Here’s the deal. The VA rating is more than the wattage a battery backup can maintain. About 60% more. Ok, so that swings from 55% to 65%. So, an APC 750VA can support roughly 450 watts. An APC 1250VA can support 750 watts. And an APC 450 can support 270-280 watts.

What does that mean? Volts X Amps = Watts. So, if you look at your power brick for your laptop, and you notice that it is 18.5 volts and 3.5 amps… that’s 65 watts. Now, you look at your monitor, and figure out what wattage IT uses… and you look at the little DC adapters for your drives and examine their outputs and see what THEY use… then you add up the watts.

Still don’t get it, eh? Well, I can’t tell you if 280 watts is enough for your setup, because I don’t know if your 20″ monitor is an LCD panel, or an actual CRT monitor.. and the wattage difference between the two is phenomenal. I don’t know what the wattage draw of each of your external drives is, because I can’t see the output ratings on the little DC power adapters. I don’t know what make and model laptop you are using, so I don’t know what wattage your power brick is rated at. You might have an HP DV series, only drawing 64 watts. You might have a Toshiba A series like mine, drawing 120 watts. You might have some Alienware or Fujitsu monster, drawing 180 watts.

But I do know how to calculate wattage. And now, so do you. So with some thought, and a pen and paper, you can know how many watts you are drawing total. THEN, you can take this little formula…

battery backup VA number x 60% = wattage it supports

and figure out what battery backup you need for your system.

And… the higher the wattage the battery backup can support, the longer it will last before it needs to be recharged.

end of line bon-gart