Simple but reliable car battery tester


Posted on Feb 4, 2014

This circuit uses the popular and easy to find LM3914 IC. This IC is very simple to drive, needs no voltage regulators (it has a built in voltage regulator) and can be powered from almost every source. When the test button is pressed, the Car battery voltage is feed into a high impedance voltage divider. His purpose is to divide 12V to 1, 25V (or l


Simple but reliable car battery tester
Click here to download the full size of the above Circuit.

ower values to lower values). This solution is better than letting the internal voltage regulator set the 12V sample voltage to be feed into the internal voltage divider simply because it cannot regulate 12V when the voltage drops lower (linear regulators only step down). Simply wiring with no adjust, the regulator provides stable 1, 25V which is fed into the precision internal resistor cascade to generate sample voltages for the internal comparators. Anyway the default setting let you to measure voltages between 8 and 12V but you can measure even from 0V to 12V setting the offset trimmer to 0 (but i think that under 9 volt your car would not start). There is a smoothing capacitor (4700uF 16V) it is used to adsorb EMF noise produced from the ignition coil if you are measuring the battery during the engine working. Diesel engines would not need it, but i`m not sure. If you like more a point graph rather than a bar graph simply disconnect pin 9 on the IC (MODE) from power. The calculations are simple (default)




Leave Comment

characters left:

Related Circuits

  • New Circuits

    .

     


    Popular Circuits

    Sequential flasher
    Telephone blinker
    Preprogrammed single-chip microcontroller
    Temperature-to-frequency converter
    Fast-overvoltage-protector
    Bedini Motors
    Touch Switch Monostable/Timer with 555 IC
    build varying brightness ac lamp circuit
    Dodd Station
    The beginning and end of a three-phase motor winding speed judgment circuit



    Top