UPS + PSU not compatible?

[Se7enLC]

I have an "old" UPS (APC 1000VA model BR1000G, stepped sinewave). I upgraded my machine, including a Thermaltake ToughPower 750W Gold PSU (https://www.thermaltakeusa.com/toughpower-grand-rgb-750w-gold-full-modular.html). The UPS is no longer able to keep the machine running when I unplug the UPS. SInce it was a few years old, I first tried to replace the batteries. That didn't change it.

 

I then upgraded the UPS to one that does "pure sinewave" and claims to be PFC compatible. Also 1500VA (CyberPower CP1500PFCLCD). This one ALSO can't keep the machine running when unplugged.

 

Are there some compatibility issues where some PSUs don't play nicely with UPS? I don't want to just keep throwing money at the problem. Any suggestions? Perhaps a known good PSU list?

[Lurick]

I know this is going to be a stupid question but are you sure you plugged into the grey/white outlet on the Cyberpower one? Only the grey/white outlets are on battery.

[Se7enLC]

3 hours ago, Lurick said:

I know this is going to be a stupid question but are you sure you plugged into the grey/white outlet on the Cyberpower one? Only the grey/white outlets are on battery.

Not a dumb question at all, thanks for the reply. I just double checked, and yes - I'm plugged into the grey+white outlets labeled "Surge+Battery". With the computer powered up at idle, I see estimated run time of 40 minutes. When I launch a benchmark, that number drops to around 14 minutes as the CPU+GPU spin up.

 

But when I unplug the UPS the computer powers off immediately.

 

[Se7enLC]

Found some pretty damning evidence on the Tom's Hardware review for the PSU (750W and 850W versions).

 

Thermaltake ToughPower GRAND RGB 850W

 

Quote

We measured a hold-up time of less than 17ms, and the power-good signal doesn't satisfy the ATX specification's required 16ms. At least it's accurate.

 

Thermaltake ToughPower GRAND RGB 750W

 

Quote

The hold-up time we measured exceeds 17ms, but the power-good signal lasts for less than 16ms. We'll still give the TPG-0750F-R a pass since its power-good signal is accurate and only a hair away from the ATX specification's minimum duration.

 

I bought a Corsair RM850X and it works just fine, I get something like 30-40 minutes of runtime on the 1500VA supply at idle. Tom's Hardware says this PSU has a Holdup time of 30 ms (vs 18 ms and 16 ms for Thermaltake) and Power loss to PWR_OK falling edge of 21.1 ms (compared to 15.88 ms and 13.9 ms).

 

Corsair RM850X White

 

And some details about how they measure holdup time: https://www.tomshardware.com/reviews/how-we-test-psu,4042-6.html

 

I'm not 100% sure this was the cause, but replacing the otherwise-brand-new-and-fully-functional PSU with a different one fixed the problem.

[Guest]

If the hold up time of the PSU time is less than the switch over time of the UPS, then yes.  The UPS is useless.