iMac USB-C giving only 500 mA?

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iMac USB-C giving only 500 mA?

I though all Mac USB-C ports should give at least 900 mA but my iMac (Retina 4K, 21.5-inch, 2017) is giving only 500 mA to my external drive (Samsung T5) that requires 896 mA.

When plugging drive to USB-A port it gives 900 mA which is enough but I'd like to use USB-C to free up USB-A ports.

I've installed all the latest High Sierra updates to iMac.

Is this some kind of firmware bug or is the IO of new iMacs just badly build (since 2012 MacBook Pro can give 1100 mA)?

iMac 21.5" 4K, macOS 10.13

Posted on Apr 7, 2019 4:48 AM

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Answer 1

den.thed

Level 10

95,740 points

Apr 7, 2019 7:19 AM in response to henkkapple

Where do you see or read that the T5 requires 896 mA. Does the T5 work when you use the supplied Samsung USB-C to USB-C cable?

If it does, then just plug it into a USB-C port and forget about it.

If it does not, then get a USB 3.0 hub and expand the number of USB-A ports.

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Answer 2

henkkapple Author

Level 1

5 points

Apr 14, 2019 2:50 AM in response to henkkapple

Turns out USB cable was broken on EVO 860 and iMac was more picky about the cable than Mac laptops. I still don't understand why T5 gets only 500 mA using USB-C.

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Answer 3

henkkapple Author

Level 1

5 points

Apr 13, 2019 10:28 PM in response to henkkapple

More information

When I plug Samsung T5 on USB-A it says USB 3.0 and iMac gives 900 mA. When I plug it to USB-C it says USB 3.1 and iMac gives 500 mA.

Today I noticed that my other external SSD (Evo 860 on usb-powered dock) is not showing up anymore on iMac if I connect it straight to USB-A. It still connects if I'm using Usb power 3.0 hub and it connect without any problem to Macbook pros and MacBooks. There's something weird going on my iMac.

I tried SMC-reset but it didn't help.

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Answer 4

henkkapple Author

Level 1

5 points

Apr 7, 2019 8:58 AM in response to den.thed

The information I found was under System information / system report / USB. I'm using original cables supplied by Samsung.

Samsung T5 work but it becomes sometimes slow when doing for example photo editing though cpu usage is low. So I suspect lack of power is making T5 slow.

I remembered wrong about MacBook Pro (2012) ports. They were 900 mA not 1100 mA.

USB-C should be 900 mA accoring this Apple site: https://support.apple.com/et-ee/HT201163

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iMac USB-C giving only 500 mA?

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