Hello,

I am looking at getting a UPS for my home theater setup, but need to size it correctly. I have the wattage available for all the components, except for the SUB-12 sub-woofer. The manual (small as it is) shows nothing, but looking at the back of the box, where the power cord enters, it shows 120V and 3.15AMP. From that, I calculated an electrical wattage rating of 378W, say 380 watts.

 Is my calculation correct, or will the power requirement be less / more ??

 Advice, anyone ??

Regards, André

 I would imagine that is a steady state current draw. Figure that spec is derived using a test signal before clipping. Actual useage ( depending on limiters etc... and if you could clip the amp in it... ) could come in higher than that steady state. I am sure QSC uses 1/8th power to figure on the mean average current draw of their amps. 

If you crank up the gain you may be able to draw more than that. I would figure at about 5 amps continuous would be a good figure to go with. If you size the UPS larger than needed... there should be no harm. That way the amp should never be starved for power on transients. Transient ( momentary draw ) can be much larger than the above figure of 3.15 amps.

Like Mike said ~5 amps is what I would consider a safe bet. A nominal power draw here the 3.15 amps may be a little lean,I also doubt the sub will need more than 5 amps even on peaks.

but as a general rule not all your equiptment will not draw it's max power at the same time. That gives you some wiggle room. Also a UPS is rated for how long it will run a load after the power goes out.

For example if you are just looking to use it to clean up power and prevent brown outs, then you don't care that it won't run your equip for 38 minutes.

I put one in for a someone whose problem was any time the power blinked, the PJ would turn on (and stay on) so we loaded it past it's rating because we only needed 10 seconds for the generator to come on. Now don't get too crazy, but look at what your trying to do......

BTW not all ups's condition power (depends on what you buy)

 Thanks 2 everyone that replied. My old UPS (which was totally overrated for my home-office) was "kapput", so I used APC's TRADE-UP feature to acquire a BR1500LCD backup unit, which is rated at 865 watts. Rounding up each piece of equipments wattage rating and then adding them together, I got the following:

AV/RECEIVER amp(220W) + DVD player(10W) + Cable Box(40W) + TV(200W) + SUB-12(400W) = 870 watts.

 Given the fact that I want the UPS to predominantly "smooth over" power spikes and short lived brown-outs, as well as give me the opportunity for an "orderly shutdown" in the event of a prolonged power outage, I think the BR1500LCD should do the job ......... other wise I'll get a separate UPS for the SUB-12, which clearly is the biggest power grabber here.

As mentioned before, most of the time most pieces of equipment will run at nominal current draw, not the max .......

.... and yes, I got another lightweight UPS for the home office .......

Best regards, André