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Problems with Battery Protection Circuit

Discussion in 'General Electronics Chat' started by Kian, Aug 3, 2017.

  1. Kian

    Kian Member

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    Hi all,

    I am designing a circuit that runs on a single rechargeable lithium ion polymer battery. The battery does not come with any inbuilt battery protection circuit so I implement my own protection circuit based on S-8261. I followed the same exact design in my application:

    [​IMG]


    The battery is connected to VDD and VSS of the S-8261. And I am using EB+ and EB- as the VCC and GND of my circuit. I also have a 3.3V LDO voltage regulator connected to EB+ and EB-.

    The problem I am facing now is that when the battery is connected, there is no voltage on EB+ and EB-. Only when I short circuit battery negative terminal to EB- momentarily , then everything will start working normally. I can remove the short circuit and there is a voltage across EB+ and EB-. I don't know what is the cause of it. Can anyone help or advise?
     
  2. cowboybob

    cowboybob Well-Known Member Most Helpful Member

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    What are you using as the battery charging source/circuit?

    From your description, your assuming the EB+ and EB- are the output of the circuit, rather than the charger input points.
     
  3. Kian

    Kian Member

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    Hi,

    I am using a lipo charger IC, MCP73831. It is connected to EB+ and EB- to charge the battery.
     
    Last edited: Aug 3, 2017
  4. dave

    Dave New Member

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  5. cowboybob

    cowboybob Well-Known Member Most Helpful Member

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    I don't understand why you have your circuit connected this way.What are you using as the charger?

    Please give us a complete schematic of your entire circuit as wired.
     
  6. Pommie

    Pommie Well-Known Member Most Helpful Member

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    I recently built a circuit using the same charger but with a boost regulator for the output. The battery I used was a 1AH Lipo from Sparkfun. The battery has built in protection to stop over discharging. I posted the schematic in this thread - is yours similar?

    Mike.
     
  7. Kian

    Kian Member

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    Hi,
    I am quite sure my circuit is correct. When you buy a lipo battery with built in battery protection, it has almost the same circuit inside and the two wires coming out from the lipo battery is connected to the + terminal of the battery (red wire) and the EB- (black wire).

    My complete circuit is given below:

    [​IMG]
    [​IMG]
     
    Last edited: Aug 3, 2017
  8. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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  9. Kian

    Kian Member

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    I have limitations with the thickness of the battery and none of the lipo batteries in the market with built-in battery protection fits my requirements. I will need a bare lipo battery without the protection circuit and I need to put the battery protection circuit on the PCB instead.
     
  10. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    The board and circuit I posted is for unprotected LiPo's - either use the small boards, or copy it to your own PCB :D
     
  11. Kian

    Kian Member

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    But if I followed the reference design, it should work! But it isn't. Is there any way to troubleshoot this?
     
  12. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    The pin numbers on the dual FET seem to be different to those on the circuit I posted, you might like to check which is correct.

    You're also a little hopeful if you think that datasheets are always correct!.
     
  13. alec_t

    alec_t Well-Known Member Most Helpful Member

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    :confused: I don't understand your use of the S8205A if you have a single-cell battery. That IC is intended for a 4-cell or 5-cell battery.
     
  14. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    It's just a dual FET (not an IC at all), and equally suitable for a single cell - and used in the board I linked to.
     
  15. alec_t

    alec_t Well-Known Member Most Helpful Member

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    Ah, seems like the same code is used for two different things :rolleyes:. Here's the IC.
     

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