Igor Kromin |   Consultant. Coder. Blogger. Tinkerer. Gamer.

I've noticed a while back whenever I was charging my 2017 MacBook Pro via the left-hand side USB-C ports that it would get quite hot, even if I wasn't doing any CPU intensive work. However, while charging via the right-hand ports it remained cool. I've finally got around to measuring this and here are my results.

At the start of each test I let the MBP run down to 80% charge and then cool down for 5 minutes in the outside 18C temperature to bring it down to around 28C chassis operating temperature. Then I plugged the USB-C charge cable in and let it charge back up to 85% charge while monitoring its temperature.
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Here are the results of temperature readings at the 85% charge level. I monitored these further and they didn't fluctuate much from this so I think that is a good representative temperature for comparison purposes.

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Left-hand port charging was considerably hotter internally (54C vs 30C) than right-hand port charging. Current draw was around the same in both cases, certainly not enough to affect this huge temperature difference. That leads me to think that I either have a defective left-hand port charge circuit or the circuitry on that side is less efficient.

I also measured chassis temperature (with a laser thermometer) above the touch bar - left, centre and right. Since I'm in Australia I thought it would be fun to use the same temperature scale as used by the BOM to illustrate the differences in temperature...
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The chassis temperature differed by only 6C but it was still quite a noticeable difference.

These tests were done while the MBP was idle. When I was doing some work and charging via the left-hand port I noticed that the fans would go into overdrive, while right-hand charging didn't have the same effect. This is unfortunate because it means I have to have the power cable across my mousemat whenever I'm working on the road if I want to avoid the Mac heating up so much.

-i

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