Hello I am thinking about buying the APC Back-UPS ES 700VA 230V UPS. I calculated that after the upgrade from my old GTX 660ti to GTX 1060 my power usage will be about 478 W, and the recommended UPS is 900 VA according to PSU calculator. I also use two monitors with power consumption of 26.10 W (primary) and 50 Watt (secondary) and Philips 2.0 computer speakers. In case of power outage I just need my computer and primary desktop to work for about 2min to allow me to save my work and shut down the PC.

I am not sure how does it works exactly, does it mean that if I will buy 700 VA UPS and there is electricity outage, it will provide electricity for a shorter period of time (on the website they say that Typical Backup Time at Full Load is 3.9 minutes (405 Watts)), or will it not hold at all because required Wattage is too high?

  • How exactly did you calculate that you're computer will draw 500 Watts? – Hydranix Sep 28 '16 at 10:11
  • I used this site: outervision.com/power-supply-calculator, sorry I should have mentioned that before. – Pawel Sep 28 '16 at 10:15
  • Ah ok, then that's the wattage your power supply should be rated for to power your system efficiently. If you only need a 500Watt power supply, then that UPS will easily handle it. – Hydranix Sep 28 '16 at 10:18
  • Well to be exact the recommended PSU Wattage is 528 W. but I already have Corsair TX750 PSU. I presume that make no difference as the PSU will take only what it needs? – Pawel Sep 28 '16 at 10:25
  • Did you consider the requests of your Monitor too? Please edit your question adding which is the use you need from an UPS. I mean if you want that the computer turn-off (hybernate) and no more, if you need some minutes to act (monitor needed)... the answer could depend on it. – Hastur Sep 28 '16 at 12:28

Drawing more than 405W will overload this UPS model. It will then stop supplying battery power to all connected devices immediately to protect itself. The specs are present in the manual, which is available (for now) here.

The power limit is not just about battery capacity. It’s also about what the voltage converter component can do. Your computer doesn’t run on the battery’s native voltage (usually 12V) after all.

  • Could the UPS overload cause damage to my PC or UPS unit? Also from the manual I understand that if the unit is overloaded it will not provide the electricity even if not on the battery supply. did I get that right? – Pawel Sep 28 '16 at 12:20
  • It should not cause any damage. The manual says “During On Battery operation a battery power supplied outlet overload was detected.”, so I think it only applies to battery use. All non-Pro Back-UPS models are “Standby” type, where the DC/AC converter is not active when utility power is available. There’s another circuit breaker however, for the entire unit. The specs mention a maximum total current of 10 A. – Daniel B Sep 28 '16 at 12:52

When voltage is stored inside a UPS for a given Wattage, and you draw more wattage than the device is designed for, the battery will drain quicker. Keep in mind, that the more you go over the limit, the faster it drains.

So it will basically shorten the time that your UPS will be a backup, which of course is only the case when you are using your computer to the max. Even though your GPU uses a lot of power, it only does so when you are actually doing graphics intense stuff, such as gaming. When you just use normal desktop stuff, it is likely your computer does not draw 500 watt at all, and thus the UPS will not require that either.

Keep in mind, that UPSses are usually designed with a server in mind. They have a different load that is usually constant, and the wattage is usually not due to the graphics card used, but the CPU which is usually constantly active at the same wattage.

My computer has a 650 Watt PSU, but I've hooked up a meter to get a readout of what it really uses when I use the computer normally, and thats about 280 Watts. But when I start a game, it shoots up to 450 easily and higher when the graphics intense stuff comes.


I have that same UPS (albeit an older version with US sockets).

That UPS will be enough to give your computer the time it needs to shut down.

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