## Car Battery Voltmeter Circuit

### Description

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.

NOTE:

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

ComponentSpecification
ICLM324
R115K
R21.2K
R3, R4, R5680 Ohms
R610K POT
R710K
R8 to R111K
D15.6V / 0.5 Watts Zener Diode
D2 to D5LED

### Notes

• 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.

Our website has more related circuits that you may like to read, Take a look:

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1. Ariharan T

But a car battery delivers high current right?. Are u using 1/4 W resistor in this circuit ?

2. i have made this circuit and it works but all 4 leds light at a time please can any one tell me what should be the status of leds on varying voltage .i have used simple 9v battery for it..

• Check orientation of 5.6v zener.
This circuit is powered by the battery ( cars 12v battery ) that it is showing status of. No need for 9v battery

10k ohm pot, R6, should be set to 7480 ohms.

3. Thanks! is a very easy circuit usint also one IC.

4. For your Car Battery Voltmeter Circuit, would you be able to tell me what resistor values I would need to monitor a 6 V supply? I am looking to build a circuit to visually indicate whether a device is receiving 5.7V-6.3V (Indicating all is well), 3V-5.69V(Might be a short) or Below 3V(basically dead).
Matt Bragg

• Charles Tomlinson

Hi Matt, I am not sure exactly what you require but if you change the zener to a lower value, say 2.8v this mite be a good place to start experimemting for you.
Good luck
Chas.

5. Destate9

First of all, it seems unnecessary to use two pins of the pot (R6). Second of all, I understand this circuit must work for you, however, why did you choose for the LEDs to be powered with the unregulated voltage of your car battery when it can sweep from 11-14 volts? Also, R8-R11 are pretty large for your typical LED resistor. Your probably getting 9-12 mA per LED when they can take up to 20 mA

6. excellent circuit,i am serching for this circuit for a long time..thanks

7. How would you change this circuit for voltages less than 4? I teach grade 9 students and a project is a wind turbine. This would be great for them to see some yellow, red and green LEDs

8. tkanks good circuit which i was looking since long.pl keep sending such good circuits for my wv 1958 model .

9. Что-то я почти ничего не понял..