connected pc or server hard reboots after reconnect on AC power of UPS Pro 550VA

[Anonymous user]

I recently bought a back-up UPS 550VA for my home server. I also tested with my home PC (not connected simultaniously of course) and both machines draw between 30 and 120 Watts during testing. With powerchute home edition both my home pc and server complete a shutdown (hibernation disabled) 1 minute after I pull the AC plug from the UPS, which is what I set powerchute to do. About 1/2-1 minute after I reinsert the AC plug into the UPS, it makes a clicking sound and the display indicates it's back charging on AC power. I understand this delay is how it's meant to behave, but not sure. Thereafter i simply power on the pc or home server and everythings fine.

Also, when pull the AC plug only for a short time with either PC/server running and reinsert the AC plug before shutdown the unit instantly switches back and forth between AC power and battery. Here there's no delay.

However, if I set either PC/server to restart on AC reconnect (from BIOS) or enable hibernation i get an odd behaviour. Both PC and home server shut down or hibernate after beforementioned 1 minute nicely after unplugging the UPS. If I then reinsert the AC plug into the UPS either PC/server restart or wake from hibernation. The tricky part is, on AC plug reconnection the UPS keeps running on battery for about a minute and then clicks and switches to AC power. At that point however both the pc and server experience a hard reboot just after powering up, as if losing power momentarily.

Is this hard reboot faulty behaviour or am I missing something?

Home PC: Intel I5 4690K with IGP and two SSD's and a Seasonic G-series 360W PSU

Home server: Intel I5 2400K with IGP, four 3,5" drives, a 2,5" drive and a CoolerMaster V-series 450W PSU

[voidstar_apc]

It sounds like your PC detects the AC being plugged back in and wakes up too soon. Try using a power strip to switch the AC to the UPS on and off. That keeps the ground connected.

[Anonymous user]

So why does the UPS take a full 1/2-1 minute to detect the AC being plugged in then? It only does that when the pc has been powered down and when the switch to AC occurs the system is already up and running. Can it be the caps in the UPS or PSU aren't fully charged yet causing the switch to AC to fail.

[voidstar_apc]

When your PC decides to shut down, the UPS needs to wait for shutdown to complete (usually two minutes) before cutting power to the PC. Even if power returns, the UPS needs to complete this process to ensure the PC finishes its safe shutdown, detects loss of power and then turns back on. In you case, it seems like your PC turned back on early before the UPS cut power. One possible cause for this is the ground connection which is why I recommend testing with a surge strip.

[Anonymous user]

Today I got around to testing with a surge strip but it does not seem to make a difference.

I definately saw/heard the UPS cut the power two minutes after shutdown. After flipping the switch on the surge strip the pc again turns on and boots up. The UPS however starts making the clicking noise about a minute after flipping the surge strip switch, en then the hard reboot occurs.

If I disable auto startup on the PC though, having waited the two minutes for the UPS to cut power, after I flip the surge strip switch the UPC clicks instantly. I then turn the pc on with the on switch and everything boots fine, no hard reboots.

At this point i'm assuming its got something to do with compatibility with my active PFC PSU's and giving up on the auto startup. In the Netherlands power outages aren't that numerous so I can suffer flipping a switch manually. Just seems it should be able to work. Also I'm hoping it's not a faulty UPS. Seems a bit minor thing to RMA the unit.

[voidstar_apc]

Interesting. So if I understand correctly the timeline without auto-power-on is:

1) PC shuts down

2) 2 minutes later UPS turns off

3) AC re-established

4) Power immediately restored. PC can be turned on manually.

And with auto-power on

1) PC shuts down

2) 2 minutes later UPS turns off

3) AC re-established

4) Power immediately restored. PC turns itself back on

5) One minute later UPS starts clicking and PC hard reboots.

I'm not sure how to explain that. Although the PSU exceeds the UPS' wattage rating, I would expect any PSU problems to affect both cases (with and without auto-power-on). And from what you're saying it sounds like the hard reboot occurs well after the UPS restores power.

[Anonymous user]

Almost correctly:

With auto-power on

1) PC shuts down

2) 2 minutes later UPS turns off

3) AC re-established

4) Power immediately restored. PC turns itself back on but the UPS's display says it's still on battery power.

5) One minute later UPS starts clicking and PC hard reboots. At this time the UPS's display states it switched to AC power

Do you really think the UPS' power rating might play a role? I had a power meter on both systems that says it doesn't peak over 150Watts on boot.

[voidstar_apc]

The UPS' power rating sometimes plays a role in UPS and PSU compatibility, however your PSU and UPS seem to be working well together.

On 3/7/2017 11:49 AM, Bart said:

4) Power immediately restored. PC turns itself back on but the UPS's display says it's still on battery power.

5) One minute later UPS starts clicking and PC hard reboots. At this time the UPS's display states it switched to AC power

Okay, that's what I originally thought was happening. We want the PC to turn on during step (5) after the UPS stops providing power and then switches back to AC. Instead it's turning on early at step (4) when the UPS is still providing battery power. The PSU is somehow sensing the change in AC and turned the computer back on. Since you used a power strip for testing, it's probably not sensing the ground line being broken/reconnected.

If that interpretation is correct, then if you waited until the UPS turns off power before re-applying AC, then the computer would not hard reboot since it wouldn't turn on prematurely. However real power outages cannot be relied on to be so courteous.

The only other thing I can think of is try disconnecting USB devices and try having the monitor attached to the battery backed outlet to make sure no electricity flows to the PSU that way.

[voidstar_apc · Accepted solution]

I took a closer look at the timeline.

You're saying the UPS turned off in step 2 (no longer on battery), turned back on in step 4 (on battery), and then turned off again in step 5? One way to tell if the UPS is on or off is to put a night light into one of the battery backed outlets.