5 May
2012
5 May
'12
12:06 p.m.
Eric Smith wrote:
Pete Turnbull wrote:
If you have it on and hooked up to a 1A USB charger (port or standard
USB charger) while it won't charge, it won't really discharge (much )
either - so it isn't exactly lying - it is NOT charging if you are using
it, but asleep or off it will charge (faster if completely off).
John :-#)#
For example, an iPhone can pull far more current
than USB guarantees
(well over an amp), so it tests first. The proper charger has a
couple of voltage dividers across the power such that the data +/-
lines are held at specific voltages even at light load. If the
voltage on each is within a specific (fairly narrow) range the iPhone
knows it can pull at least an amp. A different range tells it 500mA.
Else nothing.
The iPad is obnoxious about this. If it can't get the extra current
it wants, it tells the user that it won't charge. It lies, though:
actually it does charge, but slowly.
This had me in a panic when I first found out about it after having
flown somewhere. I assumed that I could charge it from my laptop, and
didn't bring the iPad charger. The first evening the battery was low,
so I plugged it into the laptop, and it told me that it wouldn't
charge. I thought I was out of luck for the whole trip, but it
actually did manage to charge overnight.
They really should change the message to say that it will take a long
time to charge, rather than claiming that it won't charge at all.