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2 cell lipo battery indicator

Discussion in 'Power Electronics' started by knubs, Mar 10, 2011.

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  1. knubs

    knubs

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    Mar 10, 2011
    hi, i am working on a little project and require some guidance. i want to build a battery indicator for a 2 cell lithium polymer battery. i just want a simple led light system that lights up more led's in a row as the voltage increases and goes down to one led when it's dead.
    any suggestions on how to make this happen is very appreciated, and if you know where i could get one premade let me know. i have one hand so it does complicate things, so if i can buy one that just saves me the effort of building it.

    Thank you very much!
    ,knubs
     
  2. knubs

    knubs

    3
    0
    Mar 10, 2011
    oh, and i'm just starting to get more into electronics so could someone point me to a place where i can learn how to understand circuit diagrams? i am good a soldering but i dont know how to read those diagrams. all i see is a bunch swiggly lines and triangles and such.
     
  3. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,411
    2,779
    Jan 21, 2010
    If you want to make one yourself, you could google a "LM3914 expanded scale voltmeter".

    With LiPo, complete discharge is probably around 3V per cell, so for 2 cells, 6V represents completely empty. Around 8.4 volts is fully charged.

    However there are risks that once cell will charge/discharge faster than the other, so when the pack reaches 6V, one cell may be at 2.5V, and the other at 3.5V. The same issue can arise while charging.

    There are some devices that show the voltage on several cells in series. They're probably so cheap that you wouldn't be easily able to make them for less.

    Here is one.
     
  4. knubs

    knubs

    3
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    Mar 10, 2011
    i dont have a balancer on that battery so they could be a little uneven, but it should be close still. i would just like to build a small meter that reads the cumulative voltage of the two cells. it wouldnt have to 100%,just phone battery meter status to give a rough idea. i plan on using it on an item i use daily, and through out the day i just need to see when i'm going to loose power (before the cut off for the lipo). i personally would be fine with a little voltage display, but others will be using it to, so it has to be easy to read. is there anyway to convert one of those to led's instead of a readout?
    and i will google that, thanks!
     
  5. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,411
    2,779
    Jan 21, 2010
    You probably want an expanded scale voltmeter then (as I suggested above).

    You can buy them, or you can google for circuits and make your own.

    Circuits using the LM3914 (there are other options too) can give you a nice dot or bar graph display. I built one *many* years ago for a car battery that read between 10 and 15 volts (from memory)
     
  6. part_time

    part_time

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    Jan 18, 2011
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