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Automatically Battery Disconnect

Former Member

It is recommended that for optimal operation a battery (laptop, phone etc.) must be maintained at a charge between 40$-80% never more, never less.

 

I am trying to build a circuit that hooks on to either my laptop charger or my phone charger and is able to ready the present battery status and turns on or turns off the charger based on if the present charge is less that 40% or more than 80%. It seems like a firly easy thing to implement but I haven't come across any mention of this on the internet. I would appreciate any help with this.

 

Varun

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  • 0

    I Think a good approach would be to monitor the current being consumed by the existing battery charger.  Battery chargers for lithium batteries are constant current source. The current should drop sharply when the battery becomes fully charged.  Breaking the circuit at that point would stop any top off charges tha follow. 

    This method also makes construction easy since a small circuit can be installed into a short cords receptical.  A torrid and an op amp can detect the current drawn.  A relay driven by a 2N2222A2N2222A transistor can be controlled by a 7474 flip flop.  Then the dropping current when the battery gets fully charged will generate a pulse that can be used to change the state of the flip flop and de-energize the charger that is plugged into the cord.   To reset the cord could be unplugged and plugged into the wall again.

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  • 0

    I Think a good approach would be to monitor the current being consumed by the existing battery charger.  Battery chargers for lithium batteries are constant current source. The current should drop sharply when the battery becomes fully charged.  Breaking the circuit at that point would stop any top off charges tha follow. 

    This method also makes construction easy since a small circuit can be installed into a short cords receptical.  A torrid and an op amp can detect the current drawn.  A relay driven by a 2N2222A2N2222A transistor can be controlled by a 7474 flip flop.  Then the dropping current when the battery gets fully charged will generate a pulse that can be used to change the state of the flip flop and de-energize the charger that is plugged into the cord.   To reset the cord could be unplugged and plugged into the wall again.

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  • 0 in reply to jaykretsch

    Thanks for your reply Jay, but as I said I want to disconnect it at 80% of its full charge not at 100% and turn it on back again at 40%. This is what is recommended for optimum battery life to maintain the charge of the battery between 40%-80% of its full. You should be able to get the present charge status from the PC through a USB with an appropriate script.

     

    Varun

  • 0 in reply to Former Member

    Varun Ramesh wrote:

     

    This is what is recommended for optimum battery life to maintain the charge of the battery between 40%-80% of its full. You should be able to get the present charge status from the PC through a USB with an appropriate script.

     

    Varun

    Not if you're using it! If you are querying the battery status via USB then the PC is on.. So why chew up battery charge cycles for no reason?

     

    It's one thing having a battery charged to 40-80% of capacity, but another thing actually running the laptop until the battery drops to 40% and then charging it again.. You're using battery cycles for no reason.

     

    Better to actually let the PC stop charging the battery and let the PC run off the mains adapter.

     

    Or if you're still worried, just physically detach the battery and run your laptop off the mains power.

  • 0 in reply to shabaz

    Well my laptop has a primitive battery control system and does not turn off the power when its fully charged.

     

    At the end of the day its a trade off right? If I imporve my battery life by maintaining charge between 40-80% even though I use up battery cylces I still emerge a winner as compared to if I do nothing about it.

    I'm too worried about my battery, its just something I would be interested to do and see if it actually makes any difference.

     

    Varun