This is the circuit diagram of battery charger which has many important features such as current-constant charging, overcharge protection, short-circuit protection, deep discharge protection and more. The constant-current charging is a popular method for lead-acid and Ni-Cd batteries. In this circuit, the battery is charged with a constant current that is generally one-tenth (1/10) of the battery capacity in ampere-hours. So for a 4.5Ah battery, constant charging current would be 450 mA.

D1 is a low-forward-drop schottky diode SB560 having peak reverse voltage (PRV) of 60V at 5A or a 1N5822 diode having 40V PRV at 3A. Normally, the minimum DC source voltage should be “D1 drop+Full charged battery voltage+VDSS+ R2 drop,” which is approximately “Full charged battery voltage+5V.” For example, if we take full-charge voltage as 14V for a 12V battery, the source voltage should be14+5=19V.

How this battery charger circuit works:

To make the simple explanation, lets divide this battery charger circuit into three sections: constant current source, overcharge protection and deep-discharge protection sections.

Constant Current Source

The constant-current source is built around MOSFET T5, transistor T1, diodes D1 and D2, resistors R1, R2, R10 and R11, and potmeter VR1. Diode D2 is a low-temperature-coefficient, highly stable reference diode LM236-5. LM336-5 can also be used with reduced operating temperature range of 0 to +70?C. Gate-source voltage (VGS) of T5 is set by adjusting VR1 slightly above 4V. By setting VGS, charging current can be fixed depending on the battery capacity. First, decide the charging current (one-tenth of the battery”s Ah capacity) and then calculate the nearest standard value of R2 as follows:
R2 = 0.7/Safe fault current.

R2 and T1 limit the charging current if something fails or battery terminals get short-circuited accidentally. To set a charging current, while a multimeter is connected in series with the battery and source supply is present, adjust potmeter VR1 slowly until the charging current reaches its needed value.

Overcharge Protection

Overcharge and deep-discharge protection have been shown in dotted areas of the circuit diagram. All parts in these areas are subjected to a maximum of the battery voltage and not the DC source voltage. This makes the circuit work under a wide range of source voltages and without any influence from the charging current value. Set overcharge and deep-discharge voltage of the battery using potensiometers VR1 and VR2 before charging the battery.

Deep-Discharge Protection

In overcharge protection, zener diode ZD1 starts conducting after its breakdown voltage is reached, for example, it conducts when the battery voltage goes beyond a prefixed high level. Adjust the variable resistor VR2 when the battery is fully charged (say, 13.5V in case of a 12V battery) so that VGS of T5 is set to zero and hence charging current stops flowing to the battery. LED1 glows to indicate that the battery is fully charged. When LED1 glows, the internal LED of the optocoupler also glows and the internal transistor conducts. As a result, gate-source voltage (VGS) of MOSFET T5 becomes zero and charging stops.

Normally, zener diode ZD2 conducts to drive transistor T3 into conduction and thus make transistor T4 cut-off. If the battery terminal voltage drops to, say, 11V in case of a 12V battery, adjust the potensiometer VR3 such that transistor T3 is cut-off and T4 conducts. LED2 will glow to show you that the battery voltage is in low condition.

Values of zener diodes ZD1 and ZD2 will be the same for 6V, 9V and 12V batteries. For other voltages, you need to suitably change the values of ZD1 and ZD2. Charging current provided by this circuit is 1 mA to 1 A, and no heat-sink is required for T5. If the maximum charging current required is 5A, put another LM236-5 in series with diode D2, change the value of R11 to 1 kilo-ohm, replace D1 with two SB560 devices in parallel and provide a good heat-sink for MOSFET T1. TO-220 package of IRF540 can handle up to 50W.

Built this battery charger circuit on a general-purpose PCB and enclose in general box / cabinet after setting the charging current, overcharge voltage and deep-discharge voltage. Mount the potensiometers VR1, VR2 and VR3 on the front panel of the box.

This battery charger circuit has the following features:

1. It can charge 6V, 9V and 12V batteries. Batteries rated at other voltages can be charged by changing the values of zener diodes ZD1 and ZD2.
2. DC source voltage (VCC) ranges from 9V to 24V.
3. The charger is short-circuit protected.
4. Constant current can be set as per the battery capacity by using a potmeter and multimeter in series with the battery.
5. Once the battery is fully charged, it will attain certain voltage level (e.g.13.5-14.2V in the case of a 12V battery), give indication and the charger will switch off automatically. You need not remove the battery from the circuit.
6. If the battery is discharged below a limit, it will give deep-discharge indication.
7. Quiescent current is less than 5 mA and mostly due to zeners.

EFYmag

This is the circuit diagram of rechargable battery charger which use solar cell / photovoltaic as the DC source. This circuit works to charge 3 types of rechargable batteries that are lead acid, Ni-Cd and Li-ion. The lead-acid batteries are generally utilized in emergency lamps and UPS. The photovoltaic module or solar cell explained in this post is capable of producing a power of 5 watts. At full sunlight, the solar cell outputs 16.5V. It can deliver a current of 300-350 mA.

How the circuit works?

The working of the circuit is quite simple. The output of the solar panel is fed via diode 1N5402 (D1), which acts as a polarity guard and protects the solar panel. An ammeter is connected in series between diode D1 and fuse to measure the current flowing during charging of the batteries. As shown in Image #1, we have used an analogue multimeter in 500mA range. Diode D2 is used for protection against reverse polarity in case of wrong connection of the lead-acid battery. When you connect wrong polarity, the fuse will blow up.

For charging a lead-acid battery, shift switch S1 to “on” position and use connector “A.” After you connect the battery, charging starts from the solar panel via diode D1, multimeter and fuse. Note that pulsating DC is the best for charging lead-acid batteries. If you use this circuit for charging a lead-acid battery, replace it with a normal pulsating DC charger once a week. Keep checking the water level of the leadacid battery. Pure DC voltage normally leads to deposition of sulphur on the plates of lead-acid batteries.

For charging Ni-Cd cells, shift switches S1 and S3 to “on” position and use connector “B.” Regulator IC 7806 (IC1) is wired as a constantcurrent source and its output is taken from the middle terminal (normally grounded). Using this circuit, a constant current goes to Ni-Cd cell for charging. A total of four 1.2V cells are used here. Resistor R2 limits the charging current.

For charging Li-ion battery (used in mobile phones), shift switches S1 and S2 to “on” position and use connector “C.” Regulator IC 7805 (IC2) provides 5V for charging the Li-ion battery. Using this circuit, you can charge a 3.6V Li-ion cell very easily. Resistor R3 limits the charging current. Image #2 shows the circuit for a small LED-based lamp. It is simple and lowcost. Six 10mm white LEDs (LED2 through LED7) are used here. Just connect them in parallel and drive directly by a 3.6V DC source. You can use either pencil-type Ni-Cd batteries or rechargeable batteries as the power source.

Assemble the circuit on a general purpose PCB and enclose in a small box. Mount RCA socket on the front panel of the box and wire RCA plug with cable for connecting the battery and LED based lamp to the charger.

With this circuit, you can save on your electricity bills by switching to alternative sources of power.

Schematic diagram:

The charge will start if a battery is connected between pins JP1-JP4 or JP2-JP4 or JP3-JP4. For example, if a battery is connected to JP1-JP4 pins then the current that flows cause a voltage drop to R1, then D1 causes a voltage drop of 0,7 volts and ?1 conducts. Then through transistor’s emitter flows a current that comes from Adjustment pin of LM317.

NiCd – NiMH Battery Charger Circuit Notes:

• I is 1/10 of the battery’s charging capacity. For example if battery has a rated capacity of 1700mA then ?=170.
• Diode D4 prevents current to flow from battery back to the charging circuit. Resistors R1,R2 and R3 adjusts the charging current and it’s value is given from : Rx=(1,25 + 0,1) / I , where x = 1,2,3.
• The input voltage must be at least 3 times the battery’s voltage. For example an input voltage of 25V can charge a 8,4V (9V) battery.
• R3 is 1/2 Watt and R1 and R2 it’s 1/4 Watt.
• Pins distribution:

PCB top and bottom layout: