Multi Battery Charger – WiFi enabled

Overview

This project is about creating a multi battery charger that is smart enabled.  The circuit allows up to 8 batteries to be charged from a single battery charger.  When the battery charger is started, it starts charging one battery at a time, until all batteries have been charged.  At this point, the battery charger will turn off.

Features of the charger

• Multiple batteries can be charged
• Auto turn off when completed
• Automatic changing to next battery when charged
• Capable to handling 30A charge current
• Simple interface
• Voltage/Current display
• Built with ESPHome
• WiFi Enabled – allow to be integrated into Home Assistant
• Bring your own charger – This device just switches between batteries, it is not responsible for the type of battery connected

Components

• 8 Channel WiFi enabled relay board

Inputs / Output

Inputs

• On/Off button
• Start/Pause button
• Next/Stop button
• Current – ADC connection

Outputs

• 8 Relay outputs
• 8 LED’s showing relay status
• Running LED
• Charger relay on/off
• Unit on LED

Connections

• Running LED connected to the Charger relay on/off output
• 8 LED outputs added as an extension on the built in HC595 serial/parallel converter
• Current through the ADC pin
• Unit On LED – on when power to the unit

Pseudo Code

Here is some pseudo code for the battery charger

Variables

• unit_state (default value is on as unit will be on) – states can be on, off, pause, running
• relay_active ( number of the current active relay) – default is 1
• current_countdown – counts down number of below threshold readings – default 3

On/Off Button

• Button press
  • If unit_state is off
    • set unit_state to on
    • Turn on all LEDs for 0.5 second (LED test)
    • Turn on LEDs to show number of active outputs
    • set relay_active=1
  • if unit_state is pause, running, on
    • Turn unit_state to off
    • Turn off all relays
    • Disable relays
    • Turn off charger relay

Start/Pause Button

• Button Press
  • if unit_state is on or pause
    • if unit_state is on, then set relay_active to 1 (reset to start)
    • set unit_state to running
    • Turn off all LEDs
    • Turn on LED for active relay
    • Turn on relay for active LED
    • Enable relays
    • Enable charger relay
  • if unit_state is running
    • Turn off charger relay
    • Turn off active relay
    • Disable relays
    • set unit_state to pause
    • (Leave LED on to show current battery being charged)

Next / Reset Button

• Button Press
  • if the button is pressed less than than 0.5 second (Next)
    • if unit_state is running
      • Turn off battery relay
      • Turn off battery LED
      • Increment relay_active
      • if relay_active > 8, then relay_active=1
      • Turn on battery LED
      • Wait 15 (?) seconds
      • Turn on battery relay
    • If unit_state is paused
      • Turn off battery LED
      • Increment relay_active
      • if relay_active > 8, then relay_active=1
      • Turn on battery LED
  • if button is pressed > 3 seconds (Reset)
    • Turn off battery relay
    • Disable relays
    • Turn off charger
    • set relay_active = 1
    • Turn on LEDs showing active outputs
    • set unit_state = on

Current Sense Reading

Current sense will be read every 15 seconds, and filtered to give an average over 3 readings.

• if reading > minimum threshold
  • current_countdown = 3
• if reading < minimum threshold
  • decrement current_countdown
  • if current_count = 0
    • Turn off battery relay
    • Turn off battery LED
    • Increment relay_active
    • if relay_active > 8,
      • Disable relays
      • Turn off charger
      • Turn off LEDs
      • set relay_active = 1
      • set unit_state to off
    • else
      • Turn on battery LED
      • Wait 15 (?) seconds
      • Turn on battery relay

Pin Outs for the Charger

Relay control

The board comes with an HC595 controlling the relays.  The pin-outs are hard coded.  The following table shows the pins that are used on the ESP32, along with the connections to the chip