Sunday, January 16, 2011

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Car Battery Voltage Indicator

Connecting this circuit to the battery of your vehicle, you will always know at a glance the approximate voltage available. An indication of battery voltage is useful to the motorist for monitoring the battery's capacity to deliver current, and as a check on the efficiency of the dynamo or alternator.

Threshold voltages of the LEDs are set by means of two Zener Diodes (D6 & D10) plus two further Diodes wired in series (D4, D5 and D8, D9 respectively) adding a step of about 1.3V to the nominal Zener voltage.

Car Battery Voltage Indicator Circuit
  • Red LED (D1) is on when battery voltage is 11.5V or less.
  • Amber LED (D2) is on when battery voltage is comprised in the 11.5 - 13.5V range. This indicates that the battery is good if the car  is off. When car is running, this indicates no charge from dynamo or alternator.
  • Green LED D7 is on when battery voltage is 13.5V or more. This indicates a normal condition when car is running and dynamo or alternator are charging.
List Componet Of Car Battery Voltage Indicator Circuit

R1,R3,R6    : 1K   1/4W Resistors
R2 : 100K 1/4W Resistor
R4,R5,R7,R8 : 3K3 1/4W Resistors
D1 : Red LED
D2 : Amber LED
D3,D4,D5 : 1N4148 150mA Diodes
D6 : BZX79C10 10V 500mW Zener Diode
D7 : Green LED
D8,D9 : 1N4148 150mA Diodes
D10 : BZX79C12 12V 500mW Zener Diode
Q1,Q2 : BC547 NPN Transistors
Q3 : BC557 PNP Transistor 

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