On Wed, 23 Aug 2017 15:31:09 -0400
rickman  wrote:

> Dave Liquorice wrote on 8/22/2017 3:34 PM:
> > On Mon, 21 Aug 2017 23:52:41 -0400, rickman wrote:
> >
> >>>> The fire alarms and emergency lighting are all SLA powered. The
> >>>> batteries are still good after about 10 years ...
> >>>
> >>> Not APC kit then, thier stuff cooks batteries in around 3 to 4 years.
> >>
> >> That's just not true.  I have APC units that have lasted over a decade
> >> and still going strong.  It might actually be closer to two decades.
> >
> > With orginal batteries and actually able to run off battery for
> > roughly the time expected for the load?
>
> Can't say.  It is hard to get that info from APC and I can't find a model
> number on the unit other than the info on top.  Mostly I'm too lazy to dig
> it up at the moment.  I am using it to power the modem and router and seems
> to do that for hours, so that's as much test as I need.  My laptop will only
> run for an hour or so on batteries, so no point in worrying about longer
times.
>
>
> > My APC UPS has a manufactured date of 11 Mar 98 and it is fine but is
> > on it's fourth or fith (I think) set of batteries. I found out the
> > hard way, twice, that even though it says the batteries are OK, fully
> > charged and decent voltage, try and draw any power from 'em and they
> > die very quickly. Last time there was a strange smell, eventually
> > tacked down to the UPS with an almost too hot to touch case. The
> > batteries:
> >
> > https://www.flickr.com/photos/allsorts-60/16591022171
> >
> > After that I looked up the spec for the batteries and recomended
> > float voltage v temperature. The APC charge voltage was nearer to the
> > specified cyclic charge voltage at room temperature let alone the 40
> > C that the batteries ran at. I "got at" the charge circuit reduced
> > the voltage down to what it should be for float charging at 30 C and
> > fitted a small fan. That was back in 2014, these batteries are still
> > good. Left to APC they'd be cooked or very nearly so by now.
> >
> > I've also seen a couple of rack mount APC UPS's with cooked/swollen
> > batteries. One had to be junked as to remove the batteries would have
> > required the chassis cutting apart.
>
> So you have a bad UPS, not bad batteries.
>
Umm. I think that was exactly the point being made.

It's now over 30 years since I did any serious work with batteries so things
have no doubt improved, but what I learned then particulalry regarding SLAs
might suprise. I was mostly concerend with standby use, so only studied trickle
charge situations.

First off, charge voltage is inversely proportional to temperature, and one of
the companies I contacted was kind enough to send me a schematic of a simple
compensated voltage regulator, with a thermister which had to be *in* *Thermal*
*contact* with the battery under charge. Of course, nobody does that these
days, they just rely on the ambient temperature being the same - thats if they
bother with temperature compensation at all.

Secondly, not all batteries (even from the same manufacturer) have the same
reference charge voltage - so check the specs. As far as I remember, for a 12V
22AH battery I saw between 13.7V & 13.9V. I think that was at 25 deg. not sure.

The life expectancies I saw at that time for that battery size were in the
range of 5-6 years for 50% retained capacity. That was with no deep discharges.
I remember being surprised that the curves suggested the life was slighter
shorter if there were virtually no moderate discharges over that time.

--
W J G

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