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Homemade Phone Charger Won't Charge more than 80mA? Answered

I have a homemade linear power supply that can supply 5.1V up to 1.3A. I want to use it to charge a USB device such as a phone. However, the phone is "slow charging" at 80mA. I have tried connecting the data inputs together and then tried setting both data inputs to 2.75V (I have a throw away charger that I measured that voltage from). Both results still only have 80mA going through. How can I make it so the phone accepts a higher current? Is there a specific voltage the data inputs have to be at?

I know chargers now "talk" to the phone but I'm just using my power supply as a "dumb charger". Charging the phone is supposed to be a proof that the supply can work.

I'm using a Samsung Note 4 and a Note 9 for phones to try charging.



2 months ago

My phone charges the last couple percents very slowly, might be the cause.

Jack A Lopez

2 months ago

The charger circuit on a mobile phone draws as much current as it wants to, ostensibly as much as it needs to, and never more than that.

It is kind of like if you lead a horse to water, and then the horse does not drink water as fast as you would like it to. Then what are you going to do?

I suppose you could try bribing the horse, or bullying it, or reasoning with it. Yet are any of those kind of activities going to work with a horse?

Do you think you can command your phone(s) to drink charge faster?

Do you think it is necessary to do this?

I mean, my thinking is if the phone is charging itself, at some rate, then it is doing its thing, and I should not be frustrated it is not doing it fast enough. Rather I should be content the darned thing works at all.


2 months ago

You can check Wiki for the USB charging specifications.
Apple needs two different voltages while standard Android devices usually only need one voltage on both data lines.
Additionally it also matters what type of cable you use.
Sadly I have not found the ideal solution for the last bit yet.
I have a thin and flimsy cable of 4m length that has no problems charging my phone at 2 amps.
But another one that is just 60cm long and uses much thicker wires fails to provide more than 800mA.
The newest phones now even require that the charger adjusts its output corresponding to the phone's demand and if that bit fails than the phone switches to a safe mode.
In that mode you should still get 500mA though.