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How Does a UPS handle "dirty power, surges, etc?

Posted on 2009-05-19
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Last Modified: 2013-12-11
About 3-4 weeks ago, I worked on  PC that would simply power off in an orderly fashion.  The UPS unit was constantly beeping which meant the battery was exhausted.  I noticed the native UPS service in event viewer was shutting down due to a perceived power outage.  It would constantly shut down the PC even if I bypassed the UPS unit and plugged directly into a simple power strip.  

I disabled the service as I noticed APC had installed its on UPS service.  I thought there might possibly be some type of conflict.  I replaced the UPS with another APC model and everything seemed to be fine for 3-4 weeks.

I received a call today saying the computer had started to shutdown 1-2 maybe 3 times per day.  This is exactly how it started before until it got to the point it was shutting down immediately after startup.

The girls who work there say they regularly trip the breakers and have even seen sparks fly from the breaker box.  One of their husbands who is somewhat electrically literate swears they have some kind of power issue there.  I did notice that the APC software reported 53 incidents of dirty power over a week period.  I don't know how serious "dirty" power is, if at all?

Does anyone have any idea what may be causing this.  I have not returned yet but I have a strong feeling the UPS battery has become exhausted from constantly being used and is shutting down the computer again.  I guess my big question is why is it constantly switching to battery power?  Would a UPS switch to battery if there is a continuous surge coming into it or if there is some other problem with the quality of the electricity?

Bear in mind I dont know a lot about electrical issues.  Im just trying to use logic here.  Any advice would really be appreciated.
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Question by:cwilliambrown
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ElloDarkstar earned 200 total points
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Wow. I would suggest that an electrician take a look at the circuit, and then the UPS in place be thrown away/recycled/whatever, and the PSU on the computer be replaced or examined...

Essentially the way a UPS "cleans" dirty power is that it stores the current in a battery, then feeds a different power wave out to devices. In the process of storing the power, it can change the cycle, strength, speed, etc of the power waves.

When something goes wrong with a battery, or if there's a short, or if it's just overworked... then the process the UPS uses to clean the power could be avoided or compromised and whatever devices are behind the UPS could be damaged.
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by:garycase
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Does the UPS unit have automatic voltage regulation (AVR) ??   If not, you should get one that does.    With AVR the unit can electronically compensate for power irregularities within a modest % (typically 15%) without switching to the battery/inverter.   [NEVER buy a UPS without AVR]

... but it's also a good idea to have the power at that location checked by a licensed electrician.
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by:cwilliambrown
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This is a fairly cheap UPS around $100.  I believe the model is APC Back-UPS 750.  Not sure if it has AVR but will know later today.  
Would these power irregularities cause the UPS to switch over to battery power, which would in turn (after a certain time frame) cause the monitoring software to shutdown the PC?
Also, I was thinking that a UPS with dead batteries would still pass power through to a PC but I think I have found that to be untrue? Correct?
 
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The inexpensive APC units do not have AVR ... an unfortunate design compromise to keep the cost down.    For ~$100 UPS units, I was using Belkin units, which had AVR even on their relatively low cost units -- but unfortunately they've exited the UPS business.   Tripp Lite and CyberPower make some reasonably priced units with AVR, so I'll try them the next time I buy a UPS -- or buy one of the higher-end APC units (which all have AVR).  

Note:  You can still find a few Belkin units available -- I have both of these models, and they're both excellent:  
http://www.buy.com/retail/product.asp?sku=10372346&listingid=37057880&dcaid=17902
http://www.buy.com/retail/product.asp?sku=10391960&listingid=1311102&dcaid=17902
(Office Depot may have some in stock at a local store)

Without AVR there is less line-conditioning; and the unit will switch on/off of battery power very frequently if the voltage supply isn't stable.   Not only annoying, but not good for either the UPS or the connected equipment.    It shouldn't cause a shutdown ... unless it's happening so often that the battery is low or if it is staying on battery power long enough that the automatic shutdown timer is triggered.

... a UPS unit with dead batteries should indeed still pass power through to the PC; but if it encounters a condition where it attempts a switch to battery power that will likely result in a power failure to the PC  (without AVR this could happen even without a true power failure).
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by:IanTh
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do they have the ups plugged in the same segment as a fridge or kettle theses are noisy divices
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by:cwilliambrown
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There is a fridge that would likely be on the same circuit!  Also a blender and a microwave might be.
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by:garycase
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Those are all "dirty"devices that could cause fluctuations on the line.   If possible, they should be on a different circuit.   But a UPS with AVR would help mitigate the transient effects they cause.

Note that you can also buy an AVR to condition the line without the UPS functionality:
http://www.newegg.com/Product/Product.aspx?Item=N82E16812106005&Tpk=LE1200
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by:ElloDarkstar
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Are they running a couple dozen vacuums and electric lawn mowers on there, too?

Not a helpful addition, but I thought some humor would help.
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by:cwilliambrown
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LOL...they are running all kinds of crap.  After stopping by and speaking to the girl who is there all day, it seems the owner was confused.  The PC is NOT powering down itself again but it is locking up and causing them to have to restart it, from time to time!  
So the good news, I did indeed solve their original power issue a few weeks ago.  All looks well with the UPS!  However, I'm still convinced they have an electrical issue of some sort and maybe the better UPS is taking care of it.  And now I have another issue to figure out.
Don't you love how some people will say something has been happening ever since you left and you can prove it was happening way before...LOL
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by:IanTh
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well lockups can be caused by power spikes so it still could be a power problem.
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by:cwilliambrown
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Since this problem did not actually reoccur, I'm going to close the question and award points for the informative information that was posted.  Thanks!
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