car phone chargers are weak as piss

I bought 2, one Eveready, the other Coles home brand, and neither will
charge a phone, merely keep it running with a low battery.
So I used a USB tester and compared with mains chargers.
All the chargers register 5.0 volts (only 1 decimal place unfortunately).
I tried one phone on the car chargers, and both show 0.25 A draw.
Same phone on mains chargers was 0.52 A from one charger and 0.54 A on the
other. I left the phone on charger until it was showing 100%, the current
had gone down to 0.25 A.

Then tried another phone. It drew 0.87 A on the mains chargers, but only
0.42 A on both car chargers.

Maybe both the car chargers have the same chip in them. Seems it only
delivers approximately half the current required to charge a phone.

 

[Computer Nerd Kev]

bruce56@topmail.co.nz wrote:

I bought 2, one Eveready, the other Coles home brand, and neither will
charge a phone, merely keep it running with a low battery.
So I used a USB tester and compared with mains chargers.
All the chargers register 5.0 volts (only 1 decimal place unfortunately).
I tried one phone on the car chargers, and both show 0.25 A draw.
Same phone on mains chargers was 0.52 A from one charger and 0.54 A on the
other. I left the phone on charger until it was showing 100%, the current
had gone down to 0.25 A.

Then tried another phone. It drew 0.87 A on the mains chargers, but only
0.42 A on both car chargers.

Maybe both the car chargers have the same chip in them. Seems it only
delivers approximately half the current required to charge a phone.

It's more likely that the phone is minimising the current it draws
from the charger, perhaps by deliberately not charging the battery.
The problem is likely that these cheap chargers don't use the proper
electronics that the phone expects to find in a genuine charger to
tell it what its current capacity is, so it defaults to the lowest
useful current in order to be safe (or at least do more than simply
cause the power supply to shut down completely).

See "USB Battery Charging" here:
https://en.wikipedia.org/wiki/USB_(Physical)#Power

I suspect that your cheap chargers just connect 5V to + and -,
without any attempt to follow any communications protocol with
the device. That would still work with a lot of gear, but your phones
are too smart to fall for it. If the phones use a resistance over the
data lines to indicate the current capacity, that could be added by
cutting the cable and wiring a resistor in. If they need the full
digital discussion, it would be a lot harder and you're probably
better off finding an official charger, or one that explicitly says
that it's compatible with your phone/s.

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