Hi all,
I'm looking for a device similar to the BQ33100 but for Automotive application. I'm a student and working on my senior project. We have created our own design and I would love all of your feedback!
Using Serial Communications, (Sent in Binary with serial.write(SERIAL_ARDUINIO)) the master can send a value to a specific chip telling it to turn on, read its supercapacitors voltage, send it back to the master and finally turn back off. This method ensures minimum current draw from cells and eliminates the need for a voltage divider (which is constantly drawing power).
The slaves are isolated from the master by a device called optoisolator. This device transmits incoming serial data digitally by blinking its build in LED. On the opposite side of the isolator, an opto transistor senses the binary data and opens its gate to simulate the flashing LED with serial data. The gate allows current to flow into the receiving pin on the ATtiny841 chip thus transmitting the correct data.
On receiving this "interrupt" signal, the chip will wake, delay, receive the serial communication, check that message with its own value stored in EEPROM. If it matches, a voltage will be read and mapped based on the internal ref voltage. This voltage will then be converted sent back to the master (Serial.write) using an optoisolator like before.
There are additional relays which switch the ground in when measuring a cells voltages. The problem with this is voltage cannot be read when discharging the caps, this might be an issue.
As long as only one chip is sending and receiving data, all chips can be wired in parallel, reducing the number of pins on the master.
Balancing Cells
To balance the caps sells a method commonly used when a large number of small voltage cells are wired in series (Li-ion, supercaps, etc) of "shuttling" energy from a full capacitor to a less full capacitor via a shuttling supercapacitor.
