battery charge monitor circuit diagram

Hi,

This is the circuit diagram of a 3 LED bar graph type battery monitor circuit that is ideal for monitoring the voltage level of an automobile battery.When battery voltage is 11.5V or less transistor Q1 will be On and the LED D1 will be glowing.When battery voltage is between 11.5 and 13.5V, the transistor Q2 will be On and the LED D2 will be glowing.When battery voltage is above 13.5V the transistor Q3 will be On and the LED D7 will be glowing. HOW THIS WORKS?.

The rightmost 2/5 of this circuit could operate independently from the left 3/5.
Furthermore the left 3/5 could be divided into two portions.

The multiple diode strings are a handy technique to fine-tune the zener value.

Tell you what...

Here is a simulation. It was snapped just at the point where the upper 2 led's are lit. (I believe the green led should indicate normal operation. The yellow led should indicate overcharge.)



Of course it would assist understanding if you can see it in animation.
Fortunately this simulator has the ability to export a link which contains the entire simulation.

Click the link below and it will open the falstad.com/circuit website, load my schematic, and run it on your computer.

https://tinyurl.com/ajplsz2

The animated simulation shows when current starts to flow in which wires, and when it stops.

Move the slider at the right, and you will see what volt levels cause the led's to light up and go dim.

You can change values at will. Right-click on a component, and select Edit.