On Tue, 15 Aug 2017 18:11:25 -0400
rickman  wrote:

> Martin Gregorie wrote on 8/15/2017 4:40 PM:
> > On Tue, 15 Aug 2017 21:00:54 +0100, Richard Ashbery wrote:
> >
> >> In article , Dennis Lee
> >> Bieber  wrote:
> >>> On Mon, 14 Aug 2017 21:14:18 -0400, rickman 
> >>> declaimed the following:
> >>
> >>
> >>>> UPS typically use SLA, sealed lead acid, batteries, I suppose because
> >>>> of the cost.  Notice it is very hard to get capacity info on most UPS
> >>>> units.  They
> >>
> >>>  Lead acid typically works with cheaper charging circuits, and work
> >>> well with a continuous float charge -- unlike NiCad/NiMH/Lithium
> >>> rechargeable with their multistage charging cycles and warnings to
> >>> remove them from the charger when they are "full". .
> >>
> >> Don't modern charging systems for Lithium switch off after full charge
> >> is reached - this is my understanding for devices like phones and
> >> tablets but I guess may not be the case for UPS.
> >>
> > But are they bright enough to go on watching a fully charged Li battery
> > and to top it up when its self-discharged by 5-10%?
> >
> > That is what you need for a UPS or an emergency power system.
>
> You mean like the batteries in every laptop, cell phone, tablet and every
> other portable device you've ever seen?
>
>
> > As others have said, that is easy for lead-acid or NiCd, because you can
> > use a low trickle charge rate and leave it on for years without harming
> > the battery.
> >
> > Something similar may work for NiMH. I've never seen anything to say
> > whether it does or not. All I know is that the one device I own that uses
> > NiMH and has a built-in charger does not have a trickle charge mode or
> > fully charged detection. OTOH a multi-chemistry charger I use for battery
> > testing and cycling works well for lead-acid and NiCd, but its capacity
> > measurement doesn't seem to work as well with NiMH.
>
> Before Li ion batteries became so popular in portables they used NiCd or
> NiMH and all got charged just fine.  Most laptops aren't untethered when
> used.  Nearly all are used while plugged in and the batteries are allowed to
> run down about 5% before being topped off.  Every laptop ever made is
> designed for the lowest cost practical because they sell so many.  So of
> course there are chips around that do exactly this.

Not where I work.

The field engineers laptops have *much* better battery life than the two that
are teathered in the office. The office portable phones that sit in their
cradles all day also do very poorly, only these days, when the battery fades
you
can no longer replace it, and have to junk the whole kit (you can never seen to
get a compatible model 2 years down the line). All the battery operated test
gear shows the same pattern of behaviour, tio the extent that these days, in
the workshop we make a point of not running it teathered.

The fire alarms and emergency lighting are all SLA powered. The batteries are
still good after about 10 years - every month they are tested, and the lighting
run for 30 minutes.

--
W J G

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