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If my power supply is 700w, do I need a 700w UPS?

I have a desktop that I built with a 750 Watt power supply. I'm looking to get a UPS for it and wondering if I need to find one that is rated at 750 Watts. Would a 720 Watt supply work?

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marked as duplicate by Xavierjazz, MaQleod, Ƭᴇcʜιᴇ007, Diogo, Olli Aug 16 '12 at 12:07

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If you give us your PC specs and a description of anything else you plan to keep powered on battery, we can give you an idea what size UPS you need. –  David Schwartz Aug 16 '12 at 0:42

2 Answers 2

The rated wattage of the power supply is not a factor in deciding the appropriate UPS size. The appropriate UPS size should be based on how much power the supply actually draws in that specific system, not the maximum it can supply.

A power supply's wattage rating is the maximum amount of power it can supply to the computer. What you want to know is the actual amount of power it's drawing from the computer.

You can often find watt meters at electronics stores for $20 or less. They're also available online. With these, you can measure how much electricity your equipment is actually drawing under various conditions, rather than having to guess or estimate it.

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UPS's have 2 main purposes in the home or small business

  1. Prevent a hard shutdown of the PC during a power outage, preventing data loss.

  2. Have enough battery run time to allow a graceful shutdown of the PC.

  3. Depending on the quality and model of UPS, they can also prevent low voltage or surge protection. More expensive small business UPS's can also perform Power Conditioning, actually improve the quality of the AC voltage supplied to the PC.

Choosing the correct size is somewhat difficult, because it is moderately difficult to determine just how much wattage your PC actually uses, this may also include a monitor if it is connected to the UPS. A 650 watt quality UPS should do the intended job (see #1 #2)

A quality UPS will include software and a data cable, with the software installed in the Operating System and the data cable connected from the UPS to the pc, the software can be configured to perform a graceful shutdown after a specified period of time (usually set mine to a 3 minute time out), in case you are not present when the power fails.

Home small business UPS's were never intended to give you a long run time while on battery, those types of UPS's are mainly for corporate data center use.

Spend your money on higher quality UPS rather than buying more UPS wattage than you need

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