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Thread: tablet always on charge, big or low (car)batterie drain??

  1. #1
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    tablet always on charge, big or low (car)batterie drain??

    hello guys. i start this thread, becouse, no matter how i research, i cant find a specific answer, to as "the tablet will drain the battery?".
    so, my situtation is like this:
    i will use a tablet as a speedometer,so it has to be completly automated, and responsive.the thing is, i drive my car, only like once a week, and not for long drives, so even IF the tablet would last a week on sleep, it wont fully charge when i drive the car...

    My fist thought, was to use an automated system (arduino) to auto charge the tablet, like every 2 days, but in that way, i cant use the tasker app. to auto turn on the tablet..

    so i thought, to do the opposite. have the tablet always on charge, with a switching psu, and when i turn off the car, REMOVE the tablet from charge. that way i can have the tablet always charged, and also use tasker to auto turn it on and off.

    so the concerns would be those: (Asuming you have a second battery, isolated, and AGREE that batteries are meant to be discharged (otherwise they would not be called batteries... )

    1)what would be the effect of continious charge , in the lithium-ion batterie?
    as i see, it want have a probelm.. tablets and laptops ,have sofisticated circuits to control their charge, so, overcharge , is not an issue!! ( ??)
    2) what would be the drain in the second batterie ??
    from what i see, after the tablet fully charges, it only needs as power, as it consumes. (??? ) so, the real question is how much power the tablet uses in deep sleep...
    using an app (current widget) , you can make a graph of the "actual" mA consumption of the tablet. when it is on, it varies from 400mA to 1000mA BUT , when the tablet sleeps it goes from as low to 1mA(?!?!) to 30mA... wich to me seem extremly small to be true... but if that is the case, then the tablet(withe the dc-dc converter) , will never draw more than 100mA , and the car batterie , would last for weeks, without a problem....


    what do you guys think???
    Last edited by settra; 12-18-2013 at 02:30 PM.

  2. #2
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    Personally I think you leave the tablet hooked up and charging all of the time. Most tablets will allow you to leave them plugged in and only charge when they are not 100%. Only display the monitor when the vehicle is turned on. If you have a blue tooth ODBII connector maybe you could have it monitor that port for activity and disable the screen when there isn't any. Or if you have another way to detect if the car is on or off use that and turn the screen off when not needed.

  3. #3
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    yiap. turning the tablet OFF, is rethar easy. i dont have a bluetooth, but my car diagnostic is arduino, so i can monitor the serials send from arduino (And if none are received since the car is off, turn the screen off (1) .) but i will have this only as a "difensive system" , becouse as i plan i will use this a relay(hooked as normaly closed), driven by the ACC signal, will control the power to the dc-dc. tasker will have :: state:dc_power_off -> turn the screen on, state:dc_poweron ->turn the screen off.

    so the only problem i can think of, is IF the car battery drains, then the switching DC-DC will turn off, and the tablet will turn on, without the car running (and here comes the (1) , which will make sure the tablet turns off)


    P.S : turning the tablet on , with tasker, with anything else than power states, is a reall pain in the ***. when the tablet sleeps, the usb OTG shuts down, after 5min, so, if you plug a usb, the tablet has no clue... (and allot other problems)

  4. #4
    Raw Wave treetop777's Avatar
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    LoL reading this gave me a headache! Talk about over-thinking a minor problem. Like the other poster said, leave the tab plugged-in with constant power (directly) from the battery. As far as i know, when the tab is fully charged, it will stop charging even if it's still plugged-in. Doubt if tab will drain the car battery since the screen is off and it's not doing much (if anything); Unless there's still a bunch of stuff still running (GPS, WIFI, Mail, facebook, weather, time..).
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