On 26 Mar 2017 at 10:53, Greg Nokes wrote:

> > On Mar 25, 2017, at 11:54 AM, (via tml list)
> > More stories from the Great Blackout.
> >
> >
> > So being required to have backup power or the ability to cold start
> > just means that gear is installed. Doesn't mean that it'll actually
> > *work* when the real thing comes along. Not even if it has been
> > tested.
> >
> > Usually it's a *real* mess trying to *realistically* test emergency
> > power. You can make sure the generator runs, but unless you actually
> > cut the main power completely, and without warning, you can't *know*
> > that everything will work.
> >
>
> I used to work in an environment where the power systems were rather
> important - we were "allowed" 5 min of planned downtime a year.
>
> We had batteries in each equipment rack with 1 hr run time each. A
> room based battery for the datacenter with 2 hours runtime. A hydrogen
> fuel cell which could run the facility for 2 months. A diesel
> generator with 2 weeks fuel. And connections to two separate power
> grids.
>
> We tested it monthly.
>
> First we would cut utility power, and wait for the generator to cut in
> - that took a few minutes and tested the batteries. Then we would shut
> down the generator and the fuel cell would take over.
>
> It was fun to watch the first few times - but then it became pretty
> routine. :)

One real world situation that your tests didn't cover and has killed
more than one backup setup is having the utility power go away and
come back several times in quick succession.

This tends to fuck things up because the flucuating load does
interesting things to the switching gear for the batteries, and the
generator startup sequence won't like it much either.

This, BTW is why some older surge suppressor power strips require a
*manual* reset after a power failure. It protects the computer from
damage from the rapid up/down/up sequence.

I've had problems with power "flickers. My "best system would shut
off at flickers that other system (including several digital clock)
kept running thru.

I've still to replace the big UPs that vanished when they remodeled
my apartment a few years back, but I was able to replace the battery
in an older, smaller one for only $25 and tthat's enough to keep it
going thru a "blip". Even if it probably wouldn't give me as much as
30 seconds of run time if the power stayed off. As I can afford it,
I'll be replacing the batteries in other old UPSes and evenhtually
getting another big one.

Oddly enough, the current cable modem has built-in battery backup.
Which isn't much help since the router and switches aren't hooked to
UPses yet.

--
Leonard Erickson (aka shadow)
shadow at shadowgard dot com