Auto Off 12V NiCad Battery Charger Circuit

NiCad/NiCad battery charger circuit is still needed since some application demanding high current is still rely on NiCad type, since this type is still superior in term of  high current output (low internal resistance) and low cost. This is the figure of the circuit;

This battery charger circuit is used to charge 12V NiCad battery at  around 74 mA until battery is fully  charged. This circuit need around 4 hours to fully recharge a totally empty/dead battery, depends on the battery capacity. This circuit is basically a current source with auto cut-off. The current regulation is done by maintaining a fix voltage across a 68R at the emitter of  2N2219 transistor. This voltage is stabilized by a 5.6V zener diode 1N752, which keep the voltage at 68R resistor at around 5V, giving a constant current of 74 mA.  The auto-off feature work by monitoring the output voltage (before the 1N4001 diode) relative to ground, as this voltage increases in accordance with the battery voltage which is being charged.  After the battery voltage reach the fully-charged level, the lower 1N752 zener diode will pass the current to activate the 2N222 transistor, which short the upper transistor’s base, turning off the charging process. To calibrate the shut off point, connect a 270 ohm / 2 Watt resistor across the charge terminal and adjust the pot until the charging terminal voltage  show 15.5V level.

Automatic Battery Backup Circuit

This is a design schematic for battery backup circuit. The diode-OR connection is the simplest link between backup battery and a main supply with a load. But, when the battery voltage is greater than main supply voltage, it will not work. To solve this problem we can use the circuit below. This is the figure of the circuit;

This circuit has the backup supply of 9V battery and main switch-mode supply voltage ranges from 7V to 30V. It uses the MAX931 which is an ultra-low-power comparator with a 1.182V band gap reference. When it is used in normal condition, the battery’s negative terminal floats, the three parallel-connected n-channel FETs are off, and the comparator output is low. The n-FETs  will turning on, the negative terminal of the battery will be grounded and the comparator’s output goes high when the main voltage declines to 7.4V.

To eliminate the supply-rail glitch that would otherwise happen when switching from the battery to the main supply, the delay was used. It can be done by using the R6, C1, and D1. An unacceptable reset in the system’s microcontroller can be occurred while the glitches. For proper operation, the value of R3 and R4 should set the hysteresis in the MAX931 to 800mV. [Circuit Source: maxim-ic.com]

Automatic 12V Lead-Acid Battery Charger Circuit

This is design for charger circuit that is suitable for lead-acid battery, including flooded, gel, and AGM types. This circuit is simple design. This is the figure of the circuit.


The automatic term means that this charger will stop charging automatically when the battery voltage reach a certain pint, indicating that the battery has been fully charged, and charging will be restarted if the battery voltage falls below that threshold. A LED indicator is provided to show you when the battery is fully charged. This automatic battery charger can be left connected to a battery indefinitely to maintain full charge safely.

How is the circuit work?
1. R2 is used to adjust the final voltage when the charger should stop charging. For flooded and gel type, the batteries are usually charged to 13.8V. For cycling the battery (AGM or gel), 14.5V to 14.9V is usually recommended by battery manufacturers. Set the R2 pot to midpoint, turn on the charger and connect a battery to its output. Monitor the charge with a voltmeter until the battery reaches the proper end voltage, then adjust the pot until the LED glows constantly. To charge different types of batteries, you can mount the pot on the front of the case and mark each position of every battery types ending voltage.
2. Install proper heat sink for Q1. A small fan might be necessary and can generally be powered right off the output of D1 If the circuit is mounted in a case.
3. Choose T1 transformer which is appropriate for your local line voltage (120V, 220V, etc.) with 12 Volt secondary output.
4. If the circuit is powered off, you should disconnect the battery because the circuit will drain the battery slowly, and this could damage your battery if the battery is drained while it’s voltage falls below about 10V.

Lead Acid Battery Charger Circuit

This is battery charger circuit that is use a fly back converter topology, and implements a current-limited power supply to charge lead-acid batteries. This circuit is control by MAX471 IC. This is the figure of the circuit.


The flyback transformer provide isolation and voltage input range flexibility, event at supply voltage lower that the battery voltage. Monitoring the charging current is done by sensing the output using MAX471 current sense amplifier. The result of the output current monitoring is then used to give a feedback to a threshold detector, to detect if the value falls below the predetermined threshold. This detection is used to switch the charger into trickle mode, when a lower voltage is applied for lower charging current. [Schematic source: Maxim Integrated Products Application Notes]

Battery Charger Circuit Using Ammeter VU

This is a design of the circuit diagram of a simple and straight forward battery charger that can be used to charge all type of 12V rechargeable batteries including car batteries. This circuit is completed with ammeter VU for displaying the current. This is the figure of the circuit.


The circuit is nothing but a 12V DC power supply with an ammeter for monitoring the charging current. The two diodes forms a centre tapped full wave rectifier. The capacitor filters the rectifier output to produce a clean 12V out put. At initial stages of charging the ammeter will read about 1 to 3 amperes. As the battery is slowly charged the current slowly decreases. For indicate when the battery is fully charged, the ammeter reading will be zero. For attention, it is always be careful to connect the charger to the battery in correct polarity. The polarity is connecting between positive to positive and negative to negative.

Simple Car Battery Charger

This is a circuit for battery charger. But the circuit can places in a car. This is a simple design and useful to make it. In this circuit there is facility for monitoring the charging current and voltage. This is the figure of the car battery charger.


The circuit is based on the IC MC78T12ABT from Freescale. The IC is nothing but a 7812 in TO-3 package with 3A capacity. The transformer T1 steps the mains voltage to 15V AC and diodes D1&D2 does the job of rectification. The transformer T1 can be a 230V primary; 15-0-15V, 3A secondary step down transformer. Capacitor C1 does the filtering and C2 acts as a decoupling capacitor. The ground terminal of IC1 is lifted to 2.1V using the diodes D3, D4 and D5. So the output from the IC1 will be a regulated 14.1V (12+2.1).The battery is charged via diode D6.The D6 blocks reverse flow of current from battery to charging circuit when the mains power is not available. Meter M1 shows the charging current and M2 shows the charging voltage. Fuse F1 can be a 1A fuse. The meter M1 can be a 3A ammeter. Meter M2 can be a 20V volt meter.

Cell Lithium Ion Charger Circuit

This circuit was build to charge two series Lithium cells (3.6 volts each, 1 Amp Hour capacity) installed in a portable transistor radio. This operation using LM339 to amp the signal input. The charger will operates by supplying a short current pulse through a series resistor and then monitoring the battery voltage to determine if another pulse is required. The current can be adjusted by changing the series resistor or adjusting the input voltage. When the battery is low, the current pulses are spaced close together so that a somewhat constant current is present. As the batteries reach full charge, the pulses are spaced farther apart and the full charge condition is indicated by the LED blinking at a slower rate. The below figure is about the circuit of the charger.


A TL431, band gap voltage reference (2.5 volts) is used on pin 6 of the comparator so that the comparator output will switch low, triggering the 555 timer when the voltage at pin 7 is less than 2.5 volts. The 555 output turns on the 2 transistors and the batteries charge for about 30 milliseconds. When the charge pulse ends, the battery voltage is measured and divided down by the combination 20K, 8.2K and 620 ohm resistors so that when the battery voltage reaches 8.2 volts, the input at pin 7 of the comparator will rise slightly above 2.5 volts and the circuit will stop charging.

The circuit could be used to charge other types of batteries such as Ni-Cad, Ni-Mh or lead acid, but the shut-off voltage will need to be adjusted by changing the 8.2K and 620 ohm resistors so that the input to the comparator remains at 2.5 volts when the terminal battery voltage is reached. Be careful not to overcharge the batteries. I would recommend using a large capacitor in place of the battery to test the circuit and verify it shuts off at the correct voltage.

Battery Discharge Monitor Using TL431

This is a battery monitor circuit which disconnect the load when the battery is discharged, preventing a deep discharge which could cause permanent battery damage. The battery is automatically reconnected when a battery charger or other DC source is connected across the load. Select a relay which requires less than 100ma coil current and with contacts capable of handling the load and charging currents. This figure is about the circuit.


The principle work of the circuit is C1 should be about one hundred micro-farads and C2 may be near 1 micro-farad. C2 simply delays the closing of the relay long enough for C1 to charge and C1 keeps the relay closed long enough for the battery voltage to climb above the cut-off point (about 22 volts for the circuit as shown). The 210k resistor may be reduced to 92k for 12 volt batteries. These R1 values may be reduced if a lower drop-out voltage is desired. The circuit may cycle on and off several times if the battery is deeply discharged with a delay proportional to the value of C1. The load sees the full voltage of the charger before the relay connects the battery in this circuit and in some applications the version below may be more desirable.

Simple Ni-Cad Battery Charger

This simple charger circuit uses a single transistor as a constant current source. The voltage across the pair of 1N4148 diodes biases the base of the BD140 medium power transistor. The base-emitter voltage of the transistor and the forward voltage drop across the diodes are relatively stable. The charging current is approximately 15mA or 45mA with the switch closed. This suits most 1.5V and 9V rechargeable batteries.


The principle work of the charger is between one batteries with other battery dissociated by packer wall which there is in battery box, mean every space at battery doesn't correlate in consequence electrolyte fluid at every battery nor correlates (partition wall between batteries there shall no which leak).

In one batteries there is arrangement of plate that is some plates for positive pole (between plates dissociated by timber, ebonite or plastics, depends on technology applied) and some plates for negativity pole. Active agent from positive plate made from chocolate tin oxide (PbO2) while active agent from negativity plate is tin (Lead) pore (like sponge). The plates soaked by electrolyte fluid that is sulfate acid (H2SO4).

Automatic Batteray Charger

This circuit basically is consisted of a comparator, that monitors reference tension which permanent. If battery tension exceeds maximum level which has in determining before all, relay would be active and will stop charging current. If battery tension went down under its low threshold value, relay is discharged causing enables reenter charging current.


Comparator formed by operation amplifier IC 741. Power allowance tension for amplifier Opamp stabilized by R8 and D4, so that is not influenced by stress variation of battery. Reference tension for operational amplifier alighted from power allowance is stabilized this through R7 and D3. Reference tension compared to a part of battery tension, what taken away from voltage divider R9/R10/R11.

For tuning of tension at R10 enters don’t tumble operational amplifier will become height, makes Q1 and Q2 on, causing activates relay and breaks current pegisian to battery. This aflame LED indicates that battery has been full loaded. To prevent battery connected returns to admission filling if there is the voltage drop a few, hence some of output tensions of operation amplifier is baited to input don’t tumble through R5 and R6. So thereby the operational amplifier is functioning equal to schmitt.