Battery Management Systems (BMS) in Lithium Leisure Batteries

The Battery Management System, otherwise known as a BMS, is the ‘intelligent’ component responsible for the management and control of your lithium leisure battery.

This electronic marvel is responsible for keeping yourself and your battery in tip-top condition, through controlling the charge and discharge process of the battery. Although very rare with lithium batteries, if anything were to go wrong during these processes, the BMS would quickly identify the fault, and cut off the power to prevent any potential issues.

Your LiFePO4 cells have a safe and specified range for voltage, temperature, current, discharge and cell balancing. It is the job of the BMS to monitor the battery and ensure the cells remain within the pre-ordained safety parameters.

Do all leisure batteries have a BMS?

It may surprise you to know that not all types of leisure batteries come with a built-in BMS. Despite the obvious safety benefits that come from using a BMS, many lead acid batteries do not utilise BMS technology to monitor battery health.
Up until this point, lead acid batteries have provided a low cost, low cycle power provision, so much so, consumers have been happy working on a ‘throw away’ mentality when it comes to leisure batteries.

However, with the tides now turning, environmental factors playing a huge part in purchasing decisions and costs becoming even more important - the need to look after your batteries is more important than ever. A good BMS connected to your lithium leisure battery can help you do this.

How does a BMS prevent damage to your lithium leisure battery?

The BMS doesn’t just act as a safety net, it also ensures that all individual cells are operating cohesively within your lithium leisure battery. It offers a great way of protecting your leisure battery from issues such as over-discharge, temperature instability, cell and current imbalances. Let’s have a look at these factors in a little more depth;


Over-discharge
Over-discharge protection simply means that when a certain charge (voltage) is reached, the BMS will forbid the cells from discharging any further. If your cells are discharged below a certain level, they can become damaged beyond repair. This feature prevents this from happening.

Temperature Instability
LiFePO4 cells are particularly sensitive to temperature, so monitoring individual cells for temperature instability is of particular importance. If any of the cells are overheating, the BMS will shut down the battery to prevent it from any damage.

Cell Imbalances
Keeping your battery in top condition means keeping all of your cells equally charged and maintained, this prevents any damage to the cells and ensures there is no uneven discharge taking place.

Current Imbalances
Very similar to the over-discharge protection, your BMS also protects against disproportionate charge and discharge currents.

By drawing critical information from each cell, your BMS can help you optimise the performance of your whole battery, giving you overall parameters such as State of Health (SOH) and State of Charge (SOC) - ensuring you get many years of use out of your battery.

What types of BMS are there?

BMS come in all different sizes and shapes, and are designed to work with all different types of battery set-ups.

If you’re planning on building your own system using LiFePO4 cells, you’ll find a wide range of amperes and voltages available to suit your project, although here at Fogstar Drift we mainly stock 12V, 24V, 48V units ranging between 100A and 300A.

When you start shopping around, you’ll notice some BMS (see the JBD BMS) simply look like an open circuit board complete with the associated cables, bolts and Bluetooth connectors. Whereas some BMS are presented in dustproof, shockproof, and in some instances waterproof casing.

What does 4S, 8S or 16S mean in BMS terms?

When shopping around for a BMS to facilitate your LiFePO4 cells, you may see the terms ‘4S’, ‘8S’ or '16S' banded around, and if you’re new to the world of BMS - you may be wondering what this means.

The term ‘4S’ simply stands for ‘4 in series’ - four 3.2V LiFePO4 cells achieving a nominal voltage of 12.8V. The same applies for an ‘8S’ system, ‘8S’ simply stands for ‘8 in series’, or ‘16S’ for ‘16 in series’.

This number (4S/8S/16S) also reflects the quantity of ‘sampling wires’ that come with your BMS. The sampling wire is simply the wire that connects your BMS with each cell - you need to ensure that you have the correct BMS for the number of cells in your series. In some cases, this may require multiple BMS’s!

Can I just use any BMS?

It is critical that when working with Lithium Iron Phosphate cells that you opt for a BMS that is specially designed to work with these specific cells. LiFePO4 cells are remarkably sensitive to over-discharge and overcharging, so the voltage profile of the BMS is designed to account for this additional sensitivity.

If you’re purchasing a BMS directly from Fogstar Drift or Fogstar Batteries, you’ll notice both the JBD and JK BMS come with Bluetooth allowing you to hook your BMS up to the associated Apps.

If you've purchased a Fogstar Drift Lithium Leisure Battery, you’ll notice all of our lithium leisure batteries come with a built in BMS. We also provide a Bluetooth interface, enabling you to connect the BMS to our App. It’s a very simple integration and is designed to be very user friendly.

The Fogstar Drift App allows you to manage all of your battery vitals from any location. You’ll be able to see individual cell data, as well as the overall health of the battery.

So, there we have it. A short introduction into Battery Management Systems. We’ve covered what they are, how they’re used and what the benefits of using them are. The great news is, if you’ve purchased a Fogstar Drift Lithium Leisure Battery, you won’t need to worry about purchasing and installing a BMS - we’ve done the hard work for you!