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UPS Batteries...The Good, The Bad and The Ugly

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Posted by Too_Many_Tools on October 19, 2005, 3:02 am
 


I just finished working on a number of UPSs.

One thing I noticed was that many of the Sealed Lead Acid (SLA)
batteries were swollen and hard to remove.

Why do SLA batteries swell?

I did notice that the UPS manufacturers apparently do not design for
this problem. Many of the UPSs had to be partially disassembled to
remove the batteries because of the tight quarters the battery
containers presented. Very poor design in my opinion.

Any suggestions for preventing a recurrence of this problem?

Thanks

TMT


Posted by Anthony Matonak on October 19, 2005, 3:57 am
 


Too_Many_Tools wrote:

It's part of their failure mode. Likely a combination of excess
gases at high pressure, high temperatures generated from shorted
plates and decomposing plates making themselves into funny shapes.


Sure, replace the batteries when they fail instead of waiting
a few years. :)

Anthony

Posted by Windsun on October 19, 2005, 5:04 pm
 

A few years ago we did a check on a bunch of UPS systems installed locally
for computer backup in some local city and company offices - about 30 total.

Of those, about 1/2 had batteries good enough to even fire up the UPS, and
about 1/2 of those that did were very marginal, such as only having enough
capacity for 10 minutes instead of the rated 30 minutes or so.

Going by that, I would bet that nearly half of the UPS systems in the
country don't work.

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Posted by tim on October 22, 2005, 2:04 am
 



Back a few years ago when I was doing this kind of thing for a
living the group I was working with had standardized on APC UPSs
for several reasons.  One was the on-board self testing that could
be scheduled on a periodic basis where the system would actually
switch to battery and measure how long it took to consume 10% of
it's charge, and report that to the computer monitoring all the
UPSs.  Made it handy to check the battery status, etc.

Posted by RoughRider on October 19, 2005, 4:09 am
 

This is an economic situation in consumer devices where the commodity is
purchased, used, then chucked, never maintained, or fixed.  UPS systems
along with much of todays electronics are cheap enough to make that they
become landfill at the moment something goes wrong.  It can be cheaper to
buy a new laser printer (c/w toner cartridge) than to buy a replacement
toner cartridge.  But I degress.

People want small, so no space is spared to allow for a bulging battery.
Mechanically, it is easier to fit the battery tight than to come up with a
different restraining method with space buffer (read:  shave every penny off
that you can).  Conversely, it is also about fitting the largest battery you
can into the available space.

The typical cheap gel cell UPS battery lasts about 5 years.  There is also
heat in that UPS which doesn't make things easier.  In commercial
applications, a battery is considered for replacement when it gets to 80% of
its original capacity (IEEE guideline).  In the small UPS, people will
continue to use it until the load dies within seconds of a power failure,
well beyond battery end-of-life.  With bad cells internally, the battery
created some additional heat during recharging.... which caused the battery
to accept more charge current.... more heat...more charge.... leading to
thermal runaway and the bulging plastic you see.

There are methods available to detect thermal runaway:  Smart CPU
programming, temperature monitoring, etc... but it probably doesn't change
the fact that the manufacturer wants you to buy a completely new unit when
the battery fails.  Or many consumers would do this anyway.  You want a
cheap UPS, the temperature sensor gets removed along with some other frills.

For those that can switch the battery themselves, a new battery for a small
UPS costs between $2 and $0 wholesale depending on size.

The way they build things these days, next time you walk into a Walmart
store, consider where much of the goods will end up in 5 or so years!



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