A charge controller circuit for battery makes you hassle-free by not bothering about switching the charger with different battery levels, the main advantages being improved life and low current consumption as it switches off the charger when battery full charged. So far we have published a simple battery charge controller circuit using 555 IC where many of our readers commented that it was difficult for them to set the threshold levels and also it seemed like it was harder to analyze working of the same.
For the above reasons, I have decided to introduce another one where you could find it easier to set the threshold levels. Furthermore, this charge controller design makes it easier for debugging. The main component of this circuit is a LM324 comparator IC which has four inbuilt comparators inside; here we are making use of only one. You can use any other comparator ICs instead of this one, like LM358, LM317, LM339 etc. I have used lm324 here owing to its high availability. For basic electronics learners see what is a comparator.
As the threshold levels to turn ON and turn OFF the charger are different (hysteresis), it helps to avoid oscillation problems of the relay due to leakage current of battery. The threshold levels can be set by varying the potentiometer. As we are switching the charger with the help of relays, you can connect any capacity battery. High current transformers are recommended when using higher capacity batteries to decrease the charging time. For small capacity batteries you should use a series resistance to limit the charging current and that’s not necessary for higher capacity batteries.
This charging controller circuit can be applied with any system that makes use of rechargeable batteries like emergency, UPS, inverters, telephone receivers etc. Here we have used LEDs to indicate the charging status. Also at the bottom I have uploaded a video demonstration to guarantee you that this charge controller schematic is 100% working.
Click on the image for enlarged view
- LM324 IC
- Zener diode 5.1V
- Bridge IC/1N4007X4
- Diode 1N4007
- Transistor BC548X2
- Led Green
- Capacitor 1000uF
- Resistor 1KX4, 100K
- Pot 50K/47K
- Relay 12V/10A
- Transformer 0-15V/2A
- Step down transformer steps down the line voltage to 15 volts and bridge rectifier does the AC to DC conversion process (rectification), it’s followed by the capacitor filter which removes AC ripples.
- The power supply for the working of charger circuit is given from the battery (as it should always be monitoring the battery voltage level even when the mains supply is disconnected).
- The non-inverting terminal of the comparator is connected to a zener diode and 1k resistor which are used to make a reference voltage of 5.1 volt, and its inverting terminal is used to monitor the battery level.
- Usage of zener diode instead of resistors makes sure that the reference value is independent of battery level and temperature variances.
- In fact the comparison is not between reference voltage and the actual battery voltage, but between a proportional value of battery level and reference value. This proportional value is achieved by using a potentiometer.
- If the battery level is below the Lower Threshold Point (say LTP), then the reference voltage becomes higher than the proportional battery value. Thus output of comparator becomes positive.
- Then the transistor is switched ON (as output of comparator is connected to the base of transistor BC548 through a 1k resistor) followed by the relay. I have used a freewheeling diode along with the relay to de-energize the inductor.
- And when the comparison goes reverse, output of comparator is low and transistors are OFF resulting in the disconnection of supply.
- Output of comparator is also connected to another BC548 through a 1k resistor which make hysteresis. That means when the charger is ON, transistor is ON and it makes a 100k resistor parallel with the respective voltage divider, then the drop across the divider will again decrease increasing the charging level.
- Upper Threshold Point (voltage level when charger is switched OFF) can be set by varying the potentiometer.
- The difference between UTP and LTP (hysteresis) can be varied by changing the 100k resistor, decreasing the resistance increases the hysteresis and vice versa.
- A 8.2ohm 10 watt resistor connected in series with the circuit helps to limit the charging current. It’s not required for higher capacity batteries as the charging time will increase.
That’s all! Let me know through the comments box below if something confuses you.