As per manufacturer’s data sheets, a 12V rechargeable lead-acid battery should be operated within 10.1V and 13.8V. When the battery charges higher than 13.8V it is said to be overcharged, and when it discharges below 10.1V it can be deeply discharged. A single event of overcharge or deep discharge can bring down the charge-holding capacity of a battery by 15 to 20 per cent.

It is therefore necessary for all concerned to monitor the charge level of their batteries continuously. But, in practice, many of the battery users are unable to do so because of non-availability of reasonably-priced monitoring equipment. The circuit idea presented here will fill this void by providing a circuit for monitoring the charge level of lead-acid batteries continuously. The circuit possesses two vital features:

• First, it reduces the requirement of human attention by about 85 per cent.
• Second, it is a highly accurate and sophisticated method.

### Schematic of Lead acid battery charge monitor circuit

The circuit is powered by the battery under test, via a voltage regulator IC. The circuit takes about 100 mA for its operation.
For calibrating the upper and lower reference levels, a digital multimeter and a variable regulated power supply source are required. For calibrating the lower reference voltage, follow the steps given below:

• Set the output of power supply source to 10.1V.
• Connect the power supply source in place of the battery.
• Now the display will show some reading. At this point vary preset VR2 until the reading on the display just changes from 1 to 0.

The higher reference voltage is calibrated similarly by setting the power supply to 13.8V and varying preset VR1 until reading on the display just changes from 8 to 9.
After the calibration is completed, the circuit may be housed in a suitable enclosure. The cost of all the components, including the enclosure, would be around Rs 200.

## Related Tutorials

Hello. What is the wattage of the input resistors?

• hari Krishna

The led lids up with 2 to 3 volt and need a current 20, all you have to calculate the resistor value be referred input volt
Ex. If you are using 10 then 10 multiplied by input current of led as you know approx. 10 ma means .01 A and you will got the required resistance which is 0.1 kohms means 100 ohms..

• B S Murty

A very useful circuit especially nowadays when 12 V Lead Acid Batteries are used frequently in homes etc. Careful monitoring will reduce costs of replacement.

A very useful circuit especially nowadays when 12 V lead acid batteries are used frequently in homes. Regular monitoring will reduce costs of replacement.

• shivanand m b

vry good project for umderstanding thank you efy

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