When is a UPS battery actually bad? APC SUA750

Ben Scott dragonhawk at gmail.com
Tue Jun 17 12:09:08 EDT 2008


On Tue, Jun 17, 2008 at 11:46 AM, Coleman Kane <cokane at cokane.org> wrote:
> At that point, in my experience, some of them start to become IPS'es:
> Interrupting Power Supplies. Some of them exhibit a behavior whereby
> they determine battery utility by cutting the power occasionally ...

  Yah, APCs perform weekly automatic self-tests, and other brands do
similar things.  In theory, it's not supposed to drop the load during
a self-test, but I've had them do just that.  I was in the machine
room when a 2000 VA rack-mount APC did a self-test, and immediately
dropped the the load and starting that incessant beeping noise.  The
alarm was superfluous, as I could hear all the fans and disks in the
equipment whirring down to a stop, soon followed by shouts from the
users.

> I wasn't aware of the comment earlier about the UPS destroying your
> surge protectors attached to it (rendering them tap-only). That is
> interesting...

  Most TVSSes one encounters are shunt-mode devices -- they work by
dumping excess energy into the equipment grounding conductor ("third
prong", "safety ground").  If you chain such together, they can end up
both shunting at the same time, making the "shortest path to ground"
question complicated and defeating the design assumptions of the TVSS.
 So don't do that, then.  If you're after more outlets, you can plug
non-TVSS RPTs into a TVSS, and/or plug multiple TVSSes into a non-TVSS
RPT in parallel, or both, but don't put more than one TVSS in series.

TVSS = Transient Voltage Surge Suppressor
RPT = Relocatable Power Tap (turns one outlet into multiple outlets)

  This has actually come up on this list before.  Lots of good info in
the archived thread:

http://thread.gmane.org/gmane.org.user-groups.linux.gnhlug/1307/focus=1332

-- Ben


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