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Most small LiPo batteries from any online retailer normally ship with a built-in over-voltage protection IC between the battery leads. I'm working on a single cell LiPo charger circuit and I wondered if I could just integrate that same protection circuit onto the charger PCB in case the end user attaches a battery that doesn't have one installed.

My questions are:

1) If the user's battery has the protection IC already installed and then attaches it to the PCB with its own protection IC, would having the two safeguards be redundant or interfere with each other in any way?

2) Is it a bad design practice to have this kind of a backup system if most batteries already have over-voltage protection built-in?

I couldn't find if anyone asked any similar questions before. If someone has asked before, please link them. Thanks!

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  • \$\begingroup\$ If you are specifying the smart charger you can make it monitor the charging progress and if you should detect an internal over voltage protection event before you were planning on limiting you just accept this as the appropriate choice and end charging. Adding in the protection at least at a firmware level is pretty important if you cannot guarantee the existence of the protection circuit in inserted cells. \$\endgroup\$ – KalleMP Aug 27 '16 at 19:40
  • \$\begingroup\$ No, don't add an additional protection circuit. Just make sure the charger follows best practices. \$\endgroup\$ – mkeith Aug 28 '16 at 4:41
  • \$\begingroup\$ Would not hurt to add a fuse or PTC, though. \$\endgroup\$ – mkeith Aug 28 '16 at 4:41
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1) It could be harmful if an external balancer has a lower threshold and prevents the internal controller from shutdown in a timely manner. Otherwise redundant.

2) It is not safe to assume all LiPo cells have internal OVP protection, yet smart battery packs may well have this.

An example of an external balancer.( not endorsed or tested by me)

Ebay

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  • \$\begingroup\$ So should my design stop at charging the LiPo? I guess if a user decided to attach a battery that didn't have the protection IC, then that's their choice. \$\endgroup\$ – ev3670 Aug 27 '16 at 17:12
  • \$\begingroup\$ If you are using a serial string of cells to charge, you need a balancer. If you are designing a single cell charger, you still need a 3 step regulator,,CC, CV, OFF. Smart chargers now can determine how many cells are in series. If just doing mobiles with internal regs. then it is redundant. \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Aug 27 '16 at 17:21
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If you are building a proper and safe single cell LiPo charger, there is no need for an additional over-voltage protection circuit. Your charger must be built in a way that it doesn't damage the cell, so it must adhere to the maximum voltage specification (and the maximum charging current specification).

But if you are into high-quality designs, you still might want to add protection devices, in case your charger circuit is failing. I'd go with an overcurrent and overvoltage protection circuit. Before charging I'd check if the connected battery has a voltage which is acceptable to charge it (something like 2.5V minimum depending on chemistry).

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  • \$\begingroup\$ I'm already using the MCP73831 controller to charge the LiPo, I just thought to add an over-voltage protection circuit as a safeguard. Then I was concerned if cascading protection ICs would interfere with normal operation. I opted to leave it out of the design for now. \$\endgroup\$ – ev3670 Aug 27 '16 at 22:00

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