Using Tablet Without Battery

Discussion in 'Off-Topic Discussion' started by vivitern, Dec 9, 2017.

  1. vivitern

    vivitern Junior Member

    Dec 9, 2017
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    Tablets have gone mainstream a few years ago, and Li-Ion batteries have a lifetime of a few years only. This paves the way for a new need for us couch potatoes: to be able to use a tablet when the (Li-Ion) battery is no more reliable and has to be taken out (and no replacement is available).

    In order to make my question the more general possible, since I believe many will benefit from advice on how to tackle this problem, I'll have to be overly wordy.

    The problem:

    • a) A tablet (for which we assume we have no schematics) whose battery has ballooned to the point it popped open the chassis
    • b) no replacement battery available from the manufacturer or seller; other batteries of similar capacity are too big to fit
    • c) it appears it is not possible to run the tablet without a battery with the charger only, and leaving the ballooned battery in is a bit too risky.
    The idea for a solution:

    To use a suitable circuit that will simulate the battery presence so that the tablet can be run when attached to the charger (we assume that with the original battery fully discharged the tablet runs ok). The circuit might use a smaller battery and or a supercapacitor or some other magic gizmo to do what follows (note: only point I is strictly required):

    • I) MANDATORY - operate the tablet while connected to the charger with no battery inside. In this case a smaller battery or supercapacitor (or even capacitor) will only act as a buffer to protect the mobo (this should be easy), while some other circuit might be needed to fool the tablet in believing there actually is a battery and it is being charged (this might be tricky). Let's say that the main purpose here is to avoid a ka-boom.
      If necessary, a custom charger (or to be more precise, power supply) can be built form scratch (either with a 7805, LM317 or a DC-DC converter like DS1200D: DS1200D - DALLAS - DC DC Converters - Kynix Semiconductor) - there are no problems in finding a schematic for that.
    • II) OPTIONAL - the smaller battery or supercapacitor should act as a temporary buffer to power the tablet for a handful of seconds to allow for a soft shut down in case the charger is accidentally disconnected.
    • III) OPTIONAL - the additional circuit might fool the tablet into believing there is a battery (as above), and that it has been charged to the point it is possible to update the OS (I have read, for example, that the Nexus modifed to run with directly with the charger won't update unless it detects a charged battery).
    Pointer to reference needed:

    To implement point I) we need to know

    1. What storage element to use: would a (flat, <9mm) supercapacitor do?
    2. Can we simply hook that up with a diode to the charger leads on one side and to where the battery leads went on the the mobo?
    3. Do we need a thermistor to fake an overheating protection?
    To implement points II) and III) requires knowing:

    1. How do (most commonly used) Li-Ion batteries communicate with the motherboard
    2. Is it possible to create a custom circuit that fakes the communication for "battery is ok, and it is 100% charged", small enough to fit in a battery form factor?
    3. Is it possible to infer how the charging circuit works by looking and the PCB of motherboard and battery protection?
    Answers to single points are welcome. Partial solutions can be used as starting point for tackling one's specific problem. If needed I can post pictures of my tablet circuits but that would defeat the purpose of generality.

    (I see this question has been put on hold to be closed. I had a look at the guidelines mentioned below, and I do not think they apply to this case. This is not a "repair" question for a single device. This is a general question on how to create a new circuit that will make all those tablets with dead batteries work again. I am not claiming that doing so will revert climate change but a couple of polar bears, those might be saved)
  2. Spider

    Spider Administrator Staff Member

    Mar 24, 2011
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    Chicago, IL
    Tablet / Device:
    NOOK Tablet Stock NOOKcolor Rooted/Flashed Nexus 7 (2013) 32GB Stock

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