Lithium battery management systems

Using Battery Management Systems

All (professional) lithium batteries will be manufactured with a battery management system to provide safety for the battery, for the user and application, to maintain the health of the battery and/or to provide some other useful function such as a state of charge indicator. We know that not all li-ion batteries have a BMS and are still on public sale and sometimes an inappropriate BMS is almost the same as not having one. So when would you use one?

We would say ALWAYS!. We don’t manufacture li-ion batteries without a BMS and have signed agreements with the major cell manufacturers to say that we will not do so. It is important to them (and us) that their cells are not responsible for some of the nasty outcomes that you often see posted online. But we know there are batteries on sale and provided with products that have no BMS so why is this?

All of the reasons for using a BMS effectively boil down to managing the risk of using the battery. So conversely, not using a BMS is to ignore the risk or possibly to accept the risk, depending on where the battery is used. Let’s take a look at a few examples.

A drone powered by a li-ion battery will operate for a period of time and then lands. If during the flight, the on-board system detects the battery is getting low, then it will attempt to land by itself in a safe place, or to return home using its guidance system. If the battery uni-laterally decides to shut itself off because it believes the voltage is too low, the drone will land faster and less controlled. There is a risk either way, so it is necessary to take additional precautions and measures to mitigate the risk whether or not your battery has a BMS.

Wearable batteries are becoming common-place, heated clothing being an obvious example. If the heater element gets too hot then you will likely feel it and take off the jacket before anything serious happens. If this causes an un-protected battery to set on fire, then it will do a lot of damage to the jacket and whoever is in it. Clearly an unacceptable risk.

A toy party-speaker, bought recently was investigated. It contained a lithium-ion battery without a BMS. There was other evidence inside the box to suggest corners had been cut.

The last two examples are instances where there is no excuse for not using a BMS – only that it is a cost saving, except the damages would likely far outweigh any savings made. Worst of all, the user would not necessarily be aware of the risk. Clearly you have to have a very good reason to omit this essential piece of kit and if doing so employ other tactics and measures to prevent the worst from happening.

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