# A tech talent here to calculate power for an UPS?



## Caliante (May 13, 2012)

Hi all,

I have ordered a Synology with 6 disks. I need to buy a UPS to protect it. As I understand zero about electricity (I miss that part of my brain) it is all very confusing; I seem not to be allowed to simply add up the watts of the disks and the synology, but I need to look at volts and amperes, even more important Volt-Ampere (what on earth is this all?), cook 'm up, take into account scary thing like power efficiency, sine waves, and so on and on. Please don't l*a*ugh, I am serious about this, I didn't understand all of this in high school and I still don't now (but I can do your taxes).

Could anybody tell me, in noob terms, step by step, how I calculate the power the UPS needs to have?

I am in your debt for this,

Thank you in advance.


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## vermaden (May 13, 2012)

An UPS has a specification, for example 1000W for 10 minutes, that means if Your hardware uses 1000W, then it will run about 10 minutes on that UPS, but if Your hardware will use 100W, then 1000W/100W = 10 times less, then You will have 10 times more on the UPS, 10 * 10 minutes = 100 minutes of work under UPS.


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## Terry_Kennedy (May 14, 2012)

Caliante said:
			
		

> I have ordered a Synology with 6 disks. I need to buy a UPS to protect it. As I understand zero about electricity (I miss that part of my brain) it is all very confusing; I seem not to be allowed to simply add up the watts of the disks and the synology, but I need to look at volts and amperes, even more important Volt-Ampere (what on earth is this all?), cook 'm up, take into account scary thing like power efficiency, sine waves, and so on and on.


With a pure resistive load (like a light bulb or a space heater), Watts = VA. With more complex devices which draw varying amounts of current ad different points in the 60 (or 50) cycle AC waveform, power factor needs to be considered.

Since for non-resistive loads, VA will be higher than Watts, UPS manufacturers generally rate their products in VA to make them look bigger than they actually are.

A good place to start would be the AC adapter (or device nameplate if there's no external adapter). As long as the disks are powered by that power supply, you don't need to worry about adding up all the individual device power requirements - you can just use the AC adapter rating as the maximum draw of everything it powers.

The UPS vendor's web site will hopefully give you UPS specs in both VA and Watts. It may also give you an estimate runtime for a given load on a particular UPS model. For example, here is the info for the APC Back-UPSÂ® product line. [Note that if you use the direct link and never visited the APC site before, you'll see all models, including international ones. If you've ever visited the APC site before, it will only show you the ones appropriate for your country/region.]

At the low end of the UPS market, "extended runtime" options (additional battery packs) are uncommon. To get longer runtime, select a higher-output UPS which will give you a longer runtime when not fully loaded.

Consider what else you might need to run on the UPS. For example, if your PC is on a UPS already, putting the storage server on a UPS might be more useful if your network router / switch was also plugged into the UPS, since that way your PC will still be able to communicate with the storage server during a power failure, and gracefully close any files it may have open.

Also look at what sort of UPS features are available for unattended shutdown - if you're not home when there's an extended power failure, all a "vanilla" UPS will do is keep things going for a while longer. If the UPS batteries run down before the power comes back on, the attached devices will just see a power failure. Some UPS models have USB or serial ports or network connections which can be used to tell the attached device(s) that the power will fail soon and to shut down gracefully. You'll want to select a UPS that uses a method that's compatible with whatever you're plugging into it.


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## wblock@ (May 16, 2012)

A UPS is just two things: an inverter and batteries.  The inverter has to be big enough to run everything plugged into it.  That's the "VA" rating, which as Terry says is overrated.  Having more capacity than you need isn't a problem.  The same goes for batteries, although bigger batteries just mean longer runtime.

Vendors generally have a home line and a business line.  The home line has rough square wave output.  The business line has smooth sine wave output and voltage regulation so they can handle 20% under- and over-voltage from the wall without switching onto batteries.

I like the APC Smart-UPS units of 700W and up.  They cost more, unless you know the secret way to buy them.

Final note: if you're considering APC, go to http://apcupsd.com/ to see the list of units that have proprietary communications and should be avoided.


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