UPS failure modes (was: fire at NAC)

Joel Jaeggli joelja at
Thu May 29 20:35:54 UTC 2003

On Thu, 29 May 2003, Bill Woodcock wrote:

>     > I had a little 2000VA rackmount Liebert UPS catch fire in 1997 and another
>     > new and improved Liebert model almost catch fire about a year later.
>     > What have others experienced as the failure mode(s) for their
>     > UPS(s)?
> We had a two-hour grid power outage here in Berkeley yesterday, during
> which time our APC Symmetra 16kva fried two of its four batteries, and
> went into bypass mode, which meant that the transition back from generator
> to grid caused everything to reboot.  :-/
> I've seen two previous APCs (both Matrixes) fry batteries...  The
> batteries balloon up, and get really hot, and are too big to extract from
> the chassis.  APC's solution to this is to have us take the entire UPS
> offline for several days to completely dissipate the heat, and then try to
> force the batteries out.  Since this seems to be an endemic problem, you'd
> think they'd just design a chassis with somewhat more clearance around the
> batteries so that failed ones could still be physically extracted.

gell cells suffer from an electron mobility problem relative to 
traditional lead acid batteries. If you pull to much current off a stack 
of them you can boil the electrolyte off in a very big hurry, but because 
they're sealed they'll distent before they explode instead of just venting.

I have run a matrix 5000xr with 4 battery enclosures down to zero 
under 65% load (220 minutes) without any untoward effects. in 100% load 
or overload conditions without forced air cooling (we lose ours in power 
outages) things could get uncomfortably warm.

>                                 -Bill

Joel Jaeggli	      Academic User Services   joelja at    
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