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Does the BMS of a Li-ion battery protect it from overcharging in the long run? Also is it by itself sufficient to to protect it and maintain safe health of the battery or are some other components needed to assist it?

winny
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Aasim shaikh
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    Depends on the BMS. A good BMS does everything well. A bad BMS does nothing other than sound good. Lets see the schematic and part numbers. – Puffafish Jul 27 '22 at 06:48
  • I mean, I really don't think the two questions are that related. This one seems straightforward. What does a BMS do? Maybe it has already been answered but it is not a dupe of the OP's other question. – user57037 Jul 27 '22 at 09:09
  • A BMS is meant to be a worst case protector against out of range conditions. Ideally a system will have a battery charger/controller that ensures that all aspects of battery management are optimised (subject to allowed cost and complexity). A BMS is usually a rougher tool and may not optimise battery lifetime or performance. – Russell McMahon Jul 30 '22 at 12:07

2 Answers2

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There is some variation. A typical BMS does these things:

  • Balance cells during charging
  • Disable charge at low temperature
  • Disable discharge at high temperature
  • Disable discharge if the pack or any cell is under-voltage
  • Disable charge if the pack or any cell is over-voltage
  • Disable discharge if the discharge current is too high
  • Disable charge if the charge current is too high

The BMS is a secondary or backup protection system. If the pack is in good condition (balanced) and charged and discharged correctly, the BMS should never have to disable anything.

You should not rely on the BMS cutting off charging in normal use. The charger should be designed to avoid over-charging. Likewise, you should not rely on the BMS cutting off discharge. The load should turn off automatically when the pack voltage is low, so the BMS does not need to take action.

user57037
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It really depends on the BMS complexity and cost that you warrant your battery requires. If you're talking about a multi-cell battery pack with 10s of Lithium cells in parallel and/or series then you may consider a BMS with functions more appropriate to such a battery structure (as some points already mentioned in one of the answers).

For one-cell or two-cell battery packs it is often that the "BMS" is simply a very basic PCM - a Protection Circuit Module. This is the most basic type and is really a stand-alone protective circuit and usually composed of analogue components only. It is the most simple and fundamental protection directly on the Lithium battery, providing OV, UV, OC protection that Lithium batteries require. A BMS on the other hand usually integrates some software and is usually programmable. It may also include the protective functions of the PCM or it may not, instead concentrating on other very useful functions like coulomb-counting for charge monitoring, temperature monitoring, unique ID/serial number etc. The BMS may be integrated into the battery or it may be external on a main board etc. It is also more expensive than a basic PCM as you can imagine, so it depends on your application, requirements and budget...

citizen
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