"Smart" power strips and the iMac

camner

macrumors regular
Original poster
Jun 19, 2009
140
0
For years with a Mac Pro I used a "smart" power strip (the kind that has a "control" outlet that one plugs a computer into, which when it senses that the computer is asleep or off shuts of power to the other outlets into which one plugs peripherals such as one or more monitors, powered USB hubs, etc).

I recently purchased a late 2015 iMac, and I'm finding that there seems to be some kind of "feedback loop" that prevents the iMac from staying asleep when used with the smart power strip.

For example, I plugged a second monitor (connected via a Mini DisplayPort cable into a Thunderbolt port) into one of the "slave" outlets on the smart power strip. When I put the iMac to sleep, the iMac goes to sleep, and the smart strip dutifully shuts off power to the second monitor. Then, about two seconds later, the iMac wakes up on its own. If the second monitor is NOT plugged into a "smart strip," then the iMac sleeps (and stays asleep, as it should).

The same thing happens with a powered USB hub, or any external drive, connected either via Thunderbolt or USB.

The only peripherals that seem NOT to induce the iMac to spontaneously wake up after about 2 seconds are my external speakers (plugged into the headphone jack) and a wireless mic receiver plugged into a USB port (directly into the iMac).

What's going on here? Is there a fix/workaround? It would be nice not to have all that "phantom" power being used, if possible.
 

ApfelKuchen

macrumors 68040
Aug 28, 2012
3,666
2,268
Between the coasts
Not sure where the apparent feedback loop would be (never used a smart power strip), but here are a few ways to try to isolate it.

1) System Preferences > Energy Saver > Wake for network access - on, or off?
2) Disconnect the second monitor's Mini DisplayPort cable, but leave it connected to power.
3) Can the control outlet's sensitivity be calibrated/adjusted? The iMac uses substantially less power than a Mac Pro, which may have an impact on when it switches off/on.

I'm figuring the iMac's power supply is not sensing activity or importing control signals via the power cable. It seems more likely that when one or more of your external devices shut down, they're sending a signal (perhaps a spurious pulse) via USB or Thunderbolt back to the iMac that the iMac interprets as a wake-up call.
 

camner

macrumors regular
Original poster
Jun 19, 2009
140
0
Rather than a power strip which will provide extremely little (read no) protection, consider an uninterrupted power supply (UPS).
To simplify the question, I didn't mention that I have a UPS and the smart power strip is connected to the load side of the UPS. Thanks for the suggestion.
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Not sure where the apparent feedback loop would be (never used a smart power strip), but here are a few ways to try to isolate it.

1) System Preferences > Energy Saver > Wake for network access - on, or off?
Wake for network access is off, as is power nap.
2) Disconnect the second monitor's Mini DisplayPort cable, but leave it connected to power.
If the signal cable is disconnected, the iMac does not spontaneously awake.
3) Can the control outlet's sensitivity be calibrated/adjusted? The iMac uses substantially less power than a Mac Pro, which may have an impact on when it switches off/on.
Yes, the sensitivity can be adjusted, and needed to be, for just the reason you outline. The threshold had to be set lower. But I don't think that's related to the problem of the undesired awakening. When the iMac is asleep, it obviously still is "on" in some sense, because it notices a key press to wake it up. I'm thinking your theory below (about the spurious signal) is probably what is happening.
I'm figuring the iMac's power supply is not sensing activity or importing control signals via the power cable. It seems more likely that when one or more of your external devices shut down, they're sending a signal (perhaps a spurious pulse) via USB or Thunderbolt back to the iMac that the iMac interprets as a wake-up call.
 

Fishrrman

macrumors Core
Feb 20, 2009
19,634
6,841
Is it possible to disable the "smart features" of the power strip, and just "reach down to the power button" and use it manually?

And try this method for a day or two?
 

camner

macrumors regular
Original poster
Jun 19, 2009
140
0
Is it possible to disable the "smart features" of the power strip, and just "reach down to the power button" and use it manually?

And try this method for a day or two?
Well, in essence I've already done this. Because I don't want my iMac to stay awake all the time, I've taken the items that were causing the spontaneous awakening and plugged them into a "dumb" outlet. That fixes the spontaneous awake problem, but now I either have to keep those items on or turn them off manually each time I leave my machine, which is a pain. That's what the smart strip is supposed to take care of by itself!
 
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