The circuit below will provide you a beeping alarm when your battery is low (below your low battery set point) and also turn off any circuit or device connected to it when battery goes below your second set point.
The beeping circuit consists of two transistor astable multi-vibrator which turns the buzzer on in short pulses avoiding continues high pitch noise.
LOW BATTERY PROTECTION AND ALARM CIRCUIT USING P-MOSFET
The circuit is designed around LM358 operational amplifier configured as comparator (click here to download data sheet). The IC has two different op amps (A and B) in a single package. Both op amps are given a common reference voltage of 4.7V or 5.1V using zener diode D2. Variable resistors U3 and U4 are used to set the operating points (thresholds) of their corresponding op amps.
low battery alarm Setting
When setting low battery alarm, monitor the battery voltage using voltmeter. Now let the battery run down to the point where you always want to be notified and adjust U4 until the buzzer start beeping and LED2 starts blinking.
Setting low battery protection or shutdown
After the alarm, let the battery drain some little more and adjust U3 until the output light and the alarm goes off. These settings are done once and it will always work for u as set.
Please note that, when the system turns off, it may not be able to turn on instantly unless the battery level has increased beyond a certain level which is set by R7. (Hysteresis). This functions sees to it that the circuit does not turn on and off unnecessarily.
To increase the turn off / turn on time, please decrease or increase R7.
The beeping circuit consists of two transistor astable multi-vibrator which turns the buzzer on in short pulses avoiding continues high pitch noise.
Low Battery protection and alarm for Inverters and battery powered applications
LOW BATTERY PROTECTION AND ALARM CIRCUIT USING P-MOSFET
LOW BATTERY PROTECTION AND ALARM CIRCUIT USING RELAY
The circuit is designed around LM358 operational amplifier configured as comparator (click here to download data sheet). The IC has two different op amps (A and B) in a single package. Both op amps are given a common reference voltage of 4.7V or 5.1V using zener diode D2. Variable resistors U3 and U4 are used to set the operating points (thresholds) of their corresponding op amps.
low battery alarm Setting
When setting low battery alarm, monitor the battery voltage using voltmeter. Now let the battery run down to the point where you always want to be notified and adjust U4 until the buzzer start beeping and LED2 starts blinking.
Setting low battery protection or shutdown
After the alarm, let the battery drain some little more and adjust U3 until the output light and the alarm goes off. These settings are done once and it will always work for u as set.
Please note that, when the system turns off, it may not be able to turn on instantly unless the battery level has increased beyond a certain level which is set by R7. (Hysteresis). This functions sees to it that the circuit does not turn on and off unnecessarily.
To increase the turn off / turn on time, please decrease or increase R7.
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