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The functions of a BMS

What is the purpose of a BMS?

Lithium batteries are inherently unstable. When they go outside their operating range, they become a fire hazard. One of the jobs of the BMS is to ensure that cells are not overcharged or over discharged. In addition, the cell temperature must not rise too high and short-circuit protection is desirable.
What is the functions of a BMS? | Axtrel Battery Management

Protection against calamities

When using a battery, several situations occur that can cause cells to go outside their operating range. When discharging, the BMS must cut off the current if one of the cells drops below the minimum voltage (approx. 3V). And during charging, the current must be disconnected when one of the cells rises above the maximum voltage (approx. 4.2V).

Everything in balance

But after charging and discharging, cells get slightly out of balance. One cell has lost a little more capacity than another. Such an imbalance must be corrected by the BMS because the most full cell determines when the charging stops, but the most empty cell determines when the battery is empty.
A strong imbalance will then reduce the usable capacity of the battery.

Knowledge is power

In your application (e-bike, e-scooter or piece of e-tool) it is often desirable (or necessary) to have information about the battery. How full is it, how far or long can I go, when do I need to replace the battery?

In order to know this, the BMS must have a communication connection. The most common method nowadays is CANbus.

Remember the way the user uses it

To assist the support department and for the proper processing of quality information, it is desirable to keep a log of the conditions under which the battery has been used.
In our BMSs we call this the ‘Event log’.

Such a log is also useful to see if a problem is covered by warranty or not.

See also our example of a good BMS for lithium accu’s.

Would you like to know how to make a good battery?
A short telephone call will tell you a lot more.

Why is a BMS needed?

  • Protection against calamities
  • Cell balancing
  • Data communication
  • Usage data storage
⇛   BMS, Battery management system, Lithium battery

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