Why I need a 20W PD Charger For MagSafe
I got a iPhone 12 and MagSafe charger days ago, Apple recommends using certain 20W PD adapters — and they don't need to buy from Apple, despite what you may have heard from Third-party accessories.
Today,I will explain what these requirements are and why an old 18W adapter cannot meet them.
Apple has unveiled a new line of iPhone 12 models with a new accessory and charging system called MagSafe.The name was previously used to refer to a magnetic quick-release cable in Apple's portable Mac line, but it was lost after Apple switched to USB-C.
What is MagSafe?
In this case, MagSafe refers to the magnetic ability of the accessory, not the safety it provides .An accessory released is the MagSafe charger, which is a large charging dock that can be connected to the back of the iPhone 12 for wireless charging. Unlike other wireless chargers, it magnetically holds the iPhone when in use, which means you can pick up and use the iPhone while charging.
The large surface area coupled with Apple's own proprietary design allows for up to 15W of delivered power to a device when charging,While using the MagSafe charger vs only 7.5W on Qi chargers. The ability to charge at twice the speed of Qi is a major benefit to using MagSafe, but it does come with some caveats.
Buckle up.This will be more technical than we usually get.If that makes you unable to read on, here's a hint: If you don't want to buy apple's USB-C AC adapter, any usB-PD 3.0 adapter of the same specification will get a faster charging rate, not a ordinary one.
USB-C PD Charger
USB PD is a specification that handles higher power on USB and allows a range of devices to charge quickly over a USB connection.It helps negotiate between the two devices so they can determine how much power they can extract from the charger PD charger offers a variety of power configurations from 5V to 20V, including the critical 2.22 ampere power configuration.More on this later.
The USB PD 3.0 specification was released in mid-2019, and the introduction of this technology will take time. Adapters bought before 2020 may not have specifications, so it will not be possible to meet MagSafe charging requirements. There is a reason why Apple chose this specification. It is a smarter standard that can learn more about the device being charged.
USB PD 2.0 devices will only negotiate power based on power requirements. The USB PD 3.0 specification allows the adapter to obtain more information from the device when charging, such as temperature and charging failure.
The USB PD 3.0 specification also includes more smart features to control amperage and voltage when charging. When adjusting the voltage or amperage, it can move in steps as low as 20mV or 50mA, and continuously adjusted by the power supply every 10 seconds.
Therefore, even though Apple could have used the older specifications in accordance with its 15W charging requirements, it decided to rely on the newer specifications to design safer and more efficient solutions. USB PD 3.0 is backward compatible, which is why even though the rated power is 96W, you can still get 10W from the old charger.
If the MagSafe disc and the AC adapter cannot negotiate 9V and 2.22 amps, USB PD charger will use the most universal mutual compatible voltage and amperage it can reach by default, but it must not exceed 9V or 2.22A. Depending on the AC adapter you are using, this will be different because the MagSafe disc can handle 9V and 2.22 amps.
Other voltages can be provided for negotiation, but cannot exceed the highest voltage "rail" required in the adapter. After the device is connected, it will negotiate with the adapter to obtain the best voltage rail combination to achieve maximum efficiency when charging.
The adapter can provide amperes of up to 5A rated current and determine the best amperage to be used in negotiation. Modern equipment chooses variable voltage and constant amperage to better control temperature. For products such as MacBook Pro, only the 20V power rail uses 5A rated power to reach 100W rated power, while the rest rely on 1.5A to 3A rated current to maintain a constant current.
As we said, Apple uses 9V and 2.2A for its MagSafe charger to reach 20W. You can only get this combination in a USB PD 3.0 20W or higher wattage adapter-Apple is not the only company offering this combination. Higher power alone will not work.
Why can't a 15W adapter get 15W out of the MagSafe charger?
Apple's 20W adapter next to Anker's 20W adapter
Many friends have questions. Why does the wireless charging manual clearly say that the maximum output is 15W, but when I charge my mobile phone, there is no 15W.
Even considering the USB PD 3.0 requirements mentioned above, no system can achieve 100% efficiency. Even if we ignore the industry specifications and build a 15W adapter for a 15W wireless charger, it cannot meet the minimum requirements for full-speed charging.
These characteristics will affect the conventional charging through the cable directly plugged into the device, so due to the loss of efficiency, a 15W adapter connected to a suitable cable will still only charge less than 15W. In fact, when charging via wired or wireless means, the heat emitted by the iPhone is generated by the chemical reaction of battery charging, which means that the charging efficiency is reduced.
Just because of the resistance of the cable itself, the efficiency of direct cable charging has been lost. A short, thick cable will have less resistance than a long, thin cable. The greater the resistance of the cable, the more energy is converted into heat. This is called copper loss and is inherent to any electrical system, just like the inherent friction of a mechanical system.
When current passes through the charging coil, various losses occur. The first is copper loss. Due to the thickness of the coil, you have to introduce more resistance, which will generate more heat. The second loss is due to the generation of a magnetic field called eddy current loss in the charging coil, which also introduces heat into the system.
The heat generated from wireless charging due to how energy is passed between charging coils represents the sheer inefficiency of wireless charging. While more convenient, assuming a constant rate of battery charge, you are using more power per minute when using MagSafe or Qi. Alternatively, using the same charger with the same power per minute, you will deliver less power to the battery wirelessly charging than when using a cable.
How to tell if the iPhone is in fast charging Speed?
- You can try to connect an ammeter to check the charging power. The charging power of different devices is slightly different. The fast charging state is usually between 13.5~18W, which is related to the remaining power of the device.
- From the perspective of charging time, in PD fast charging mode, the device can be charged to 50% of the power within 30 minutes.