solar power box is simple. It contains a battery charger and a battery health indicator and a few other components. As shown in the circuit, DC supply available from the solar panel (SP1) is directly applied to the in-put of the circuit through a protection diode (D1). This diode is used to pre-vent the reverse current flow from the battery to the solar panel during night. Thus, D1 allows the current to flow from the solar panel to the battery only. Low-voltage-drop type 1N5817 diode is perfect for the job.
At the heart of the circuit is an integrated current source, realised using a popular 3-pin adjustable voltage regulator LM317T(IC1). This IC is designed to adjust its internal resistance between the In (pin 3) and Out (pin 2) terminals to maintain a constant voltage of 1.25V between the Out (pin 2) and Adj (pin 1) terminals. Here, a 9V, 280 mAh rechargeable PP3 type Ni-MH battery (BATT) is used as reservoir. Normally, a charging current of about 10 per cent of ampere-hour rating is safe for the battery. Resistor R1 (39-ohm, 0.5W), connected between pin 1 and 3 of IC1, limits the charging current to about 30 mA. DC output from the battery is available at output jack J2. Red LED ( LED1) is used as a battery ‘health’ indicator. Switch S1 is used to start the charging while S2 is used for connect-ing the load. Note that suitable heat sink should be used for the IC1.
The proper selection of solar panel is important but not critical. A miniature 12V type solar panel with a cur-rent output of about 100 mA can be used. Even if you have a solar panel with higher voltage rating, it will not create a problem as the circuit ensures that the charging current cannot exceed the predetermined value.
The circuit can be easily assembled on a general-purpose PCB and housed in a small plastic cabinet.
Author : T.K. Hareendran – Copyright : EFY