Welcome to the Stoffel Systems Insights video series.
I'm Eric Stoffel, President of Stoffel Systems.
In this series, we'll discuss battery management systems as used in lithium-ion battery packs.
Let's begin with an introduction to what a battery management system, or BMS is.
A BMS has two primary functions when it comes to a battery pack.
Its two primary functions are to keep the battery pack operating safely and keeping it operating reliably.
And if you think about it,
all the advanced features that you can see in a BMS really at its core boil down to one of these two features.
Is it keeping the battery pack safe or is it maintaining reliable operation?
So it's helpful to stay in the context of what the purpose of that feature is.
So let's take a look at a black box model of a battery management system.
So at its core, a battery management system is a system that takes a number of inputs.
So I'll draw a black box here for our BMS.
So for example, it takes in a number of voltages.
For example, every cell voltage and the pack voltage.
It takes in a number of temperature sensors,
typically temperature sensors sprinkled throughout the pack to get a sense of temperature distribution of the cells.
And it also takes as an input the current flowing into or out of the pack.
So for example, is the battery pack charging or discharging and at what magnitude?
And then within the BMS, it's running a number of algorithms to try to generate an accurate estimation of the following outputs.
So one of the primary outputs is what's called the SoC, or state of charge, and this is typically referred to as the fuel gauge.
It's what you see on your phone when it says 75% remaining, or an electric vehicle, 50% remaining.
That's your state of charge.
It's also generating a state of health estimate.
So at a high level, the state of health is how much capacity the battery pack can store relative to what it was when you first got it, or beginning of life.
So for example, if you've had a cell phone for a couple of years, you know that your battery life is not as good as it was originally.
Maybe your state of health is only 70% of what it was when you first got it.
And here at Staffle Systems, we've developed also a safe operating envelope,
which allows you to know how much current you can either charge or discharge at, at any given time.
And finally, the BMS is also outputting a number of faults or status signals that the application controller needs to be aware of.
And so there can be certain conditions where these are triggered.
We'll have a more in-depth video about each of these topics in the future, but at a high level,
the BMS is taking a number of inputs, running a number of algorithms and estimations to generate these outputs to the application system controller.
So what does a BMS look like in a schematic?
So BMSs can be used in single or multi-cell lithium ion battery applications.
For the purposes of this video, we'll talk about multi-cell applications.
So for example, what I've just drawn here, this is a 3S1P battery pack, because it has three cells connected in series.
And the BMS is a circuit board that typically resides very close to the cells that monitors the voltage at each of these points to get a sense of,
to get a measurement of the cell voltage, the individual cell voltages, as well as the BMS is also monitoring the overall pack voltage.
And in addition to that, the BMS is measuring the current flowing into or out of the pack,
either via a shunt current sensor or a Hall effect type current sensor.
And then finally, the BMS has a master disconnect that allows it to terminate charge or discharge of the battery if it detects that a system,
that the battery is entering into an unsafe or undesirable state.
And over here, you have your external terminals that connect your battery pack to the external world.
So for example, this could be a motor controller, an electric vehicle, it could be a solar power inverter.
If you're generating energy from the sun, it could be a DC-DC converter, it could be a charger,
anything that allows you to charge or discharge this battery is on the outside.
So the BMS is able to monitor everything going on internally and communicate that via some sort of interface,
so this is a comms interface, to an outside controller that can use that information to better update its behavior.
So at a high level, this is what a battery management system does, and in future videos e'll go into each of these topics in more detail.
Thanks for watching, see you next time.