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Charging a Lithium Battery via USB

Discussion in 'Power Electronics' started by StealthRT, Sep 4, 2010.

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  1. StealthRT

    StealthRT

    133
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    Sep 4, 2010
    Hey everyone, i am looking into a project that i want to be able to charge a Seiko MS621FE-FL11E lithium coin 3.1v battery.

    I will be using the 5v from the USB and convert it to 3.3v using the LM3940. However, i am not sure what all i need between the 3.3v and the battery itself. Is there some type of protection that is needed so that the battery will not explode? I would also like to incorporate an LED that flashes when its charging and also stays lit when charging has completed.

    I've been looking at the chip MCP73833 but it looks to output (charge) with 3.7v. If that is ok to use with the 3.1v battery itself then i can omit the LM3940 and just use the MCP73833 chip with 5v to the output (charging) of 3.7v to the battery. It also has output for LED's to show status! Sound good?

    [​IMG]

    Any help would be great! :)

    David
     
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,499
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    Jan 21, 2010
    Have you checked the specs?

    the charge current is 15uA and they recommend a constant voltage charger set to 3 volts.
     
  3. StealthRT

    StealthRT

    133
    2
    Sep 4, 2010
    Thanks for the reply, steve :)

    Would i be able to use a resister between the 3.7v of the chip and the 3.1v of the battery and bring the 3.7v down to around 3.0-3.1v? Would that work or would that screw with the chip?

    David
     
  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    You need a 3.1V regulator and possibly a series resistor to limit the charge current (he writes, paraphrasing exactly what the datasheet says)
     
  5. StealthRT

    StealthRT

    133
    2
    Sep 4, 2010
    Alright, well i looked into it more and decided to do this:

    Using a Dantona LIR2032 3.6V/40mAh Li-ion Rechargeable Coin Cell
    Using a Nordic nRF24L01+ chip to be powered. (the max says its max power is 3.7v)
    Using the MCP73833 to charge the antona LIR2032 3.6V battery

    nRF24L01+ datasheet with power specs:
    [​IMG]

    Dantona LIR2032 3.6V datasheet:
    [​IMG]

    MCP73833 datasheet:
    [​IMG]

    From the datasheets, it seems doable to use the MCP73833 to recharge the 3.7v dantona LIR2032 3.6v battery. But i'm no expert so that is why i posted my idea here of using this after reviewing everything.

    Please let me know if you see a danger/potential problem with doing this :)

    David
     
  6. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    It would have been nice if you had linked to the datasheets rather than just single pages from them. Unfortunately I am in a hurry at the moment and don't have time to go off in search of them for you.

    My first feeling is that it won't work because:

    1) nominal batter voltage is 3.7V, device to be powered has max voltage of 3.6V

    2) charging voltage of battery is 4.2V, which is way higher than 3.6V.

    I think the charger you've indicated is way over the top, but it may work. Is it just a voltage regulator? The single page from the specs doesn't tell me if it has any additional smarts.
     
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