Battery Level Automatic Load Shutdown for 24V inverter System

The aim of this project is to design an inverter battery monitor and low battery load level shutdown with the following specifications:

- LED Display

- Adjustable maximum voltage level

- Adjustable minimum voltage level

- 3 Adjustable alarms (typically 50%, 30%, 20%)

- Alarms to be non-irritating, and have a mute function

- Minimum buttons

- Low power consumption

For my design, I opted for the AtMega328P micro. 

The LED display was designed to be simple and easy to interpret. There are 6 LEDs, indicating the voltage level in a LED BAR method:

Led 6 - 100%

Led 5 - 80%

Led 4 - 60%

Led 3 - 40%

Led 2 - 20%

Led 1 - 0%

The 0% Led is to be linked to the programmed minimum voltage level

The 100% Led is to be linked to the programmed maximum voltage level.

The scaling between 0% and 100% is linear. For 0%, only Led 1 will be on, and for 100%, all LEDs will be on.

For power saving, the LED display does not stay on. To turn on the display, a button needs to be pressed, and the display will turn off after 30 seconds.

To be able to measure the voltage, the battery voltage needs to be down scaled. Using a resistor divider, the voltage is scaled down to 1.1V with a 1M and 82K resistor. With the A/D converter set to the internal 1.1V reference, this means that the maximum measureable voltage will be around 14.45V, high enough for the design.

There are 5 voltage levels that needs to be monitored:

- maximum voltage level

- minimum voltage level

- alarm 1 voltage level

- alarm 2 voltage level

- alarm 3 voltage level

Instead of using trimpots, I decided to go for a more unconventional way. Via a programming procedure, apply the specific voltage levels in turn, and save the various A/D results in EEPROM.

The LEDs are used to indicate the programming sequence, and the same button used for the display, is used for programming.

A normal piezo buzzer is used for the alarm. as this should be load enough. Provision for three alarms were made, with the following properties:

- Alarm 1, to beep once every few seconds. Should be able to silence this alarm

- Alarm 2, to beep twice every few seconds. Should be able to silence this alarm

- Alarm 3, to beep three times every few seconds. This alarm can not be silenced.

Once an alarm is silenced, I needed an automatic reset function to enable the alarms again if the battery has been charged. I included a reset function that will enable all alarms again if the battery voltage exceeds 60% again.

To silence the alarms, the same button used for the display is used.

I tested these alarm sounds in my house, without any complaints from my wife and son, so I am sure it will not be irritating in the outdoors world.

You will need a variable power supply and a multi meter to calibrate the unit.

Entering Calibration Mode

- Press and hold the button

- Connect unit to power supply

- After 5 seconds, the unit will beep continuously

- Release the button

- Unit will give 6 beeps (setting maximum voltage)

- Top LED will be on

- Uit is now in CALIBRATE mode. To exit this mode, remove power from the unit without pressing the button.

- Adjust power supply output to the maximum voltage to be displayed on the LED display (typical 12.7V)

- Press the button

- Unit will give 5 beeps (setting minimum voltage)

- Bottom LED will be on

- Adjust power supply output to the minimum voltage to be displayed on the LED display (typical 11.8V)

- Press the button

- Unit will give 4 beeps (setting Alarm 1)

- Bottom 4 LEDs will be on

- Adjust power supply output to Alarm 1 voltage level (typical 12.4V)

- Press the button

- Unit will give 3 beeps (setting Alarm 2)

- Bottom 3 LEDs will be on

- Adjust power supply output to Alarm 2 voltage level (typical 12.2V)

- Press the button

- Unit will give 2 beeps (setting Alarm 3)

- Bottom 2 LEDs will be on

- Adjust power supply output to Alarm 3 voltage level (typical 12.0V)

- Press the button

- Unit will give 1 long beep to indicate end of calibration, and LED display will turn on for 30 seconds.

All programming values are stored in EEPROM, so the unit only needs to be calibrated once.

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ADMINENGR ABIOLA JOHNSON OPEYEMI

abiola.johnson@outlook.com

theyoungengineerzz@gmail.com

WhatsApp +234-8079593532

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