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I need to purchase a UPS for my server Rack. The UPs will be supplying power to three devices. 2 IBM x3550 at ~700 max watts. And one IBM ds3200 with two power supplies drawing ~500 watts each. My current UPS claims (via (w/1000) * 4560 hours = 3435.72 kWh) that I am drawing an average of ~ 800 watts. I'm looking at an APC SMT2200RM2U 2200 VA / 1980W and an APC SMT3000RM2U 3000 VA / 2700 W. Will the first UPS be sufficient or should I be looking at the second?

Thanks -Craig

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How long of a run time do you want before auto-shutdown starts? – Zypher Jul 12 '12 at 15:57
5-10 minutes is good. – Albion Jul 12 '12 at 16:21
I like to mention a few things. Some might be obvious, some where quite unexpected to a std admin but non-electrian: 1) For computers power (in watts) does NOT equal voltage * amperage. APC had a nice white paper about this, but I do not understand it well enough to explain it further. 2) Battery capacity reduces over time. If you want 5-10 minutes shutdown time in 2 years plan for 20 minutes now. 3) All sorts of shop want to sell you stuff. I hate talking to marketing droids, but it is probably worth it to ask APC what solution best serves you. – Hennes Jul 12 '12 at 16:31
@Hennes: Your point #3 is why I am asking here. Sometimes it's good to get the info from an agnostic source. Even APC IMHO is trying to sell me something, if you know what I mean. – Albion Jul 12 '12 at 16:49
@Hennes The simple explanation: two types of electrical loads, resistive and inductive. Resistive just resist electricity moving (incandescent bulbs are perfect examples, using that resistance to superheat the element so it glows). Inductive loads use some capacitance mechanism to store and release electrical flow (like a typical electric motor); this variation causes constant fluctuation in the electric flow, which means the peak draw will be higher than average. The amount and frequencies of these differences is what screws with the UPS and sizing. Computers are a little of each type. – Chris S Jul 12 '12 at 17:55

APC has a great tool on their site that lets you add devices and then configure things like run time and future expansion APC selector tool This is for North America 110V Acll might help but I have found that the front line folks are more interested in sales than a perfect fit. A local VAR might be more valuable.

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