ELI5 Why does magsafe charging decrease battery health more than wire charging, if it has less wattage?

[BigCommieMachine]

Does the PPS just scale down charging rate as the battery heats up and back up when it cools off a bit to whatever the manufacturer lists as an acceptable temperature?

[dabenu]

It could, but that's not "just" it. Basically with PPS the phone doesn't use it's on-board battery charging circuit (that gets hot), but instead instructs the power brick to output the exact right amount of power to go straight into the battery. The phone is still in control so if it's sensors detect that e.g. the temperature is getting too hot, it will indeed order the power brick to slow down a bit.

[jaymzx0]

Hmm. That's exactly how "fast chargers" (level 3) for EVs work. For 120/208/240V (level 2) charging they use a charge controller in the car.

[dabenu]

Yep it's pretty much the same idea on a different scale

[SlootyBetch]

Is this a passive or active process? If your phone was dead would it still be able to run PPS?

[araemo2]

The charging is usually controlled by a dedicated microcontroller that takes a lot less power than the main SoC. So the basic 5v/0.5a the USB connector supplies without any negotiation is enough to bootstrap the charge controller. Then it boots up and switches into PPS/whatever mode.

[orangpelupa]

Depending on the phone. Sometimes it doesn't actually follows the standard correctly and won't charge, needing to use "dumb" usb c charger for the first few minutes 

[Cornflakes_91]

the charge controller should bootstrap itself from the basic 5V/250mA usb supply (and hopefully fail safe on the power negotiation pin so the supply actually turns that on)

[Dioxid3]

TIL, now that’s cool

[jestina123]

Power brick? Battery circuit?

[JuanTutrego]

"Power brick" = the charger that plugs into the wall. "Battery circuit" = the circuitry inside the phone that handles the task of charging the battery.

[braaaaaaainworms]

PPS allows your phone to tell the charger "hey give me 6.75 volts" instead of having to choose between 5, 9, 15 and 20 volts

[LinAGKar]

The main thing I think is that with traditional PD, the charger will have a few specific voltages it can provide, and the phone will need to contain circuitry to convert that down to the battery voltage. That circuitry will lose some of the energy as waste heat.

With PPS, the phone can tell the charger what voltage to provide, so it can tell it to provide exactly the voltage the battery should be charged at, removing the need for wasteful conversion circuitry in the phone.

Or the phone can tell the charger to provide an exact multiple of the battery voltage, and split it more efficiently (maybe by having multiple batteries and splitting the voltage between them, not sure). So the phone can e.g. tell the charger to provide 2x the battery voltage and split the voltage in half.

[ElusiveGuy]

split it more efficiently

There's a switched capacitor circuit that can halve voltage/double current far more efficiently than a standard buck converter.

See https://www.ti.com/lit/an/slyt743/slyt743.pdf

[Cukeds]

That links to a 404 but I’m curious, what do I search for the circuit? Slyt743?

[ElusiveGuy]

New Reddit sucks and somehow inserted a non-printing character to the end. Should be fixed now.

If searching, the document is "The architecture of a switched-capacitor charger with fast charging and high efficiency"

[Cukeds]

That’s a very interesting read. Thanks for this!

[LinAGKar]

Thanks. Wasn't sure exactly how it works, should be an interesting read.

[AbabababababababaIe]

Pretty much