Choosing the right UPS

Question

I'm trying to determine the size of the UPS I should buy. Ideally, I would like something to keep my system on for an hour in case of a power cut but I don't have the budget for that. Basically I want the best price to backup time ratio.

My monitor is a Samsung SyncMaster F2380. I tried to determine its power consumption. I can find here http://www.cnet.com/products/samsung-syncmaster-f2380/specs/ that it uses less than 40W, but when I try to calculate its consumption myself based on the information given behind the monitor, I get much more values. Here is what I see :

AC 100-240 1.0A

When I use the method described here https://superuser.com/a/128510/304534 I find 240W so I don't know who to believe.

Besides the monitor I have a PC with a core i3 4330 and a GTX 750 Ti. Based on these charts http://us.hardware.info/reviews/4993/27/intel-core-i3-4330--i5-4440-review-affordable-haswells-energy-consumption-igpu-cinebench-115-max I can see that it will require less than 100W.

So I'd like to know what is the actual wattage/consumption of my monitor, then what UPS would be appropriate. What can I expect from a 390 Watts / 650 VA UPS?

Thanks

Answer 1

You want to find a unit big enough to ...

• handle the load (i.e. not trip the internal circuit breaker) when the power goes off
• handle the higher peak loads of motors (fans, hard drives) starting up
• maintain power for at least 15 minutes during an outage
• maintain power for as long as possible after that, within the limits of your budget

I recommend starting with APC's online tool to determine what size UPS you need at http://www.apc.com/tools/ups_selector/

Other manufacturers have similar online tools but APC is the most widely sold UPS.

CAVEATS and NOTES

• A 1 hour runtime is an entirely reasonable expectation in the real world. However, current battery technology makes that very expensive. Typical runtimes for home or office are more like 15 minutes.
  • With this, you can wait 5-10mins to see if the power comes back on.
  • If it doesn't, you've got another 5mins in which to do a clean, controlled shutdown so all your data will be safely saved.
• As others have said, you cannot accurately determine power usage from the specs alone. Their purpose is to indicate the maximums the electrical components can safely tolerate.
• The APC site lets you size by specs or by device categories.
  • I tried "by specs" first. Needs too much info you don't have.
  • "By device" gets you reasonable recommendations.

Based on the info supplied, their APC Power Saving Back-UPS 750 (750VA) for $110 should work fine. I've been running an older model like this for several years without complaint. If you can afford it, by all means get a larger unit. There are other brands that are cheaper and probably just as good.

When the battery finally wears out after 5-7yrs or so, it's probably worth just buying a new unit. I've replaced UPS batteries and found a new unit usually gives you better monitoring, switching, and/or surge-suppression technology for just a little more than the cost of a replacement battery.

(edit 2015-01-08)
Battery on said UPS died a few weeks ago and I found that battery prices have dropped a lot so I replaced just the battery (contrary to my advice above). So far so good. With battery prices at about a quarter to a third that of a new unit, if you don't need better electronics, replace just the battery with one from a reliable reseller.