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I have my MacBook plugged into an LG Ultrafine 4K display (as recommended, sold and partially engineered by Apple).

When I unplug my Mac from it the USB hub stops charging devices attached to it. This is ridiculous as I mainly use it as a charging hub.

There is nothing in the manual about this - and I can find nothing on Google.

Is there any way to keep the USB hub powered all the time?

  • When you say _or the screen goes off _ do you mean it's gone to sleep, is on standby, or that it's powered off? – Monomeeth May 20 '17 at 8:02
  • I've rephrased the question - it doesn't matter. When I unplug my monitor from my computer it stops charging USB devices. I want to keep charging those devices. – niico May 21 '17 at 10:44
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This is expected behavior. According the LG specifications the maximum power supplied when in sleep mode is 1.2W and when off is .5W. (This is for the monitor as a whole, not just the USB ports. For this answer, let's assume all of the power is being redirected to the ports - for illustrative purposes only)

Using the formula for watts and converting to solve for Amps,

W = V * A  => A = W ÷ V

So, assuming that the 5V remains constant, the amps it's supplying is .24A in sleep and .1A off. For the record, that's not enough to charge a Nokia 3310 from 2000 much less a smartphone from the last 10 years.

The power requirement for USB 2.0 is to supply upto 500mA (.5A), 3A for USB 3.1 and up to 5A for power delivery (the type C interface).

When you unplug your MacBook from the monitor, it goes into sleep mode and dropping power consumption which ultimately disconnects your devices.

My solution is to purchase an Anker USB charging hub that's designed for this type of task. I've purchased this exact charging hub and positioned it at the side of my desk to charge the myriad of devices. Even when I need to connect my device to my Mac and charge simultaneously, I have a hub that's capable of delivering 10W on the port.

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It charge my devices nicely without a connected MacBook, if I am not using a USB-C to USB-C cable. I am using either

  • official USB-C to lightning cale
  • USB-C to micro USB cable, with micro-USB(female) to lightning/USB-C(male) adapter

If I connect a device via a USB-C to USB-C cable, things just go mess.

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