12v Led Battery Level Indicator Circuit (Led Bar Graph)

Most often, I come across many situations where I needed a lead acid battery voltage level monitoring circuit. Here is an example; I use lead acid battery for my inverter and so it requires constant voltage charging. But inverter provides current charging only, so I use a self-made battery charger circuit which provides a constant 14 volt charging. Charger output should be maintained at 14 volt; else it will reduce the battery life.This made me think of building a battery voltage monitor circuit one for myself, and here is my circuit design. It can indicate voltages using Led’s in levels of 8 with variable sensitivity. You can use this led level indicator for monitoring battery voltage.
The heart of this monitor is a LM324 IC. You can also use LM3914 IC also to get 10 levels from single IC but it’s comparatively expensive.

Components Required:

  1. LM 324 IC X 2
  2. LED X 8
  3. Resistor (1K X 17)
  4. Potentiometer(1K X2)

Battery monitor circuit diagram

                                                     Click on the image for enlarged view

Working of voltage detector

  • Battery level comparison is done using LM324 IC which has 4 in-built comparators. Here we are using two IC’s to get 8 levels.
  • To each comparator’s inverting (negative) terminal, we are giving a reference voltage by using voltage divider resistors.
  • Positive of all the comparators are shorted and connected to the positive terminal of the battery which is to be monitored.
  • If the voltage of the battery is higher than the reference level of each comparator, then the output of corresponding comparator will be high. Then the Led will glow.
  • AT the output you can connect LED,s or barcode displays to increase good-looking.
  • Here the LEDs glow in a bar graph display manner, if you want each Led’s to glow independently to indicate each level; you can connect a priority encoder ic 74147 and 74138 decoder IC.
  • Sensitivity of this voltage tracker can be adjusted by varying the potentiometer.
  • In case you want to control the charger circuit at a particular level, you can connect a relay at the output of respective comparator. For this you will have to use switching transistors (Refer transistor switching for inductive loads). We will discuss this in another post in details.

Pin Out

2 thoughts on “12v Led Battery Level Indicator Circuit (Led Bar Graph)

  1. What about reference voltage?! If battery level indicator is to know when to change the old battery it does not make sense to use a reference voltage for voltage dividing operation.I am finding one of such circuits for my project to know when to change the battery if voltages are below critical level. So can u give any explanation or replacement circuit about this reference voltage…

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