Need a UPS to keep my PC running for 3 hours

I have an i3 PC.  It has a 400W psu, 22 inch LED screen, and 120 GB SSD.

Will a 3000 VA UPS be able to keep it running for 3 hours?
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A 3000 VA UPS will probably not be able to run your equipment for three hours.  It depends in part on the model and its efficiency, however.  

Take a look at the Runtime graph on this page, for a APC 3000VA UPS unit:

If your combined wattage were 500 watts, the  UPS would only power the equipment for one hour.
Zephyr ICTCloud ArchitectCommented:
If you use the APC UPS selector and put in 500 or even more Watts, it tells you that even a 1000VA would be enough for +4 hours
Tony GiangrecoCommented:
The APC UPS's come with PowerChute software that shuts your PC down before the battery runs dead.

If you just need your PC to run but shutdown before this happens, just install that software and connect your PC to it's USB connection or set it up with the network version of Powerchute.

If you do have a power failure, don't forget about your router and network switch. if they lose power but your pc stays up, you still lose internet access killing email and browsing.

We use multiple APC 2500 & 3000 UPS's in our server room. APC is a great brand.
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It would be informative to know the actual power draw of your computer to make this calculation.  I've used a device called Kill-A-Watt (under $18 from Home Depot) to make such a measurement.  You plug it into the wall outlet and then plug in whatever you want to measure.  It will display a number of things, including Watts or VA.  You can even have it accumulate the usage over time and display kWh.  This can be a much more accurate way of determining your energy needs.  Once you have an accurate measure of your power draw, you can use the UPS selector to give you an accurate estimate of run time.

Keep in mind that the VA rating of the UPS is the limit of what you can draw from the battery at any moment and not the capacity (total energy/run time) of the battery.  While higher VA UPSs typically have more battery capacity, that is not necessarily the case.
Gary CaseRetiredCommented:
"... Will a 3000 VA UPS be able to keep it running for 3 hours? " ==>  Most likely NO.

To answer more definitively, you need more information.   Your PC has a 400w power supply, but an i3-based system with an SSD likely doesn't draw more than 60-80 watts during normal operation -- possibly even less.   So the first thing you should do is buy a Kill-a-Watt [mentioned above & available here: ]  and measure the actual power consumption of your PC.

Once you know that, you can go to APC's  "UPS Selector" site [ ]; put in your load and runtime, and it will provide you with some suggestions.    What you'll most likely need is a good UPS unit AND one or two auxiliary batteries to provide that much runtime.

For example, if you need 100 watts, the least expensive option shown at APC's site is a Back-UPS Pro 1500 plus one BR24BPG auxiliary battery pack.    That combination will provide 219 minutes of runtime at 100w for a cost of $409.98  [Available for less at many online sources].

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Don't forget to include the LCD screen,  and connected devices as well when measuring the power needed !
>>  you have to power the screen also
Tony GiangrecoCommented:
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