# High Short-circuit protection for LiPo Battery

I will be using a LiPo battery for a project, and I want to make certain that I fully understand the safety features of the Protection Circuit Module included with the battery, so that I have a safe design.

When looking at the datasheet for the battery it includes details of the PCM, and lists the limits for when the PCM protects the battery. One of the features is the short-circuit protection, which I interpret as the protection against having a too large current rushing into the battery.

The battery I am using is very small, 25 mAh, but the PCM is listed that the current limit for when the short-circuit protection starts working is 0.7A, and that the short-circuit detection time is 7.2-11 ms.

Here's my question:

• How can this be safe?
• What if I have a charger that malfunctions and does not regulate the charging current correctly, but has a current limitation of 0.5A. Could I not then have a constant 0.5A going into my battery for which the short-circuit protection does not protect for, and that my small battery would most likely not survive?

The details of the battery PCM is included below.

• The PCM usually protects against OUTPUT short circuit current. You have quoted the overcurrent delay time - the short cct delay is 380 uS max. || For overcurrent 2.1A x 11 mS x say 4V -> Joules = V x I x t = 4 x 2.1 x 0.011 ~~= 0.1 Joule - = 100 mW. seconds . It seems "rather unlikely" that that amount of energy would do significant damage. If you REALLY want a faster and/or lower current PCM you could easily enoughbuild one with a suitable fast comparator. || Do you REALLY have a 25 mAh LiPo - that's tiny - what is the application? Dec 6, 2019 at 11:46
• Consider the consequences of charging it at 0.5A. Its charge voltage will increase by 0.5A * cell internal resistance, and the over-charge protection will cut in a bit early. If the cell is designed to survive charging at 20C, it is safe. Otherwise you will need additional charge current limitation outside the protection module, which is normally not the job of the PCM. (And Russell is of course right - over-current protection usually refers to discharge protection)
– user16324
Dec 6, 2019 at 11:53
• Where did you get the 25mAh battery? Can you provide a link to the datasheet? Dec 6, 2019 at 19:41
• @BruceAbbott You can see the battery here: honcell.com/products/models/id/1667.html Dec 7, 2019 at 16:22
• @RussellMcMahon Yeah, its a really cute little battery, the application is an IoT product with really low consumption, but where a fast charge (1C) rate is required. Dec 7, 2019 at 16:23