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Smart Lead-Acid Battery Charger

I did not make it yet

This project is under planning and I have to acquire enough knowledge to build this.


  • Understand procedures to follow when charging lead-acid batteries.
  • Acquire knowledge to build SMPS.



This will convert main supply to suitable voltage level for charging battery and working of microcontroller and other circuits in the system.

It is supposed to have output voltage around 14.2V, which is suitable for charging 12V Lead-acid batteries.

DC-DC Converter

Output voltage from main AC-DC SMPS will be around 14.2V, which needs to be stepped down efficiently to supply for microcontroller based circuit. This circuit should do that. It can be a buck converter followed by a linear voltage regulator. It can step down 14.2V to around 6.5, then a linear voltage regular to convert it to smooth and stable 5V.


It is a circuit that mainly helps to set charging voltage for the battery per control signals from microcontroller.

Microcontroller Based Charge Controller

Of course, it is brain of this system. It will decide charging and stop charing as required.

It is supposed to have following settings (through toggle switches) to control the way of charing the battery:

  • Normal - Float Charge
    • In normal mode, battery is to be charged with voltage 2.30 to 2.45V per cell.
    • In float mode, battery is to be charged with voltage 2.25V to 2.27V per cell.


  • Arduino analyzing the battery while charging and acting accordingly.
  • Need to watch over battery voltage level.

Control Flow

  1. Device turned on. In this situation, Charger will be off and providing no voltage in its output.
  2. Microcontroller get turned ON.
  3. Microcontroller checks open voltage of battery and do actions depending on that value.
    1. Voltage is between 8V and 15V
      1. Set number of cells as 6
      2. Voltage is equal or above to 14.4
        1. Assumes 12V battery, show "Fully Charged" message.
      3. Voltage is between 13.8 and 14.4
        1. If charging mode is set to normal. Then charge battery with 2.30V to 2.45V per cell.
        2. If charging mode is set to float. Then charge battery with 2.25V to 2.27V per cell.
    2. Ensure battery is connected, otherwise show "Battery not connected"
    3. If battery voltage level is below 14, then
      1. Turn on charge for X minutes
      2. Go level up one, on completing charge time.
    4. If battery voltage level is 14 or above, then
      1. Show "Battery charged"


12V to 14.2V Converter Based on UC3843

Maximum output current = 4

Calculation Results

Maximum switching current = 7.1 A

Inductance = 9.8 uH

Resistor Divider For Feedback

  • R1 = 24k
  • R2 = 4.7k
  • Trim pot = 1k