Apple MagSafe Charging Speed Tested


A comparison of USB-C chargers and a USB hub when used with the Apple MagSafe wireless charging puck at different ambient temperatures. 

Steve Tyson of Cambrionix

Blog Post
December 1 |  20 min readTL;DR: Grab a PDF version here.

THE CHARGING RATES AND CAPABILITY OF  USB-C CHARGERS WHEN USED WITH APPLE MAGSAFE 


Why I’ve written this charging article…

There’s recently been some confusion across the internet with the capability of the Apple OEM USB Type-C chargers (usually referred to as just USB-C) when used with the Apple MagSafe Charger. In this post I’ll share data about how the MagSafe performs with a number of Apple USB-C chargers and a Cambrionix Type-C USB hub.

I haven’t gone into enormous depth regarding the USB Power Delivery (USB PD) protocol and what happens ‘under the hood’. This post is designed to help you make your own decisions on whether MagSafe is/isn’t for you and if the charger you already have will work effectively with it.

I’ll also explore whether its better to charge your devices in the oven or the fridge!

Too long to read right now? Download the PDF here or skip straight to the conclusion. 

Need help?

Do you need more help configuring your own solution or system to charge USB hubs? Contact us for expert USB advice and support. 

Apple MagSafe Charger 

Apple’s MagSafe Charger connects to a USB-C charger via a USB-C cable/connector and provides wireless charging capability. It’s compatible with the Qi wireless charging protocol. It supports proprietary wireless charging from Apple in order to sneak some extra power across the gap. ‘Charger’ is used loosely since both the USB-C ‘chargers’ and the ‘MagSafe Charger’ are effectively both power supplies utilising Type-C.

Battery management and charging electronics are within the iPhone itself, which is a wise move.  Charging Li-Ion batteries can be a dangerous pastime if not done correctly. Leaving a peripheral to manage the process opens up rogue peripherals to do damage to the iPhone internal battery. But enough about that, back to the MagSafe Charger.

As you expect, MagSafe is a nicely designed wireless charger which, if you have the latest  iPhone 12, holds itself in place on the rear of the phone via integrated magnetics. This ensures the wireless charging coil is placed parallel and centred with the opposing coil within the iPhone.

Fair play to Apple. This is a neat solution. It removes one of the main issues with wireless charging, poor alignment of the coils causing poor power transfer efficiency. There’s data, as well as power, transferred between the MagSafe and the iPhone 12. Although I haven’t documented the communication (made possible via NFC), it can be used to identify the MagSafe compatible accessory stuck to the phone.

Why USB-C Power Delivery?

USB-C Power Delivery (USB PD) chargers take advantage of extra control channel signals within a USB-C connector/cable, which are only accessible by using a USB-C connector and appropriate cable. These control signals allow a charger to advertise its capabilities to a device and the device to tell the charger what it will accept. Other info changes hands between the charger and device, ACK’s, vendor data etc but that’s for another day. 

USB PD 2.0 also allows for a number of different voltages and current limits to be advertised to the connected device: 5/9/15/20V, 2/3/5Amp etc. The advertised voltages depend on the power available from the charger. This power is calculated by multiplying the charger Voltage by the charger Current in Amps. For example, a charger offering 9V and 3Amps would be offering 27Watts (9×3=27).

In the case of a MagSafe Charger, it is looking for 9V at 2.22Amps which works out to be 9*2.22=20Watts. This 2.22Amps should be regarded as the minimum current that a compatible charger should offer at 9V.

All USB-C cables, according to the USB-C spec should be able to handle at least 3Amps. 5Amp cables require additional electronics in the form of an e-Marker and are designed for devices requiring over 60Watts such as some laptops. If you’ve got time on your hands and want to learn more about this then here’s a link to a presentation on USB Power Delivery from

What does MagSafe use: USB PD 2.0 or USB PD 3.0? 

During testing I captured the data packets between the USB-C charger and the MagSafe Charger. These data packets were only relating to USB Power Delivery (USB PD) spec version 2.0, rather than USB PD 3.0.

Is there a problem with this? No, although I expect to see Apple switch to USB PD 3.0 across the board in the future so they can leverage the increased functionality within the USB PD 3.0 spec. The 2018 MacBook Pro ‘talks’ USB PD 3.0.

USB PD 2.0 will work with a USB PD 3.0 charger since USB PD 3.0 is backwards compatible. Which means there are additional features baked-into USB PD 3.0, which can offer benefits: 

Wireless charging and the environment

Wireless charging will never equal the efficiency/speed of wired charging. As a result it’s the least friendly to the environment both in terms of quantity of materials used and energy wasted as heat. Calculating the inefficiencies of wireless charging and multiplying this by the number of mobile device users in the world gives a very daunting figure in terms of wasted power, albeit a worst case scenario.

My view is that MagSafe Charger will not replace having a Lightning or USB-C connector on an Apple product. If it did then ultimately, over time each and every mobile Apple product would utilise it and each and every user would waste some additional Watt-Hours each time they charge their phone. This kinda goes against the world efforts to save energy.


The tests   

How the test data was collected

The data was collected using a commonly used USB PD Analyser which measures Vbus, Vconn, CC1 and CC2 voltage and current as well as capturing and decoding the USB PD data packets between the USB-C charger and MagSafe Charger. I haven’t published the data packets between the USB-C charger and MagSafe Charger as it doesn’t help present the data which the article is about: How quickly does the MagSafe Charger charge an iPhone 12 from 0-100% with various USB-C chargers.

Collecting charging data was a long process!Firstly I have to drive the battery level of the test iPhone 12 down to the point where it doesn’t boot. This takes many hours of streaming video, sound and flashlight! Once the battery is flat, I charge it and record various parameters during the full charging run from zero to 100%. Each of the tests runs for at least 4hrs and create a CSV file with close to 2,000,000 rows! Way in excess of the amount of data which Apple Numbers and Microsoft Excel can import. Thankfully the  DataGraph for MacOS app helped dealing with huge CSV files.

Cambrionix_USB_MagSafe_USB-C_Testing


The tests

Tools and equipment used


The tests

Testing notes


The tests

Starting a charging test

The battery within the phone is deemed almost charged once the current trace curves downwards to a power level of around 1Watt. This includes power being consumed by the iPhone and the MagSafe Charger. To calculate power, multiply the current (Amps) by the voltage level which, in the case of all the USB-C chargers tested, is 9V.

Once the power level starts to creep down it’s sensible to check the phone to see what the charge level is. If it’s under 100%, keep charging. When checking the battery percent I left the phone on the MagSafe Charger and tapped power button once to see the charge level. The iPhone was not unlocked and the screen only stayed illuminated for a few seconds.

So, that’s the equipment required along with a basic test method. Let’s now take a look at the data which was captured. Oh, but first, please accept my apology to the whole internet for using the word ‘puck’ when referring to the MagSafe Charger on the graphs. I do struggle with calling it a charger and the charger it connects to also a charger. 


The test results – 

Different chargers performance

Apple 18W USB-C Charger

The first charger on the list is the Apple 18W USB-C charger.

The MagSafe Charger accepts 9V at 2Amps (18W) from the USB-C (Type-C) charger and the iPhone shows as being fully charged after 3.5hrs. Ambient temp was 22℃.

Both the MagSafe and iPhone takes ‘gulps’ of current centred around the 4,000 seconds mark. Maybe the current goes up and the iPhone monitors the change of internal temperature and cranks down the charging current if it rises?

Apple 18W USB-C Charger

Apple 20W USB-C Charger

This is the charger which is recommended for use with the MagSafe Charger. The iPhone 12 gets to 100% charged after 4hrs and the MagSafe Charger accepts 9V at 2.22Amps (20W) from the USB-C charger. Ambient temp was 22℃.

Unusual drops in charging current shown here centred around the 7,000 seconds mark.

These drops in current may be required to allow the iPhone or MagSafe Charger to cool.

Apple 20W USB-C Charger

Apple 87W USB-C Charger

iPhone 12 shows as 100% charged after 3.5hrs. MagSafe Charger accepts 9V at 3Amp (27W) from the USB-C charger. Ambient temp was 22℃. The current profile is similar to the Apple 18W USB-C charger.

Interestingly this USB-C charger advertises 5/9/20V to the MagSafe Charger. No option for 15V which is 1) Strange and 2) a possible diversion from the PD2.0 spec.

Apple 87W USB-C Charger:

Cambrionix PDSync-4 60W USB-C Charger

The iPhone shows as 100% charged after 3.7hrs and the MagSafe Charger accepts 9V at 3Amp (27W). Ambient temp was 22℃.

The current profile is similar to the Apple 20W USB-C charger.

Cambrionix test of the PD Sync USB-C Charger

Charging current profiles from all chargers

This graph shows all previous data overlaid using the same X and Y scale. It’s a little hard to interpret but it does show just how close the four USB-C chargers are in terms of operation and the race to 100%.

All USB-C chargers tested get the iPhone 12 from 0-100% within around 30mins of each other at an ambient temperature of 22℃ (the controlled temperature in my kitchen!).

Cambrionix test of all Apple USB-C Chargers


Analysing the charging test results

Initial thoughts on the data

I’m presenting basic comparison data to give a little more insight into what happens to the charging current when a MagSafe Charger is used with an Apple or non-Apple USB-C Power Delivery charger and an iPhone 12.

I don’t have detailed data regarding the decisions made within the iPhone and/or the MagSafe Charger when it comes to manipulating the battery charging speed although Apple do offer the caveat that charging speed may vary depending on System Activity and Temperature:

These caveats from Apple make perfect sense from a technical point of view for the following reasons:

What I think is going on: 

My educated guess is that there are some clever Apple algorithms which take all of the previous factors into account and either reduce or increase the charging speed in response to these environmental and system factors between the iPhone and MagSafe. I suspect these algorithms may maintain a balance between charging as fast as possible whilst maintaining battery health. As a result, I believe there is a big emphasis on temperature.

Charging in the refrigerator

In order to test the idea that temperature plays a big role in determining charging speed I performed a 0-100% test-run in a household fridge. This isn’t the most scientific test but hey, we’re all working at home right now so a kitchen-lab will have to do!

The temperature within the fridge was maintained at 3℃. In order to be sure that the door remained closed during the test, the family was packed off to bed and the test was run overnight.

Other things woth mentioning is that the phone was in the same starting-state as with the previous tests and the MagSafe and iPhone 12 both had over 2 hours within the fridge to get to temperature.

During these 2 hours the iPhone and MagSafe Charger were not powered up.

Testing Charging rate in a fridge

Here is the test run from the fridge at 3℃. along with the previous results from 22℃. The reduced temperature seems to keep the charging current, shown in red, at a higher level for longer.

Charging in the oven (don’t try this at home like I did)

Ok, so it charges better in the fridge, what about the oven?

Lets do a test run at the upper limit of Apples’ charging temperature, 35℃.

This test run performed as expected, poorly; the iPhone and MagSafe Charger had an hour to get to temperature in the oven and the 20W USB-C charger, laptop etc remained outside of the oven.

To cut a long story quite short, the iPhone 12 never reached 100% charged even after 14hrs. In fact, the phone reached 66% after approx 2.5hrs and then remained at 66% for the duration of the 14hr test run. Without knowledge of how the iPhone (or MagSafe Charger) increases/decreases charging current based upon temperature all I can speculate is that Apple are adhering to the upper 35℃ limit on battery charging ambient temperature. This is a good thing since it’s commonly known that charging in an elevated ambient is bad for batteries.

Somewhere within the recommended ambient operating range of the iPhone and MagSafe Charger there will be a Goldilocks-zone where the temperature is just right and charging is optimised. Much more testing is required in order to find this sweet-spot though.

The first graph shows the full 14 hour test run data. The second graph shows the fridge, oven and 22℃ data overlaid and trimmed to 15,000 seconds.

We suspect that some form of battery protection was being used by the iPhone due to the elevated temperature.

Charging_an_iPhone_in_an_oven...temperature charging test.

Charging_In_The_Oven


Conclusion  

The differences in the charging speeds of the various USB-C chargers is minimal and any charger offering 18W or more and supporting USB-C PD2.0 or PD3.0 should, and does, work just fine.

Does temperature have much of an effect on the MagSafe Charger+iPhone 12? Yes it does, and yes it should.

Charging your devices within the temperature range recommended by Apple will ensure you get the best performance and longevity from your battery.

Charging on a hot day in an ambient temperature of 35℃ or more makes effective and speedy charging almost impossible.

Whether this is worth clearing your beer fridge for is another matter…