TL;DR: The UltraFine 5K seems to provide less power than the Apple 87W USB-C power adapter, as reported earlier this year by users claiming that their MacBook Pros were dying in the middle of intense tasks unless connected to the Apple adapter, but there are a lot of complexities in drawing conclusions...
A while ago, an issue was discussed after being raised by YouTuber MKBHD. He said that his MacBook Pro was discharging while connected to an UltraFine 5K display, and that he had heard the display provided only around 62W of power, compared with the 85W it is supposed to provide. He had to use the Apple 87W USB-C power adapter to avoid his Pro shutting down due to a drained battery in the middle of exporting a video from Final Cut Pro.
At the time, I suggested a method of testing whether this is truly the case (especially considering he was provided with a pre-release unit, which I speculated may not have been fully retail-ready):
If you find yourself at a loose end for 20 minutes and fancy investigating it, you could run your MacBook to a state of medium-low charge (anything under 70%) and increase the power consumption to the absolute maximum by simultaneously thrashing it with:
- four instances of the yes command in Terminal
- GpuTest's stress test
- brightness on maximum
And use coconutBattery to compare the "charging with" figure under the LG 5K charger, and the Apple charger, to see if the Apple charger shows a higher charging current (or, if Marques is to be believed, a lower discharge current).
No-one took up the offer, and I did not have the equipment to do it myself, despite encouragement...
Do it and report back to us please Brookzy
However I am pleased to report I recently took delivery of two UltraFine 5Ks, and will soon have a specced-out 15" MacBook Pro, too. That won't be here until Monday, however - despite Apple saying it will be here today
- but I do have in my hands a base model 15" Pro that I am borrowing from a friend.
Time to do some testing!
I figured it would be unwise to assume that the Thunderbolt 3 cable provided by LG is not the culprit. So my testing was done with both the LG cable, and a CalDigit 100W Thunderbolt 3 cable that I ordered specially for this test.
I had issues with GpuTest, so I used Cinebench instead. Combined with eight instances of the
yes command
("eight?!" I hear you say... "hyperthreading" I reply!) the maximum power draw I could muster was an indicated 77W, as measured in coconutBattery.
It is important to emphasise that there is no universal measure of power consumption provided my macOS. Thus coconutBattery is estimating it, based upon the power draw of key components. It is reasonable to assume, then, that the actual total drain is higher. Nonetheless, this indicator is sufficient for making comparisons.
Test #1: UltraFine 5K + LG Thunderbolt 3 cable
The battery just managed to stay afloat with low single-digit charging rates of between 0.5W and 4W. MacOS sporadically reported "Battery Not Charging", though this was inconsistent. Clearly, the UltraFine 5K
is capable of providing more than 62W - the amount cited by MKBHD - but it wasn't providing a full 85W.
Test #2: UltraFine 5K + CalDigit Thunderbolt 3 cable
The results were essentially identical to with the OEM cable. I thought at first it was providing more power, since macOS was
not reporting "Battery Not Charging" like it sometimes was with the LG cable, however I think there are too many variables to draw a conclusion.
Test #3: No display; Apple USB-C power adapter + CalDigit Thunderbolt 3 cable
Now we see concerning results: the charging capability increased using the Apple charger - reaching more than 10W for some periods.
Interpreting these results
The Apple power adapter seems to provide more power than the UltraFine 5K, however this test is not enough to reach the conclusion that the UltraFine 5K cannot provide 85W for the simple (though easily missed) reason that despite my best efforts I
could not get the battery to drain whilst plugged in to the UltraFine 5K.
This is important because of the complexity of the electronics in these devices, which we know "negotiate" power supply and demand based upon the USB-C specification.
It seems to me that the Apple power adapter is in 'full speed' mode (if you will) at all times, whereas the UltraFine 5K defaults to a more casual 60W-ish of provision unless more is required.
Next steps
The goal is to try to get the MacBook Pro to drain power whilst connected to the display. When I get my higher specced machine next week, I will re-test to see if I can get more power consumption. I'm open to suggestions of how I can increase the power consumption further!
If it is not possible to make it drain, then we can reasonably conclude that the YouTuber's display was defective, and that a different style of power negotiation is in use.
