When are USB ports powered?

millerrh

macrumors 6502
Original poster
Sep 14, 2005
460
31
just got a new iMac and loving it, but there is one thing that is bothering me. I typically leave my iPad on a stand next to my monitor plugged in to keep it topped off on battery. With my old Thunderbolt Display this seemed to work fine, but I am noticing that when I come home from work, my iPad only has about 70% battery from just sitting there. My guess is that the USB ports are not providing power whenever the iMac goes to sleep. Am I correct about that? Is there any way to successfully charge a device that is plugged in when you leave your iMac for awhile and it falls asleep? Is the powered poet behavior documented anywhere?
 

millerrh

macrumors 6502
Original poster
Sep 14, 2005
460
31
Spot on.
Same with a Magic Trackpad ~ sleep stops sending power to Trackpad battery. The Magic Mouse 2 will charge during saleep, so must be related to the power drawn from the port . You can get around this. Read this post and 'All Replies' from Apple Dioscussions:-


https://discussions.apple.com/thread/7454065
That article seems to be talking about a different thing. Which action are you referring to? Resetting SMC/PRAM?
[doublepost=1554262673][/doublepost]I did find this:

https://support.apple.com/en-us/HT204377

It seems to indicate that power should be available during sleep. So I'm not sure what is going on.
 

macduke

macrumors G4
Jun 27, 2007
10,571
14,064
Central U.S.
Weird. I have an Anker wireless charging pad on the foot of my iMac plugged into the back of it that I use to keep my new AirPods charged. I just put it to sleep and waited about five minutes, put my iPhone on the pad and it started charging immediately.
 

millerrh

macrumors 6502
Original poster
Sep 14, 2005
460
31
Weird. I have an Anker wireless charging pad on the foot of my iMac plugged into the back of it that I use to keep my new AirPods charged. I just put it to sleep and waited about five minutes, put my iPhone on the pad and it started charging immediately.
Yeah, I ran a similar test. Put my computer to sleep, waited a bit, and tapped my iPad and it showed a green charging icon working like it should. So maybe something that happens after a longer period of being asleep? I am going to leave this plugged in overnight and see what it looks like in the morning as another test.
 

macduke

macrumors G4
Jun 27, 2007
10,571
14,064
Central U.S.
Yeah, I ran a similar test. Put my computer to sleep, waited a bit, and tapped my iPad and it showed a green charging icon working like it should. So maybe something that happens after a longer period of being asleep? I am going to leave this plugged in overnight and see what it looks like in the morning as another test.
Did you restore your iMac from a backup? I did fresh start on mine. If so it could be some weird setting or corrupted file.

As a last resort you should be able to check the box "Prevent computer from sleeping automatically when the display is off" and you can at least save power on the display sleeping even if the rest of the computer is active in the background.

Also I think the SMC reset might do something with what things are working while sleeping. It kind of handles those lower level tasks, but I don't know off the top of my head if it for sure relates to this. Worth googling about that.
 

cynics

macrumors G4
Jan 8, 2012
11,334
1,709
That article seems to be talking about a different thing. Which action are you referring to? Resetting SMC/PRAM?
[doublepost=1554262673][/doublepost]I did find this:

https://support.apple.com/en-us/HT204377

It seems to indicate that power should be available during sleep. So I'm not sure what is going on.
Ahh it says it but you missed it....

Screen Shot 2019-04-03 at 6.05.45 AM.png


500 mA is standard USB charging power. If a device that requires more power to fully charge (IPAD) then you'll only get it when it's awake.

500 mA will charge an iPad but generally not all the way up and it will do it very slow. This is why the wall wart that comes with the iPad is so much larger than the one that comes with the iPhone.

Again like I said, it will charge, just not well.

500mA USB Hub,

IMG_6137.JPG

2000mA charging station,

IMG_6139.JPG

I couldn't directly test it into the iMac because it didn't like the USB tester for some reason. However volts x amps = watts. 5v x .5A (500mA) = 2.5w, 5v x 1.1A (1100mA) = 5.5A. My USB charging station is maxed so voltage is dropping a bit.

You can get a USB Hub for the mac with external power for charging.
 

StellarVixen

macrumors 68020
Mar 1, 2018
2,176
3,451
Earth
I have the RGB lit mouse connected to my MBP, and it stays lit all the time, the only exception is when the Mac is turned off.


So, the USB ports on my Mac receive power all time it seems. It probably varies from model to model.
 

millerrh

macrumors 6502
Original poster
Sep 14, 2005
460
31
You’d think even with small current it would at least trickle charge and keep it topped off.

Went in this morning, tapped the iPad, and saw no green charging light and 95% battery. So definitely was not charging even with 500mA.

I then unplugged and plugged the cable and it started charging without waking up my iMac.

Maybe it’s an issue with the cable. I am using a generic USB A to USB C I bought since my old computer didn’t have USB C ports. But now that I have them I can try the USB C to USB C cable that came with the iPad Pro and see if that changes anything.

Aside from that, might also pick up a powered hub. Been meaning to get a USB 3 hub anyway.

 

millerrh

macrumors 6502
Original poster
Sep 14, 2005
460
31
So I have ran some more tests and I think it is my cable. I noticed something strange within the System Information App. Check this out...

The cable I am having problems with is a random one I bought that is USB A to USB C. When I look at it in System Information, it is saying Speed: Up to 5 Gb/sec, Current Available: 900 mA, Current Required: 896 mA


However, when using the Apple supplied USB C to USB C cable and also another USB A to USB C cable I have, the speed is limited to up to 480 Mb/sec and the Current draw is only 500 mA. And these cables charge during sleep like I would expect .


So now I'm thinking something about this particular cable is causing the required power draw to be higher than is available in sleep mode so it just turns off the port or something. Anyone know what might be going on here?
 

curmudgeonette

macrumors 6502a
Jan 28, 2016
505
325
California
My guess is that the USB ports are not providing power whenever the iMac goes to sleep.
Newer version of MacOS (or maybe just newer hardware?) have a hibernate feature. My 2017 iMac switches from sleep to hibernation somewhere about 6 to 8 hours after entering sleep. During sleep, I can wake the computer via a wired keyboard. In hibernation, USB power is off, and hence the keyboard is off, so I need to wake the machine using the power button.
 

millerrh

macrumors 6502
Original poster
Sep 14, 2005
460
31
I spoke too soon about the other USB A to USB C cable with the lower charge current working. It does not work. I actually was in the Apple store yesterday and asked someone about this. Their hypothesis is that since it is not a cable provided by Apple, it assumes it is some third party accessory and shuts off power during sleep.

And that sort of makes sense because on a few occasions, there has been a message on my iPad saying I need to unlock it to use this third party accessory that it sensed was plugged into it.

This is rather annoying because Apple doesn't even make a USB A to USB C cable if I wanted to use one.

It's also interesting that my old 2013 MacBook Pro hooked up via Thunderbolt display didn't have this issue when the iPad Pro was hooked up via the ports on the back of the display. Maybe something about the new iMacs has a chip that senses Apple Certified accessories/cables that the old Macbook Pros didn't. Or the hub nature of the Thunderbolt display broke that handshaking.

Guess I will be using the USB C to USB C cable that shipped with the iPad Pro and look at buying a powered USB 3.0 hub as well.