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Is there an integrated circuit or a conventional circuit topology to monitor edge conditions of a 12 V battery pack without measuring individual cells within that unit?

A conventional BMS or battery protection-only IC offers monitoring of individual cells in a branch of cells in series. However, the 12 V battery of interest has no option to monitor individual cells inside the pack.

The battery cell technology I'm aiming for in my application is LiFePO4 which might already have some form of internal BMS installed. Nevertheless, I would like to know how battery protection is handled for batteries without an internal BMS.

The problem is that conventional multicell ICs respond to voltage/current ranges for individual cells (say, for a 3.7 V Li-Ion battery the overcharge voltage detected by given IC might be around 4.4 V). For example, a 3S protection IC's typical connection is shown below:

enter image description here

I assume such an IC can't be used for a 12 V battery pack and should not be connected like this:

enter image description here

If such a connection type would be applicable then compounding of individual voltage cell edge voltages would have to match the edge voltages of a selected 12 V battery pack.

Should I design a dedicated circuit that would respond to edge cases of a given 12 V battery, or do such integrated circuits, made for this exact use case, exist on the market? Should I abandon idea of seeking proper battery protection for such a battery and select one with an internal BMS instead?

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  • \$\begingroup\$ MucaGinger - Hi, Where did the original diagram come from? In order to comply with the site rule on referencing, details of the original source of copied / adapted material must be provided next to that material. If the original source is online (webpage, PDF, video etc.) then please edit the question & add its name & link (URL). If the original source was a printed book or other offline material, then edit the question & add a normal citation (see the linked rule for details). TY \$\endgroup\$
    – SamGibson ♦
    Commented Mar 23 at 22:08

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No, there isn't.

There is no way to protect a Li-ion battery with 2 or more cells in series without access to the inner connections between cells.

That is because you cannot infer anything about the voltages of each individual cell from the total battery voltage. For example, if the total voltage is 11 V, you could not assume that the cell voltages are 3.67 V each. Instead, they could be 1 V, 3.6 V, and 5.4 V, which also adds to 11 V. The 1 V cell would be irreparably damaged and the 5.4 V cell would be close to catching on fire.

However the battery of interest has a 12V output and has no option to monitor individual cells inside of the whole pack.

If that battery already includes a protector BMS, then it has connections to the individual cells, so you don't need to add an external BMS.

If that battery does not include a protector BMS, then it is dangerous and must not be put into use.

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  • \$\begingroup\$ In case a battery has BMS circuit internally, are there any other forms of possibly secondary protection required by convention? Or can such a battery be directly used as power supply source (to be further processed via DC/DC converters)? \$\endgroup\$
    – lucenzo97
    Commented Mar 23 at 21:18
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    \$\begingroup\$ "In case a battery has BMS circuit internally, are there any other forms of possibly secondary protection required by convention?" No. "can such a battery be directly used as power supply source (to be further processed via DC/DC converters)?" Yes. \$\endgroup\$
    – Davide Andrea
    Commented Mar 23 at 22:25
  • \$\begingroup\$ I'm sure there are battery protectors on the market for such a purpose, though. Out of curiosity what would be the most viable option here? Most reasonable idea that comes to mind is a microcontroller equipped with ADC/DACs and current sensing capabilities that would mimic features of a coventional, single-cell battery protection IC. \$\endgroup\$
    – lucenzo97
    Commented Mar 26 at 19:59
  • \$\begingroup\$ "I'm sure there are battery protectors on the market for such a purpose," If something is sold as such, it does not protect the battery. It just can't. \$\endgroup\$
    – Davide Andrea
    Commented Mar 26 at 20:21
  • \$\begingroup\$ How else would a battery protection be made? Some ADCs and some logic, I guess? Power switches need to be added externally. Seems pretty much like how protection IC is made. \$\endgroup\$
    – lucenzo97
    Commented Mar 27 at 20:13

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