Owner Manual
In the relationship between a smartphone and a USB charging port, it’s
the phone that has the power.
That’s because mobile devices, like phones and tablets, largely
determine how much power they draw when charging. Yet many people
believe it’s the USB port that’s in control. That’s just one of the common
misconceptions surrounding USB charging. Another is the amount of
power a device needs to charge.
Dispelling these myths is important because USB chargers, like
those integral to a receptacle, are becoming more common in
commercial, public and residential settings as the number of mobile
devices people own continues to grows. Users prefer USB charging
because of the convenience: They don’t have to carry around a
charging brick or AC adapter.
However, many end users, specifiers, and professional installers do not
fully understand the USB charging needs for their space. Often, they’re
operating under the assumption that more power advertised at the USB
charging receptacle equals faster charging — for example, that a USB
receptacle with 5-amps of charging capacity will always charge devices
faster than a 2-amp product.
THERE ARE THREE SIGNIFICANT PROBLEMS WITH THAT THINKING:
1
Again, the mobile device determines how much current to draw from a
port. Current draw is largely based on the device’s internal electrical
schematic and also how much charge it needs. A phone with 5%
battery life will usually demand more current than it will at 90%.
2
Most devices need far less power than people realize, as we’ll show
in the next section.
3
The total amperage advertised at the receptacle is typically shared
across ports. A phone plugged into a 5-amp receptacle with four
ports is not getting all 5 amps.
WHAT YOU DON’T KNOW ABOUT
USB CHARGING
BY KEVIN KOHL
Product Manager, Electrical Wiring Systems Division
MORE AMPS IS NOT
NECESSARILY BETTER
MOBILE FACTS
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79%
60%
of people say their
smartphone makes
them feel productive
of people in all major
cities reported anxiety
from a low or dead cell
phone battery
Source
Source