Li-ion Battery Protection

Discussion in 'Power Electronics' started by Dr.killjoy, Jul 18, 2016.

  1. Dr.killjoy

    Thread Starter Well-Known Member

    Apr 28, 2013
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    I have been working on a small li-ion charging circuit for my 18650 cells .. But I wanted a low voltage indicator but figured I would better off with a battery protection circuit.. I know there are alot of parts out there for this job but I don't want to buy anything premade.. So I am looking for a IC/Parts and would like some help or suggestion on attempting this ??
     
  2. BobTPH

    Active Member

    Jun 5, 2013
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    18650 cells with the protection built in are available, in fact I think they are the more common type.

    Bob
     
  3. Dr.killjoy

    Thread Starter Well-Known Member

    Apr 28, 2013
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    Thanks and I am not looking to buy new cell because I already have a nice stash but just unprotected cells...
     
  4. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    Home-brew is commendable, but in the interests of safety it might be wiser on this occasion to use available dedicated protection circuits.
     
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  5. ian field

    Distinguished Member

    Oct 27, 2012
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    Maxim do a small selection of voltage monitor chips.
     
  6. Dr.killjoy

    Thread Starter Well-Known Member

    Apr 28, 2013
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    Thanks for the concern. I understand what ur saying but I really need to learn how to build these circuits and why & how they work.. Plus I have been learning they most stuff made in china sucks and doesn't always work or even right..
    Thanks I will have to check them out..
     
  7. electrophile

    Member

    Aug 30, 2013
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    TI has a nice selection of devices for this.
     
  8. ian field

    Distinguished Member

    Oct 27, 2012
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    For several years now, I've been using a TL431 based shunt regulator for my E-cigarette.

    So far - I haven't bothered with low voltage shutdown, but the E-cig uses a logic level MOSFET controlled by a low rated tact switch pushbutton. That is a UVLO of sorts when the cell voltage no longer exceeds VGSthr.
     
  9. Dr.killjoy

    Thread Starter Well-Known Member

    Apr 28, 2013
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    My plan was to use a proper timed charge ic to charge the li-ion. I realied that I needed some kind of low voltage protection to keep the cell healthy.. Your circuit seems pretty cool and will have too look into it .. Would you happen to have the schematic ??

    Thanks
     
  10. ian field

    Distinguished Member

    Oct 27, 2012
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    It was published in Elektor a few years back - I sold them the rights to it.

    There's an updated version recently sent, they haven't contacted me yet.

    The shunt regulator must handle all the charging current when the cell reaches the specified terminal voltage - the basic TL431 can sink 100mA.

    You can boost the current capability by making a hybrid Sziklai pair with the TL431 and a PNP power transistor.
     
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