Our office recently installed new wall plugs with both the Type D plug outlet (South Africa) and a USB point to charge your phone straight from the wall, without the need for the little white charger that you’d otherwise use.
IF we can use electricity straight from the wall into the phone/powerpack/battery through a USB cable, what is the use of a charge and how exactly does it work?
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The wall adapter converts Alternating current at whatever voltage/frequency it’s supplied at to direct current at a voltage your phone wants.
Some wall outlets include such a adapter behind the wall plate to provide a USB port for device charging. This is an extra expense, but offers some additional convenience to the user.
Regular mains power will instantly fry something in your phone. It’s 48 times as much voltage and your phone cannot handle that.
To use this power to charge a phone, a device must reduce the voltage before feeding it to your phone. How this is done varies and deserves its own ELI5. This device is the little charger block that plugs into the wall.
Some outlets have this device built in to the outlet itself. It still does the voltage reduction, but now it’s built in to the outlet.
A charger, the plug, simply converts 120V AC electricity to 5V DC electricity. 5V DC is what all USB plugs use. They are simply power supplies, dumb ones that simply covert electricity.
Each plug also has an Amperage rating, which limits the speed/power the plug can produce. Higher amperage allows the phone to charge faster(if the phone supports that). The device drawing power decides how many amps to use, the power supply simply has a “max amperage” it can go up to.
The phone has it’s own “charger” built in, that controls the power coming from the plug, before it gets to the battery. This is the actual “charger”, a smart device that regulates the power going into the battery, charging it and preventing overcharge.
Your phone and laptop, are weird cases where we call the power supply brick a “charger” but the actual charger is in the device, the plug/brick simply converts electricity to the correct format(power supply).
So the thing in your wall is a powersupply(like the bricks/plugs) that converts electricity to the correct format. 5v DC
The electricity in your walls (in South Africa) is 230 volts alternating current (AC) at 50hz. The USB standard, which your smartphone is designed to use, supplies 5 volts direct current (DC).
To get the electricity from your wall into your phone, you need to convert AC to DC and drop the voltage. The power brick or “wall wart” you plug your phone into is a transformer and adaptor, which does just that.
The USB plug built into the wall is the same, the transformer is just built into the receptacle and hidden behind the wall.
The phone needs a very small voltage to charge safely. Voltage is like the electrical version of water pressure. To much pressure will wreck circuits. It only takes 5Volts to charge but the wall socket has 230volts. The plug-in usb charger that comes with your phone reduces the 230 volts (electrical pressure) to just 5volts using a “step down transformer” a “rectifier” and “voltage regulator” But it has extra components inside that will protect your expensive phone. If for example, the usb cable is damaged. The wall sockets with built in usb ports tend to have cheaper circuits. if that circuit burns out you cannot unplug it. Also you cant take them with you travelling.
Bigclive.com did a teardown of one of these sockets. https://youtu.be/zoZ1_aEDPos
Those new USB-equipped outlets don’t feed the phone directly from the wall. They basically just have a phone charger hidden inside them.
https://www.popularmechanics.com/home/how-to/a10138/install-an-electrical-outlet-with-built-in-usb-ports-16544006/
As for how a phone charger works: First it needs to “transform” the AC wall voltage to a lower voltage, and then “rectify” it to DC voltage. Modern phone chargers will typically have some “smart” element to them whereby they “negotiate” with the phone to determine exactly how much voltage and current to deliver. For example, a “dumb” phone charger might only be able to give a phone a “slow” charge of `5V × 2A = 10W`, but a smarter charger might be able to negotiate something like `10V × 4.5A = 45W`.
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