UPS - Should I look at Watts or VA?

[randommayham]

I am looking at getting a UPS for my system.

My computer has a P67 - i7 2600K and 750w PSU.

I also have a 500w stereo amp to power my speakers.

I can get a Watt meter to measure it, but I see that most UPS have 2 specs - Watts and VA.

The meter will tell me how many Watts it is using, but not VA.

Is VA important, or is Watts enough?

[gman863]

Watts is the easiest method for choosing a UPS. The best practice is to get one that has a little more power (watts) than your power supply and monitor combined.

First, I would pass on connecting your amp to the UPS. Getting one with enough extra wattage to run a 500-watt amp will drive your price up by about $150 (either one huge UPS or a separate UPS for the amp). Just use a decent surge protector on it.

Second, a UPS gives you limited battery capacity; it does not turn your desktop PC into a notebook. The purpose behind one is to (a) cover brief power outages and (b) give you time to do an orderly shutdown of the PC in the event of an extended power outage. APC models have a USB connection and software that will sense an extended power outage and automatically shut down the PC if you are not around. This prevents corruption of the OS and files on your hard drives. Although run times will vary depending on your exact setup and CPU use at the time of the outage, you should not expect more than 15-20 minutes of backup power.

This being said, APC makes the best quality UPS units. A 900-1000 watt should set you back between $150 and $200.

Hope this helps.

[Goldenskull]

I all so found out with an Ups will not last all that long if its in a Dusty place its like any other computer item too much dust is a bad thing But having an Ups is a good idea.

[Colemanguy]

If you want to keep on playing/gaming/using your pc during power outages of more then 15-30 minutes you want to look at a generator, with auto start, tied into your home's power service.

[Rikky]

Originally Posted by randommayham

Is VA important, or is Watts enough?

Use watts as Gman said but VA plays a role.

VA is pretty complex AC calculation to calculate the apparent power in an electrical system that has a reactive load i.e power flow both toward "Your computer" and back toward the power source "power grid" Most branded PSU have PFC's which limit this 'flowback' meaning "actual power" VA is closer to the "real power" in Watts,this difference is known as the power factor.

Many people recommend a power factor of 0.6 or 0.7 on a desktop computer so if your computer is 100W you want a VA upwards of 160-170 VA but its only an estimate as it varies greatly between power supplies.

Basically whatever your AC device says it uses in watts,it uses a little bit more which is wasted due to the transformer in the power supply. If I had to put it in in further laymen's terms for consumers I would say the wattage is what the UPS is designed to run at while the VA rating is how robust and well made the UPS is,you could think of this as your safety margin in case the devices you connect have high VA rating even though they are under the wattage rating.

So how big of a safety margin do you need if you don't know the VA rating of the devices and are not an electrical engineer or just don't care to find out? Its a good question and for that I'll hand over to one of the many online UPS VA calculators

http://bugclub.org/beginners/miscellaneous/upscalc.html