Thread: Can some devices be powered directly from a wall outlet?
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Old 01-19-2015, 08:20 PM   #17
davidfor
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Quote:
Originally Posted by burnafterreading View Post
incorrect as far as your claim that ALL devices not using a battery when plugged in.

my Galaxy Nexus has a removable battery (a Li-ion), and when plugged in with a microUSB cord, it'll charge the battery. while running, removing the battery causes the phone to completely shut off, and the power flowing from the USB charging port will not keep it turned on. and this is just a smartphone, not a power-hungry tablet. this is dead-easy to actually check on a case-by-case basis on any device in which you can remove the battery while using the device.
Sorry, all that proves is that an idiot designed the device.
Quote:
there's (at least) 2 ways of designing a device to run on AC-plus-DC

1 - AC charges battery only. battery feeds power to device. separate circuits.
So, how does that work? There are wires connected to the battery terminals that charge it. There are other wires connected to the same terminals to run the device. As they are both connected to the same terminals on the battery, there is a direct connection from one to the other. How does the electricity know that it has to come down the charging wires in to the battery and not out the device powering wires?

And for a Li-Ion battery, that sounds like a nice quick way to kill the battery life and possibly turn it into a bomb.
Quote:
2 - AC feeds power to device and charging circuit. when AC is gone, internal circuit switches to draw power from battery.

#1 is how most portable devices behave. there's NO interruption of power as long as the battery is connected (and in many cases, the battery is not easily replaceable anyways, so it's a safe bet)
It's not how all portable devices behave. It definitely isn't how any of the laptops I have used behave. And it isn't how my Kobo devices behave. I have opened them and run them with a cable connected and the battery disconnected.
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