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I'm building a small design that is designed to only take smaller LiPo packs, those that often terminate in a JST PH 2.0 connector with example below:

It seems like most of these similar batteries I find online already include some form of protection circuitry in the PCB behind the Kapton tape. Currently, my design includes a FS312F-G battery protection IC in series, for overdischarge, overcurrent, and overvoltage protection.

Will this IC interfere with the protection already on the batteries in any meaningful way? If not, can I just get rid of this IC entirely instead, if the onboard protection PCB already does the same thing?


It's important to note that in the physical design, there is almost no physical way for a user to actually connect an unprotected 18650 [or other common cell], unless they go about soldering a JST connector on and dremel out a large hole for one. If that battery blows up, that's on them-problem and don't want to increase BOM cost for unintended use cases.

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  • \$\begingroup\$ if you don't need system integration with the error conditions, you don't need to duplicate. It can sometimes be handy to eg, log and count UVP events to warn of a worn battery. \$\endgroup\$
    – dandavis
    Jul 21, 2020 at 4:45
  • \$\begingroup\$ The protection circuitry has already those features except OLP: It stops discharging if the battery voltage drops below a certain value (UVP) and it stops charging if the battery voltage exceeds a certain value (OCP and OVP). \$\endgroup\$ Jul 21, 2020 at 4:46
  • \$\begingroup\$ @dandavis I don't need to log that at all, since it's just powering a small circuit that won't have the complexity for monitoring that anyways. \$\endgroup\$
    – Felix Jen
    Jul 21, 2020 at 4:58
  • \$\begingroup\$ @RohatKılıç Seems like I'm just missing overcurrent protection then, which I can probably just add using a small PTC in series. Thanks! \$\endgroup\$
    – Felix Jen
    Jul 21, 2020 at 4:58

1 Answer 1

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It is a good safety practice that you should always have at least an extra layer of protection when dealing with Li-ion batteries.

A proper design shall have:

  1. A well designed, robust charging and discharging circuit
  2. A battery protection circuit
  3. A battery with protection circuit built-in

#3 would be the last resort in case both 1 & 2 failed.

You can easily find many designs in China skipped #2, and some I have came across even without #3 and a poorly designed #1, and with a crappy power supply. Not too difficult to imagine how these would ended up after being used for a while.

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  • \$\begingroup\$ Thanks! I've honestly seen so many boards just omit #2, so I figured that I might as well save BOM costs too. Thinking about it more though, as you mentioned, missing #3 and bad #1 would be a big problem, so I'm gonna go ahead and keep it in just in case... \$\endgroup\$
    – Felix Jen
    Jul 21, 2020 at 17:30

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