DIYbanter - View Single Post - Advice sought on why 6.8A USB charger melted USB cable today

M Philbrook

In article , says...
"Charging Combinations:
- 2 tablets + 3 mobile devices
- 1 tablet + 4 mobile devices
- 5 mobile devices
- 3 tablets"

I am confused about both the pure math and how this operates.

Q1: Since 6.8A times 5VDC is only 34Watts (not 40 Watts), how
can they very clearly label it as a 40Watt device?
Yes, the supply/charger is using a total of 40 watts, some of which
gets lost with in itself the remainder used for the connected devices.
One could say it's 85% efficient.

Q2: How does the device "know" to give tablets 2.4 Amps
(12 Watts) but a "mobile device" only 1Amp (5 Watts).

Q3: What if a mobile device "wants" more than 1 amp?
Does the charger give more than 1A to the device?

Many devices can link up to things like PCs. The USB port
has more than just power/charging wires. They also have
data wires.

Its posible the charger could be detecting basics about the
device and selecting a current via the data lines.

On devices that it can't determine the ratings, it may
deside to give it all!.

Jamie