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Simple battery charger

Hi everyone,

to charge the 12V - 1,2Ah lead acid battery I found this scheme very simple and unpretentious ... what do you think?

cbat.jpg

with the V1 trimmer I adjusted the charge voltage to 13.7V as indicated on the battery ....

3 questions:

- does the battery have to be disconnected when I adjust the charge voltage?

- the L2 led lights up when the battery is charged or discharged?

- is a 15V power supply for LM317 okay?

thank you.
 

billybob

Active Member
I would check this link. https://circuitdigest.com/calculators/lm317-resistor-voltage-calculator It's just a LM317 calculator.
I think 10k potentiometer is a little much. Max for the potentiometer should be 2400 ohms to get 13.75 volts.
Or just replace R2 with 1K ohm and it should be fine.

I don't think it matters either way to have the battery disconnected or not, might help to be on the safe side though and have a Volt or Amp meter alongside this circuit.

The zener's breakdown is rated for 11 volts that's when the Led will come on.

I believe 15 should be fine, what is the amperage?

There are better circuits out there, but this one will get the job done if the values are correct.

Add a heatsink to the Lm317.
 

audioguru

Well-Known Member
Most Helpful Member
Or just replace R2 with 1K ohm and it should be fine.
No. The value of R2 must be low enough for the LM317 minimum load current which is a max of 10mA. Therefore 1.25V/10mA= 125 ohms, use 120 ohms. The datasheet shows a 240 ohms resistor for the more expensive LM117 that has a minimum load current of 5mA.

I don't think it matters either way to have the battery disconnected or not, might help to be on the safe side though and have a Volt or Amp meter alongside this circuit.
A discharged battery will probably reduce the voltage of this circuit but the circuit has an output diode that does not conduct much without a load.

The zener's breakdown is rated for 11 volts that's when the Led will come on.
No. The 2V LED is in seroes with the 11v zener so the LED will begin to glow at 13.0V.

I believe 15 should be fine.
No. The datasheet for the LM317 says its input must be at least 2V higher than its output. The battery label said charge at 13.7V and there is a diode and resistor at the charger output so the output of the LM317 is 15V then its minimum input must be 17V.
 

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