12v Automatic Charger (Auto Cut OFF)





Introduction: 12v Automatic Charger (Auto Cut OFF)

what is auto cut off battery charger?

some off charger maybe can't stop charging when the battery is fully charged.

Step 1: Circuit

so we want to show you a simple circuit for the charger when the battery is fully charged, the charging automatically stopping,

this is a circuit of the auto cut off battery charger, it has only:-

- one NPN transistor such as c1815 for controlling the charging,

- relay for cutting off this current path through the battery after fully charged,

- 10 kilo-ohm variable resistor connected to the base of the transistor,

the variable resistor used for restricting the voltage from how many volts you want to stop charging!

Step 2: Print

We prepared this circuit for you,

you can download it from the link below

12v Automatic Charger (Auto Cut OFF)

then print it by any printer,

and use any prototyping electronic circuit after that stick the paper to the board,

Step 3: Video

you can see this video and make step by step with this video



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3 Questions

is it applicable to any kind of power source, eg. solar charger or alternator?

Ok. Porém os LED'S não estão invertidos no circuito?

Okay. But the LED's are not inverted in the circuit?

Как будет выглядеть схема на четырех выводной реле?

Что ты имел в виду? Я не понял?


It is very nice idea and good working circuit, but I am not very sure, if it is good for charging battery?.
There are 2 problems. The small one, Led diodes could not light. The big problem is voltage detected by transistor. It is not a battery voltage! (Battery voltage should be increased and should initiate cut off function.) If charger is using constant current, battery voltage is the same like battery, but after cut off, voltage of charger depends on its electric properties and could be different like battery voltage. In some cases can recycle charging.

it's not bad for (10A - 15A ) charger but it's not very smart, known that if the charger connecting to the battery both battery and charger have the same voltage so its no problem if the transistor voltage gives from the charger. at first when you charge the battery the voltage path through the relay if a battery is fully charged not charging else charging it until fully charged.

if you want to make a smart charger you can use LM324 and regulate the voltage at 13.7v for large current and 14,4v for normal current.