Weird iMac behavior when plugged into a UPS

[darkaxe201]

My iMac (Retina 5K, 27-inch, 2017) seems to exhibit this behavior when plugged into my APC UPS (BVX900LI-MS).

iMac turns on in this scenario:

1. ⁠Plugging the UPS to the wall outlet
2. ⁠Turning the UPS on
3. ⁠Plugging the iMac into the UPS

iMac fails to start in these two scenarios:

1. ⁠Plugging the iMac into the UPS
2. ⁠Plugging the UPS to the wall outlet
3. ⁠Turning the UPS on


1. ⁠Plugging the UPS to the wall outlet
2. ⁠Plugging the iMac into the UPS
3. ⁠Turning the UPS on

Any idea on why this happens?

 

[JJayguy23]

My iMac (Retina 5K, 27-inch, 2017) seems to exhibit this behavior when plugged into my APC UPS (BVX900LI-MS).

iMac turns on in this scenario:

1. ⁠Plugging the UPS to the wall outlet
2. ⁠Turning the UPS on
3. ⁠Plugging the iMac into the UPS

iMac fails to start in these two scenarios:

1. ⁠Plugging the iMac into the UPS
2. ⁠Plugging the UPS to the wall outlet
3. ⁠Turning the UPS on


1. ⁠Plugging the UPS to the wall outlet
2. ⁠Plugging the iMac into the UPS
3. ⁠Turning the UPS on

Any idea on why this happens?

Is the UPS also connected via USB to the iMac? How old is the UPS?

Sounds like a voltage, hardware or firmware issue on the UPS. My guess is the UPS cannot handle the load of turning on, and starting the iMac at the same time. Try a new UPS. The UPS motherboard might be dying.

 

[liontamer67]

I have had this problem also since last year. Enough that I didn't even consider it was my new UPS causing problems. I paid to have my 27" 2019 retina 5K also.

So I had asked and someone said the iMac is a workhorse and the UPS likes to take breaks and it was causing my iMac to freeze and reboot itself. Mind you I also had more outlets and hired electric company to add in more electricity to my house.

My UPS is from Costco and I purchased a new one from last year as I thought maybe it was my old UPS (same brand but older).

Now I have my iMac plugged into the wall and not UPS. My old 27" that I upgraded and gave to my dad never had one problem with the UPS. So it is for sure something to do with Mac.

I redid my desk area since I painted. Now I am plugging in my external harddrives to the UPS and both connected to the back of my iMac and guess what? It froze and restarted. I unplugged both external harddrives and it restarted with no problems.

Seriously I have ZERO idea why it's doing this!

 

[harriska2]

Part of our house is on UPS and our Macs (imac, 2018 mini, 2021 MBP) are all plugged into powerstrips that are plugged into the wall that originate from the Magnum inverter. It's been that way for a decade and we've had no issues with our computers. Granted, the inverter (which acts as a UPS) cost $2600, is pure sine wave, and made in the USA. Our last one was a $900 Trip Lite and it lasted all of 13 months. You get what you pay for.