Battery and Charger Circuits


Circuit Project: 3V Low Battery Voltage Flasher

Many battery powered devices use two AA alkaline cells. Often you will not know when it is time to replace the batteries until the device powered by them actually stops operating. The hobby circuit below can be connected to a 3v battery, to give you some warning when the battery is nearing its end of […]


NiCd Battery Charger

The design of the charger is similar to that of many commercially available chargers. The charger consists of a mains adaptor, two resistors and a light-emitting diode (LED). In practical use, this kind of charger is perfectly all right. Resistor R1 serves two functions: it establishes the correct charging current and it drops sufficient voltage […]


Mobile Phone Battery Charger

Small and portable unit, Can be assembled on veroboard Mobile phone chargers available in the market are quite expensive. The circuit presented here comes as a low-cost alternative to charge mobile telephones/battery packs with a rating of 7.2 volts, such as Nokia 6110/6150. Circuit Diagram Mobile Phone Battery Charger Circuit Diagram Parts R1 = 1K […]


Simple NiCd Battery Charger

A simple NiCd charger can be built using ‘junk box’ components and an inexpensive LM317 or 78xx voltage regulator. Using a current limiter composed of R3 and a transistor, it can charge as many cells as desired until a ‘fully charged’ voltage determined by the voltage regulator is reached, and it indicates whether it is […]


Car Battery Voltmeter Circuit

The circuit was developed to create a voltmeter that will be used to test car batteries while showing an indication using LEDs. Voltmeter – a device or an instrument used for measuring the electrical potential difference between two points of either alternating current or direct current electric circuit. LM324 – has internal frequency compensated for […]


12V Lead Acid Battery Desulphator

Lead acid batteries often fail prematurely due to over-charging, under-charging, deep discharging and low electrolyte level. All of these can lead to sulphation of the plates which leads to high internal resistance and eventual failure. Normally, this process is regarded as irreversible but this circuit is claimed to reverse the process by applying high voltage […]


Car Charger for 12V Batteries

The circuit has been designed to produce a battery charger for automobiles that are using 12V batteries only. BTY79 – a 10A Silicon controlled rectifier with an operational temperature range from 0ºC to 125ºC C106D – a 4A sensitive gate Silicon controlled rectifier that functions as reverse blocking thyristors designed for high volume consumer applications […]


Battery Circuit for Backup and Standby Operation

The circuit was designed to create a spare and reserve power source with the use of batteries during the absence of power from the mains. BD139 – NPN power transistor used for driver stages in hi-fi amplifiers and television circuits because of its low voltage at 80 V maximum and high current at 1.5 A […]


Low-Power Car/Bike USB Charger

Looking for an efficient USB charger that can operate from a 12V car battery? This unit functions at up to 89% efficiency and can charge USB devices at currents up to 525mA. Best of all, it won’t flatten the battery if it’s left permanently connected, as long as you remember to unplug the USB device. […]


Low Battery Indicator I

Here is the circuit diagram of low battery indicator from silicon chip electronics. This simple circuit lights LED1 when the battery voltage drops below the setting set by trimpot VR1. In effect, VR1 and associated resistors bias Q1 on which holds Q2 and the LED off. When the voltage drops below the set value, Q1 […]