AMS: Keeping our Batteries safe

Over the past couple months, we’ve been doing research into the different options we have for the Accumulator Management System (AMS). We got into contact with Linear Technology a while back and it turned out that they’re one of Formula Hybrid’s sponsors. Luckily they were able to provide us with a demo system to evaluate their battery management solutions, sending us some boards based around their battery monitoring IC, the LTC6804-2.

We’ve been playing with the demo system over the past couple weeks, checking to see if everything seems to be working. We initially had to simulate some cells using resistors, since our cells hadn’t been delivered yet:

Simulating cells using a power supply and resistors
Simulating cells using a power supply and resistors

Luckily, our battery cells arrived right before our winter break, so we were finally able to test the demo system using the actual cells. Each board can monitor up to 12 cells, but for testing purposes we’re only using 2 cells each, check out the set-up:

IMAG1212
The whole setup: Cells connect to the boards, each board then sends voltage information to the microcontroller, and ultimately the computer

Here’s a closer look at the PCBs:

Linduino One: The Microcontroller, which acts like an Arduino Uno plus some extras
Linduino One: The Microcontroller, which acts like an Arduino Uno plus some extras
DC1942C: This is the board that takes voltage readings from the cells, it has the LTC6804 on it
DC1942C: This is the board that takes voltage readings from the cells, it has the LTC6804 on it
DC1941C, This is an isoSPI Master so that all our boards can talk to the microcontroller
DC1941C, This is an isoSPI Master so that all our boards can talk to the microcontroller

The demo system let us check if the hardware works as expected, including a GUI so that we could see everything that’s going on. It lets us see the charge in each cell, and includes options to set our Over and Under Voltage limits. It also lets us discharge cells for cell balancing purposes. Here’s a screenshot of the GUI:

LTC6804-2 GUI: You Can see it reports the cells that aren't connected as "UnderVoltage", makes sense since nothing is plugged in!
LTC6804-2 GUI: You Can see it reports the cells that aren’t connected as “UnderVoltage”, makes sense since nothing is plugged in!

Everything seems to be working on the hardware side of things, the GUI and some voltmeters helped us determine that quickly. Information is sent as expected, meaning the boards we received weren’t a dud. The next step, in the software, is proving to be pretty challenging. We have to program the boards to independently behave as we want; a lot of coding is goes into this. We’re looking at sample code from Linear Technology for some insight. More updates to come!

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