Question on UPS units?

warlock110 · Post by **warlock110** » Thu Mar 10, 2005 11:48 am

i can get an APC 350VA unit for 22 dollar, so that's relatively cheap, but 350VA isn't gonna last me long, well i don't know exactly how long it's gonna last, but 350VA sounds a little weak to me, So I wanna buy 2. Is that a good idea.

m0002a · Post by **m0002a** » Thu Mar 10, 2005 12:44 pm

Don't confuse VA capacity with watts. A 350 VA UPS is only appropriate for about 200 watts capacity. My 725 VA APPC UPS is rated for 450 watts according to specs on the box.

ilh · Post by **ilh** » Thu Mar 10, 2005 1:06 pm

If you have Active PFC, I would expect your VA and Watts rating to be comparable, right?

PaulShapiro · Post by **PaulShapiro** » Thu Mar 10, 2005 2:25 pm

No, even with active PFC VA and watts are not equal. They use VA because it lets them quote the highest possible number. VA is the peak voltage times the peak amplitude of the current. Watts measure the true power, which is the product of the voltage and current. Since the voltage and current are sine waves, the watts are always significantly less than the VA. APC's web site will give the numbers for each unit, but the figures quoted above sound right: 350VA can only handle 200 watts.

Slaugh · Post by **Slaugh** » Sat Mar 12, 2005 6:52 am

You can use APC's UPS selector to determine how much power you need... All you need to do is tell which peripherals will be used on the UPS and how much extra power you want for future expansion. This will give the power you need and a list of all referring UPS made by APC. 350VAC is not that much. I use a APC BackUPS ES 725. 350VAC was not enough for my needs. Better buy a bigger UPS instead of two.

ChucuSCAD · Post by **ChucuSCAD** » Sat Mar 12, 2005 10:54 am

In all reality a "consumer level" UPS is only going to give you a few mins of up time. They are really designed for those quick brown outs, power flux, and very short black outs. Almost all of the UPS systems come with power down software, so when power is cut it will start a shutdown program on your computer to prevent damage.

But yes 2 will last you longer.

chucuSCAD

Atragon · Post by **Atragon** » Sat Mar 12, 2005 4:39 pm

I would disagree on that one, if one can't put out the power required to keep the system up and running, 2 wouldn't help as you would have to daisy chain them and you wouldn't be able to get enough juice from them. Just get a bigger single unit.

Having said that, if you've got multiple systems you want to have on a UPS, then multiple smaller units may be more cost effective than one really big one.

altoclef · Post by **altoclef** » Sat Mar 12, 2005 8:34 pm

Atragon wrote:Having said that, if you've got multiple systems you want to have on a UPS, then multiple smaller units may be more cost effective than one really big one.

Good point. Also, every UPS I've ever used can only be connected to one computer (via USB) for the purpose of unattended shutdown/hibernate.

An easy way to look at the VA vs. Watt question: with a UPS, the VA figure refers to the total power capacity of the battery, and the Watt figure is the maximum system load it can support (the rate at which power can be delivered).