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.
A short telephone call will tell you a lot more.