Battery Voltage Indicator Circuit
Description
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.
Circuit diagram:
Parts:
- R1 = 1k
- R2 = 100K
- R3 = 1k
- R4 = 3.3K
- R5 = 3.3K
- R6 = 1k
- R7 = 3.3K
- R8 = 3.3K
- Q1 = BC547
- Q2 = BC547
- Q3 = BC557
- D1 = Red Led
- D2 = Amber Led
- D3 = 1N4148
- D4 = 1N4148
- D5 = 1N4148
- D6 = BZX79C10
- D7 = Green Led
- D8 = 1N4148
- D9 = 1N4148
- D10 = BZX79C12
Notes:
- Red LED D1 is on when battery voltage is 11.5V or less. This indicates a low battery charge.
- 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 motor is off. When motor 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 motor is running and dynamo or alternator is charging.