When several batteries have to be charged from the same power supply, charging them all at once can exceed the available current. You need chargers that can agree with each other: each one looks after its own battery, but only one charger at a time actually charges.
That is why we developed the firmware and electronics of a smart charger: each charger is a small node built on the ESP32-C3 with the TI BQ25887 charger, and all the nodes form a radio network with no central unit.
In short: switch on the chargers, connect the batteries and the system organises itself. No communication wiring between stations and no central controller to configure.
Texas Instruments' BQ25887 is a charger for 2-cell series Li-ion batteries that runs from a 5 V USB input and steps the voltage up with a boost converter. It has built-in cell balancing, so both cells stay at the same voltage and the battery lasts longer.
The chargers communicate over ESP-NOW, Espressif's radio protocol that links ESP32 devices directly, with no router. Every few seconds each node sends a heartbeat with its battery voltage and state, and keeps a table of the other chargers around it.
Using that information, each node decides on its own with a state machine:
At power-up it listens to the network to see whether anyone is already charging.
The battery needs charging: it waits until the slot is free.
Nobody else is charging: it enables the charger and tells the network.
Battery full or out of range: the charger stays off.
If two chargers are ready at the same moment, the same one always wins based on its address, so there are no conflicts. If a node is switched off, the others notice within seconds and the slot passes to the next one.
Every charger has a built-in web page. At power-up it opens a Wi-Fi network for one minute: connect with your phone and the dashboard opens by itself, with no app to install.
RISC-V microcontroller with Wi-Fi and the ESP-NOW radio, programmed in C++.
EspressifBoost charger from 5 V USB for 2 cells, with cell balancing and a built-in ADC.
Li-ion 2SRadio network with no master: periodic heartbeats and a table of nearby chargers.
Peer-to-peerAccess point and captive portal: the dashboard opens from your phone, no app.
Wi-FiFirmware and web pages updated from the server, with every file verified.
SHA-256Constant firmware supervision and automatic restart if it hangs.
ReliabilityWe design firmware and electronics for chargers, battery management and connected devices. Tell us about your project.