This battery level indicator offers (5) LEDs that light up progressively as the voltage increases. This is a variation of the following 12V Battery Level Indicator and is a great DIY project. http://www.electroschematics.com/6868/12v-battery-level-indicator-circuit/
|LED Color||Charge Level|
|Red||Power Connected (0%)|
|Orange||Greater than 21V (25%)|
|Yellow||Greater than 23V (50%)|
|Green||Greater than 25V (75%)|
|Blue||Greater than 27V (100%)|
|Blue||full charge is about 28 to 29V|
Of course, you may select your own colors if desired.
Bill of Materials
D1 is the voltage reference zener. Tied to this is a string of divider resistors (R2-6) that set the various fixed voltage levels. R7 & 8 form a voltage divider to that divides the battery voltage by a factor of 6. U1 is an LM339 quad comparator that compares the various voltages from the two dividers. The comparator sections have open collector outputs that simply function as switches to operate the LEDs. D7 protects against reverse battery connection.
The LM324 op amp should work OK, but the pin-out is different—and (4) LM741 op amps should also work OK.
It worked as expected and when R2 is calibrated properly, the voltage thresholds are within about 0.1V of stated values. There is no hysteresis so the LEDs tend to flicker slightly at the threshold voltages—this is not a problem.
The LEDs are biased to operate at about 1mA which is reasonably bright if high efficiency LEDs are used—mine were not of the high efficiency type. This current can be adjusted simply by varying the series resistors (R9 through R13). The overall current drain as shown is about 12mA with all the LEDs illuminated. To reduce power, a push-to-test pushbutton is recommended.
Battery Level Indicator Photos
The LEDs are old design — not too bright, but the photo does not do justice. I did not have an yellow LED and the orange LED appeared red.