Which UPS?

The following question hit my inbox today from an old friend in Chicago.  To paraphrase: “I am searching for a UPS or line conditioner for a $20,000 HP Designjet 815mfp.  Two brownouts hit our building recently and the repair technician blamed the necessary $3000 repair on not having the unit connected to a good UPS.  I’m trying to figure out which statistics are the important ones, especially if I don’t care about battery backup.  For example, how important is sine wave and which stats refer to the sine wave of a UPS?  We’re looking to spend between $500 and $1000 on a good UPS.  Any thoughts?

Wow, great question.  And thanks for being so specific about the problem, the value, make and model of the printer, and your budget for a solution.  When specifying a power solution of any kind, it’s always a good idea to start by knowing as much about the load as possible.

Reading The Manual
I began by browsing HP’s Designjet 815mfp User’s Reference Guide, Quick Reference Guide and Assembly and Maintenance Poster.  Here I learned that one should “connect the ‘Y’ power cable to a power outlet.”  OK.  Via Google, I was able to locate the Electrical Specifications section of the Product Specifications.  Here we learn that the Designjet 815mfp requires 100 to 240 V AC, 2 amps maximum and 150 Watts maximum.  Now that’s the information we’re looking for.

With the load information in hand, I took a quick perusal of well-known UPS manufacturer APC’s UPS Selector.  I chose ‘Configure by Load,’ entered 150 Watts and chose the US standard 120 V.  Allowing for their default 30% room for expansion and 10 minutes of battery-backed runtime in a non-rack-mount, non-redundant setup, HP recommended three options.  The three vary in battery size but not in features, beginning with the APC Smart-UPS 750VA LCD 120V at $329.99, the APC Smart-UPS 1000VA LCD 120V at $469.00 and finally the APC Smart-UPS 1500VA LCD 120V at $579.00.  If you purchase your hardware from CDW as many corporations do, your price range would actually be $309.99 to $518.99, and that’s before you factor in any discount that your organization may successfully negotiate.  Incidentally, with your load, your actual battery-backed runtime is projected to be from 31 to 116 minutes, depending on your selection.  Speaking as one who had to walk down 19 flights of stairs following a power outage in downtown Chicago several years ago, it never hurts to have a few extra minutes of runtime on a UPS regardless of where you’re at.

Well, that was quick.  The prices are within budget, the proposed solution is from a well-known manufacturer and carried by a trusted distributor.  But how do we know that this is the right solution for this situation?  Maybe we could go even cheaper?  And what about those sine waves?

Notice the term Smart in our earlier product description: APC Smart-UPS.  Like most UPS vendors, APC manufactures both regular battery backups and smart uninteruptable power supplies.  With a regular battery backup, the connected devices run off of line power until that disappears, at which point it cuts over to the battery very quickly.  These units are cheaper, and offer less protection to power fluctuations including brownouts.  With a smart UPS, on the other hand, your devices typically receive continuous, conditioned power via the battery, while the line voltage keeps the battery charged in the background.  The UPSes mentioned earlier feature a “pure sine wave output,” and are suitable for servers and similarly sensitive equipment including your Designjet 815mfp.

And sine waves?
I’m no electrical engineer, nor did I consult one despite having a semi-retired engineer (my dad) on speed dial.  Generally speaking, you want your AC waveform to look like the first pattern on the following graphic, and not like the second.  I’m unaware of any metric for selecting a UPS based on this feature, aside from hooking it up to an oscilloscope.  Rather than worry about it, I’d simply select a smart UPS with a good reputation.  Perhaps you’ve read more about this than I have.

[Image created by ‘Omegatron’ using gnuplot, and downloaded from Wikimedia Commons.]

Final Plug
APC UPSWere I looking to protect a $20,000 device and avoid another $3,000 repair bill, without needlessly overspending and getting a heavier solution than required, I’d probably split the difference and buy the APC Smart-UPS 1000VA LCD 120V from CDW for $452.99.  We combine knowledge and instinct to make these types of selections every day in IT, and are generally well satisfied with the outcome.

[Update 06/29: My friend who submitted the original question took his interest in sine waves a step further and dug up this gem from 2005.  A blogger shows the fairly squarish wave put out by two APC Back-UPS models as seen on an oscilloscope, followed by the sine wave put out by a Smart-UPS model similar to what I’d recommended.  Thanks.]

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