Will this overload my UPS?

April 25, 2009 3:15 PM

I have a 850va 425w UPS battery backup with only 2 outlets. There is a small server, speakers, home theater projecter, lcd monitor, and router connected to a power strip. The power strip and a desktop plug into the UPS. Is this setup safe? I am concerned about short 1-second interruptions caused by bad electrical connections rather than power outages.
posted by lpctstr; to technology (8 comments total)

It all depends on the power requirement of your setup. The desktop itself might require between 200 and 300 W of power, and I wouldn't be surprised if the projector needs 500W or more (those lightbulbs consume a lot of power).

Look at the back of your devices, near the power connections, and you'll probably find a label that specifies power requirements, either as W(atts) or as A(mps). On regular 110V connections, 1A is equivalent to 110W. Add them all together and you'll have the answer.

My guess is that you should get a larger UPS, or perhaps two separate ones.
posted by sd at 4:01 PM on April 25

Look at the labels of the connected equipment and add up the VA ratings. (Or wattages.) I'm surprised the thing hasn't already complained with an overload light...
posted by gjc at 4:44 PM on April 25

Where I went to school, "va" (volts times amps) was the same as "w" (watts) so I don't understand how your UPS can have a different va rating than w rating.
posted by Chocolate Pickle at 7:31 PM on April 25

Watts and VA are the same for non-reactive loads- 500W is 500VA if it's a lightbulb. Not so much if it's a motor or a computer. VA ratings take AC weirdness into account.
posted by gjc at 7:36 PM on April 25

That's too much for a UPS that size to handle. I assume that you have one for the primary function of shutting off the server properly to avoid data loss as well as mitigate the issue of electrical noise. With that many demanding pieces of equipment on it, I think you're endangering it's usefulness. Why not buy a smaller UPS for the server alone?
posted by cgomez at 9:04 PM on April 25

Buy a Kill-a-watt and see what the total current draw of the setup is. You'd probably like it to carry the load for at least 5 minutes when new so that it remains somewhat useful for the intended 1 minute outage or short power blips as the battery ages.

Offhandedly, I'd use the one, so long as I didn't expect serious runtime out of it. My issues with data corruption due to power loss have been so infrequent that I wouldn't mind if the PC didn't have time to shut down properly.

FWIW, the nameplate current draw is next to worthless. Almost nothing actually draws that much except for an instant when you turn it on.
posted by wierdo at 12:27 AM on April 26

The UPS's load ratings aren't just for the ability to carry a load during electrical failures. Even if the power is on, clean and wonderful, the power has to pass through the UPS circuitry to get to the equipment. So even if the idle power of the equipment is within tolerances, the spikes in load when equipment is under heavy load or being turned on will damage the UPS. Maybe not instantly, but relatively quickly.
posted by gjc at 6:48 AM on April 26

I've overloaded cheap APC UPSes before. They work pretty well, the main drawback is that you I only got 1-2 minutes of battery operation before the thing ran down. However, these UPSes also have a test mode that activates about once a week. And half the time it wouldn't come back from the test properly, it would start shrieking like something was wrong. Very obnoxious. I finally gave in and stopped overloading the poor thing.
posted by Nelson at 7:57 AM on April 26