Simple Battery Charger For Mini Inverter

Simple Battery Charger For Mini Inverter

Introduction

Here is the circuit diagram of a simple and straight forward 12 V battery charger circuit with diagram. This circuit can be used to charge all type of 12V rechargeable batteries including car batteries.

Let's start by understanding few basic things about a Lead acid battery so that we can build our charger more efficiently. Most of the lead acid batteries in the market are 12V batteries. The Ah (Ampere hours) of each battery may vary based on the required capacity, a 7 Ah battery for example will be able to provide 1 Amps for a duration of 7 hours (1 Amps *7 hours = 7 Ah). Now after complete discharge the battery percentage should be around 10.5, this is the time for us to charge our batteries. The charging current of a battery is recommended to be 1/10th of the Ah rating of the battery. So for a 7 Ah battery the charging current should be around 0.7 Amps. Current greater than this may harm the battery resulting in reduced battery life.

Circuit diagram(Simple Battery Charger For Mini Inverter)

Simple Battery Charger For Mini Inverter

Components required

• SCR 1 – 2N6397 – 1no
• SCR 2 – 2N5060 – 1no
• Diode– 1N5402 – 4nos
• Diode– 1N4002 –1no
• Zener diode – IN4736 – 1no
• Resistor – 2k – 2nos
• Resistor– 1.5k – 1no
• Resistor– 10k – 1no
• Resistor – 560ohm – 1no
• Variable resistor – 10k – 1no
• Capacitor – 100uf/25v – 1no
• LED – green 5mm – 1no
• LED – red 5mm – 1no
• Transformer – 220v-15v,3a,150VA – 1no

How circuit works

Charging part

To begin with, an AC220V will flow to a transformer to transform to 15 volts.  Then, flow to bridge diode to rectifier AC to DC pulse 15V. The LED1 is a power indicator of the circuit.

Beginning SCR1 is working. Because the 15V flow to R3, to limit the current to decrease and flow through to diode D5.

It protects the reverse voltage before bias to Gate of SCR1.

When SCR1 conducts, make the 15V flows through cathode to positive battery terminal.

Ideally, SCR1 will conduct current and stop current alternately very fast with a frequency of 100 Hz.

Since the 15V voltage from the bridge diode is full wave rectifier. So the output frequency of 50Hz+50 Hz. The current of this feature is a continuous positive half of the sine wave.

Which it is different from the voltage with capacitor filter, that is smooth as a straight line.

So SCR1 does not conduct the current all time. When there is positive voltage to bias at Gate.

Since the waveform of voltage is DC pulse, not smooth.

The SCR will stop conducting current. If disconnecting is not a positive voltage.

Then, the positive voltage waveform comes to SCR1 again. It will start conduct currents again, this was reversed with a frequency 100 Hz.

Auto cut off part

The positive battery voltage flows through R2 to reduce current. And, C1 will filter a current to smooth.

Second, the current flows through VR1 to divide voltage down. Then,  the Zener diode-ZD1 pass an overvoltage to bias lead G of SCR2.

We adjust a level of VR1 to set a full battery.  Until voltage at negative of ZD1  is more than 6.8V or about 7.3V.

After that, ZD1 is saturation voltage collapse flow through to feed Gate of SCR2.  It causes SCR2 to conducts current.  By R4 is a helper to SCR2 extraordinary stable work.

When SCR2 work, causes a negative voltage flows to lead Cathod to Anode. It results to LED2 glow.

And the same time SCR1 will stop conducting current.

Since Gate of SCR1 get negative voltage from SCR2 there. In the case of battery is lower voltage, causes the voltage at negative of ZD1 is lower than 6.8V.

It makes Gate of SCR2 does not get positive voltage. But it can get only negative voltage through R4, result SCR2 does not conduct current.

Calibration of the circuit

The best way to calibrate the circuit is to use a variable voltage, regulated power supply. This is connected to the circuit in the place of the battery. Set the regulated power supply to 14.5 volts or fully charged battery and adjust the VR1 to a point where the LED2 ON.