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I am designing a custom PCM (protection circuit module) for Li-ion cells provided by a supplier ( they offer PCMs but they do not meet our RF immunity spec ). The supplier-provided PCMs have a charge / discharge limit set for 1.7A - 4A for a 240mAh battery and a 4A - 8A limit for a 1800mAh battery. Now these limits seem huge to me, so I'm wondering what a more reasonable charge discharge current is where you could still get reasonably high instantaneous current without damaging the cells.

Since the 240mAh battery is used for a BLE (Bluetooth Low-Energy) device, I doubt it will ever see more than 50mA peak. Right now I'm thinking of setting the battery protection IC to limit charge / discharge at max ~500mA current.

For the 1800mAh hour battery, I am considering a max limit of 3A. Expected peak current from this battery would be about 2A.

Are there commonly used guidelines for the Li-ion cell capacity and charge / discharge current limits or are they totally application dependent? From my search, PCM current limits vary wildly so I am curious to know what (if any) standards exist.

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This isn't really an answer, but cells (dependent on both type and particular construction) obviously have a maximum C-rating for charge and discharge which you should always stay below.

But if you know that your application isn't going to need to draw anywhere near the maximum current that the battery can safely provide, then you could limit things to be more in line with what your circuit runs at since anything above that means something is wrong (like maybe a short, but not so bad a short your battery is pushed beyond its limits).

If you are going to use limits similar to fusing then maybe double your expected operating current. You don't want the PCM kicking in for peaky, but normal, operating currents.

PCMs also probably have some type of filtering going on which would help filter out high but short peaks since it's really heat that kills the battery, not current.

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  • \$\begingroup\$ So presumably, a default PCM would have such high limit range (1.7A - 4A for a 240mAh battery) because either a) the manufacturer wants to cover a broad spectrum of power demands or b) they are simply don't take the time to design a PCM for that specific battery? \$\endgroup\$ – Konstantin Dubovenko Aug 16 '19 at 22:37
  • \$\begingroup\$ @KonstantinDubovenko I would think they just don't know what the battery is being used for. The upper limits of the numbers you gave is 15C which is consistent with the maximum safe discharge for a Lithium battery but still retain reasonable lifecycles (at least for LiPo and LiFe. I am not sure what the number is for Li-Ion but Li-Ion is known for lower maximum discharge than the former two so that might be the actual maximum maximum.) I always actually thought the maximum discharge for Li-Ions was significantly lower...like maybe 5C or less but I have nothing to back that up. \$\endgroup\$ – DKNguyen Aug 16 '19 at 22:49

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