Stop mobile charging at 80% or less? Without root

[Clarkdale44]

Hello

Ever since i know how well the battery performs when charged till 80 % , i have been meaning to find a way to auto disconnect the charger at 80 %. I was wondering, is this even possible. I know there are those auto disconnect cables that does the wonder but they do it at 100 % which i don't quite like.

I was wondering if there's a way to tweak them around so that they could disconnect the charging at 80% instead of 100%.


There's an excellent mobile app to do this but damn it requires root, so can't do that either.

Or if u guys have any other custom circuit to do the job then please let me know.

Anyway Merry Christmas guys...

Regards

 

[Pommie]

I don't think there's anyway to monitor the battery voltage externally. An app could comunicate with a charger via bluetooth to tell it to disconnect, apart from that I can't see it being possible.

Mike.
Edit, thinking about it, it could be done via the usb cable but would require OTG capabilities in the charger.

 

[Diver300]

I can't think of a method that would work for all phones. You could try measuring the current and see how much it drops as the battery gets charged. You could also try reducing the supply voltage. As the battery charges, its voltage increases, and the difference between the supply voltage and the battery voltage reduces. Often that will cause the charging current to reduce. With a slightly lower supply voltage, you might find that the current reduces at a lower state of charge.

If current does drop as the battery approaches full charge, then you will just have to make a circuit to monitor the current and to turn off when the current is low enough.

 

[Nigel Goodwin]

I can't think of a method that would work for all phones. You could try measuring the current and see how much it drops as the battery gets charged. You could also try reducing the supply voltage. As the battery charges, its voltage increases, and the difference between the supply voltage and the battery voltage reduces. Often that will cause the charging current to reduce. With a slightly lower supply voltage, you might find that the current reduces at a lower state of charge.

If current does drop as the battery approaches full charge, then you will just have to make a circuit to monitor the current and to turn off when the current is low enough.

Charging for Li-Ion is easy, and well understood - you simply charge from a constant current until the battery reaches it's terminal voltage (4.2V per cell) and then switch to constant voltage. From this point the current gradually drops, and you stop charging when it reaches your target current, usually about 10% of the constant current earlier.

For a mobile phone this is all done in the phones 'BIOS' I suppose it would be?, certainly low level OS anyway - and manufacturers commonly tweak the charging system in system updates, like Samsung did to try and stop their phones catching on fire.

EDIT: Just looked up one of my projects, where I recorded a number of charging and discharging cycles, and used the data to calibrate charge and discharge battery levels, and the switch from constant current to constant voltage occurs at about 70% of full charge.