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Is it safe to use a UPS designed for desktop PCs to power a server? [Resolved]

I am working on a server within my office. The server will eventually be relocated to a data center. I would like to be able to leave the server switched on in my office, which means I would like to be able to protect it from power outages or surges. In the office I only have desktop UPSs. I would like to avoid forking out for an expensive server class UPS.

I don't mind if it only has protection for a short time (Even a few minutes would be longer than any likely power drop where I live)

The UPS is APC Back-UPS ES 400 (400 VA, 240 Watts)

The server is DL 360p Gen 8 (750 watt PSUs)

Edit Comprehensively answered. Thankyou. I will probably just leave the server switched off when I'm not there, and get it moved to the DC as soon as I can.

Asked April 21, 2017
Posted Under: Network
4 Answers

I would not plug a server with a power supply capable of drawing 750 watts into a UPS which is only rated at 240.

The issue isn't really that it's a "server" or "desktop" UPS. You're likely to trigger overload protection and drop your server even if the power input is fine.

Answered April 21, 2017

Back-UPS is not suitable for server protection. More or less suitable is the smart-UPS that has a way more sophisticated controller inside. The typical operation cycle for a power supply when the wall power goes out is:

  • If the remaining charge less than 30% the UPS sends a signal to the server to shut down.
  • The server correctly exits all the programs and sends a signal to the UPS "Be ready in 5 minutes" and runs the shutdown command.
  • UPS waits for 5 minutes and powers off the outlet the server is connected to.
  • UPS waits until wall power comes back and starts the battery charging until it is charged to 50%
  • UPS powers on the outlet the server is connected to
  • Server boots and sends a message to the UPS "I'm ready". Until now UPS does not power off the server under any circumstances.
  • If another outage happens during server startup, UPS sends the shutdown command immediately after the "I'm ready" signal is received.
  • Otherwise UPS continues charging
  • The end

Dumb back-UPSs can't do all those tricks.

Answered April 21, 2017
Back-UPS is good enough for PC that powered off manually by owner when UPS beeps and powered on when outage ends. That is his primary function. As far as server should operate autonomously, it should be powered on and off automatically and accordingly to some strategy. It's obvious that data on the server is more valuable than one on the personal computer. – Kondybas 31 secs ago
 CanDoerz  1 week ago
Is Back-UPS suitable for anything? I've used some for network devices and they have ironically caused more power outages than the environment... ;) – Esa Jokinen 5 mins ago
 CanDoerz  1 week ago

Your UPS provides power when the utility mains drops, and protects from transient under and over voltage/current conditions.

Given you can plug a desktop or a server or a UPS into the same supply socket, the power is all the same, and what comes out of the UPS is the same.

However the UPS wattage and the PSU ratings are a maximum

You need to know how much power your server draws on each PSU. You can find this information with a Watt Meter ("kill-a-watt" is one brand) or an AC clamp meter, or in your case a good estimate comes from the iLO.

iLO4 power meter image from a HP DL380 (do note my server is off at this time so the graphs are faked up) (will provide better image in a few hours)

The arrowed figure will show you a number in watts, and if its over 240W then your UPS will probably shut down with "OVERLOAD" if the mains goes out, or if the UPS needs to buck or boost.

If your draw is smaller than 240W you might get 10-30 seconds power out of the UPS. Not really enough time for a safe shutdown assuming you're standing right there.

The backUPS may or may not have a serial or USB port for monitoring, so without that and the powerchute or NUT or apcupsd software, then the server will be going down hard anyway.

Finally you might be buying yourself additional problems. If the power goes out, your UPS will do something, and run itself flat very quickly. Many UPSs will not power on when mains returns, because its better to stay off than to start up with a flat battery and be vulnerable until the charge rises. So a small power blip means you have to go into work to turn the UPS on afterwards.

tl;dr In short, that UPS is probably too small, but do check first.

Answered April 21, 2017

If the features Kondybas mentions are not required - yes, IF a) the power rating is enough (which is not the case here) and b) there is no regulatory requirement that would forbid using desktop-grade equipment unattended 24/7 - doing so could, depending on locality, violate eg fire insurance requirements or other safety policies. Also, in case of an accident, not meeting condition a) could be interpreted against you as intentionally/negligently overloading electrical equipment...

Answered April 21, 2017
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