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Thread: using laptop battery as second battery

  1. #1
    Constant Bitrate eugenweij's Avatar
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    using laptop battery as second battery

    can it be done?

    I have a practically new laptop battery and I would like to use it as a power source for my carpc when it is in sleep mode, I just dont have any idea on how to setup the wiring for that.

    the battery is rated 10.8V 4400mAh 48Wh

    I know for a battery to charge the input voltage has to be higher to create the 'push' needed to charge.
    my question is basically how to wire it to my m3 atx power supply, because the m3 atx will turn off the 5v rail if the car battery will go below 11.8V

    any thoughts on the matter are welcome
    View my worklog here

  2. #2
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    Need to figure out what pins do what on that battery, measure out voltage while charging, full while plugged, and on battery alone.That's as far I'm any good though. I would think you need to discover if there's an extra circuit on your laptop that deals with the battery. Also need to know if it is a pull through type of circuit on the laptop where when the battery is removed the laptop doesn't function.

    Other problem is that it only kicks out 10volts. Your motherboard probably wants 12B.C. Also have to figure out switching between the m3 and battery. Going to need a 5 volt output from that battery too.

    Just my .02
    Last edited by YelloEye; 11-23-2012 at 09:49 AM.

  3. #3
    Constant Bitrate eugenweij's Avatar
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    the 10 volts isn't an issue , I will be using it to power my PC in sleep mode , which only requires the 5V rail to be powered , just not sure how to connect the battery to my system for it to be charged and only supply power to the 5V rail when the PC is in sleep mode

    as for the connectors on the battery I am aware they need to be figured out , but before I start worrying about the battery, I want to see what other peoples thoughts are on the matter
    View my worklog here

  4. #4
    Raw Wave
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    Make sure you use a charger appropriate for that battery - ie, current limiting, "knee point" sensing, maybe temperature sensing. It's certainly not just a matter of charging from a vehicle's 12V system.

    And if it's LiPo or lithium, be especially aware of explosion issues (I think that was a charging issue).

  5. #5
    Constant Bitrate eugenweij's Avatar
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    yes I am planning on creating a circuit for it so charging happens in a controlled manner, the charger for that specific laptop rates 16V out so I guess I will have to fab a small power supply for it or something like that , and have a converter to convert battery voltage to 5 volts, which is all I need basically from the battery
    View my worklog here

  6. #6
    Raw Wave
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    Don't confuse the laptop's supply with what the laptop internally provides its battery (ie, thru its internal charger).


    In 12V vehicles, most would use a 2nd 12V lead-acid battery (else whatever battery type they have if not 12V or lead-acid) using whatever isolation system is appropriate.

    To charge laptop and other batteries in vehicle, people would usually buy the appropriate 12V charger since that is usually easier else cheaper than building one.
    Of course that battery's voltage has to be converted to suit whatever it is powering, ie 5V in your case.


    PS - you'll probably find buying a 12V lead acid is far more economical in that it will last longer life-cycle wise.
    Last edited by OldSpark; 11-23-2012 at 04:00 PM. Reason: PS ...

  7. #7
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    Hi
    Not sure but I think laptop batts are balanced charged (reason for all the pins on them) this makes it more difficult to come up with a charging solution

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