Car Battery Voltmeter Circuit
The main onjective of the car batter voltmeter circuit using LED is to work as a warning inducator using a voltmeter circuit to test the life of car batteries. A voltmeter, though can be bought from a store, is designed as a circuit to make the whole arrangement a lot more interesting. A voltmeter is basically a testing device that is used to measure the potential difference between two points of either AC or DC form. Here the voltage is measured by associating the voltmeter with the charge left in the battery.
The voltmeter circuit is connected across the battery terminals. That is, the battery voltage is given to the inverting inputs of the IC. The indicated voltage on the voltmeter is compared with the reference voltage which is processed on the zener diode D1. The zener diode works like a usual diode and allows the current to flow in one direction, but also has a characteristic of current flow in the opposite direction if the voltage is more than its breakdown voltage. This obtained value is adequate to supply good thermal stability.
A 10K POT is also connected to change the voltage levels to output in the form of glowing LED’s. The output LED indicators must show car battery voltage with an interval step of 1 Volt (11V, 12V, 13V & 14V).
This is a very useful circuit which when installed on your car gives the voltage of you car battery in a LED dot display form. The circuit is based on four comparators made of quad op amp LM324. The inverting inputs of IC are kept at at reference voltages 5.6V, 5.2V, 4.8V, 4.4V respectively at pins 2, 6, 9, 13 by resistors R3, R4, R5, R6. The battery voltage is directly fed to the pin inverting input through the voltage divider arrangement using R1 and R7. When there is a variation in the input supply the output of each op amp goes high accordingly as they are wired as voltage comparators. Thus the corresponding LED glows.
If a car battery indicates an output voltage of 12 Volts or more, using the voltmeter circuit, it means that the battery has a good life. If the battery voltage goes below 12 Volts and up to 11.6 Volts, it indicates that the battery has started discharging. If the battery voltage goes even lower there are only two possibilities. Either the battery is failing or it is low in water.
It is always advisable to measure the battery charge at “high current” instance. This can be obtained by turning ON the head lamp in high beam mode. While checking the output voltage at this condition, if it shows a steep drop, better change the battery soon.
Voltmeter Circuit Diagram and Parts List
|R3, R4, R5||680 Ohms|
|R8 to R11||1K|
|D1||5.6V / 0.5 Watts Zener Diode|
|D2 to D5||LED|
- IC LM 324 consists of 4 op amps in one package, so power supply is common and is shown once (pin 4 and 11).
- To setup, connect the circuit to battery, adjust R6 so that required voltages are available at the inverting pins (refer description to get the required voltages).
- Fix the LED’s on the dash board and mark the voltages near to it as shown in circuit diagram. The gadget is now ready.
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