Home / Circuits / Battery related / 3 Auto Shut off Battery Charger circuits (12V)
Why is an auto shut off battery charger needed?
The main reason to get an auto shut off battery charger is to protect the battery from overcharging and consequently reducing its useful life.
Can a car battery be overcharged?
Yes, you can overcharge a car battery. Car batteries take whatever voltage is sent to them, regardless of whether they are already fully charged. That’s why it’s up to your car’s alternator to send the correct voltage to the battery.
Overcharging a car battery can reduce battery life. But battery overcharging is not common and only happens due to problems that can arise while charging the battery.
What can cause an overcharged car battery?
– Defective alternator: If the voltage regulator is not working properly, it can send a higher voltage to the battery, which can overcharge the car battery.
– Slow chargers left unattended: Trickle chargers deliver a small amount of current to the car battery and allow it to slowly charge over time. If left unattended, slow chargers can overcharge the battery by charging above 12.6 volts.
How to know when the battery is fully charged?
Some battery chargers automatically shut off, other chargers require you to periodically check the charger dial to make sure you are not overcharging the battery.
A car battery is really just a big 12 volt battery. This means that if the car battery is fully charged, it should read a little over 12 volts (12.6) with the car off. While the car is running you should get a higher voltage reading which should be in the 13.6 to 14.6 volt range.
The following auto shut-off battery charger circuits stop charging the battery after the battery has been fully charged.
12V auto shut off battery charger with Current Limiter
This battery charger with current limiter will stop charging the battery when it has 14 volts and limits the charging current to 2 Amps.
12V auto shut off battery charger with thyristor
This battery charger automatically disconnects from mains to stop charging when the battery is fully charged. It serves to charge the battery of our car, using the 120/240 VAC (alternating current).
12V auto shut off battery charger with op-amp & voltage regulator
This battery charger circuit allows you to charge a 12-volt car battery (lead acid battery) using a LM350 voltage regulator and an operational amplifier.