Re: External APC Batteries?

["Andy Whitfield" <andywhitfield2002@xxxxxxxxxxx>]

I'm so tempted to reply with just a smiley!   ;-)

But seriously......
So often I tell people about the dangers of batteries and UPSs yet
there is always someone who doesn't take it seriously enough.
Like when I sell a box of replacement batteries to someone, I always
tell them to remove jewellery, watches, etc.
Even a small 12v 7Ah battery has a short circuit current of up to
500 amps.  So if someone did short out the battery with, lets say,
their metal watch strap, they could find the watch strap welded to
their wrist bone!  (me resists temptation to put in a smiley)

As for a UPS blowing up.....
I've had a few go bang.  Not due to the polarity being wrong but the
switching circuit failing.
Lets say it's a 3kva UPS with 8 off 12v 7Ah batteries wired in a
48Vdc pack.  So that's 48Vdc at 1000 amps short circuit which is
48kW albeit monetarily.
You get 1 or 2 banks of FETs trying to handle this kind of power and
only 1 of 2 things will happen.  If the UPS has a quick blow fuse
then hopefully this will protect the UPS (and engineer).  Or if the
UPS isn't quick blow then 'hello fireworks'.  The FETs just blow
themselves to pieces.

I know a guy who tests second hand UPSs for an IT company.  For a
couple of years he had been plugging them in no problem.  One day
one goes BANG.  He wouldn't go near then for a fortnight!   And not
the only case I've heard of.

Hey Rob, I've got some nice 6kva UPSs with the battery string
voltage of 360Vdc.
You couldn't hold on to the UPS for me, while I power it up, could
you?   ;-)

Andy

--- In ukha_d@xxxxxxx, "Rob Iles" <rob.iles@...> wrote:
>
> Andy,
>
> Are you by any chance a pyromaniac / sadist?
>
> It's the smileys after the guys shed blowing up and again after
the 3kva box
> blowing up like a box of fireworks in someones face! :O
>
> (I'm joking - hope you take it in the spirit it's meant :-) )
>
> Rob
>
>
> On 20/12/2007, Andy Whitfield <andywhitfield2002@...> wrote:
> >
> >   Hi Guy,
> >
> > There are a few problems with this idea.
> >
> > You must use very heavy duty cables and keep the cables very
short
> > otherwise you'll have significant voltage drop over the cables.
> > This can cause the cables to get very hot and even melt the
> > insulation. Plus the UPS will switch off early as it will think
the
> > battery voltage is lower than it actually is.
> >
> > It's possible the UPS onboard microcontroller will have a problem
> > with the long runtime and switch off early. Though generally they
> > keep running.
> >
> > The charge time can be very long.
> >
> > Make sure the UPS has a fan that comes on for charging and
> > discharging otherwise it may overheat with the longer
> > charge/discharge times.
> >
> > Car batteries are a little different from UPS AGM batteries. The
> > car batteries may gas a bit. I remember a case where a guy left a
> > car battery on an old car charger in his shed. Unfortunately his
> > charger overcharged the battery and when he opened the shed door
and
> > turned the light on, the spark from the light switch ignited the
gas
> > and blew his shed up! ;-)
> > Make sure the batteries are well ventilated.
> > Also periodically discharge and charge the car batteries on a
good
> > car battery charger.
> >
> > There are proper long runtime UPSs that are designed for extra
> > battery packs. I do have some in stock.
> >
> > BTW make SURE you connect the batteries the correct way around. I
> > heard the other day of someone who connected them the wrong way
> > around on a 3kva UPS and the was a massive bang and huge arcing
to
> > the case. It's rather like a box of fireworks blowing up in your
> > face! ;-)
> >
> > Regards
> > Andy the UPS Man
> >
> > --- In ukha_d@xxxxxxx <ukha_d%40yahoogroups.com>, Guy
Clark
> > <guyclark@> wrote:
> > >
> > > HI, Jim!
> > >
> > > My biggest concern is the charging circuit...will it be up
to
> > charging a pair of automotive-sized batteries instead of a pair
of
> > motorcycle-sized batteries. My guess is that if I don't let the
> > batteries discharge too far, there shouldn't be a problem. If the
> > charging circuit is designed properly, I would expect it should
> > charge any sized battery (of the same chemistry and voltage
(number
> > of cells) ) but take longer for a 100AH battery than a 10AH
battery
> > (for example).
> > >
> > > I may just have to bite the bullet and get a pair of marine
> > batteries and hook them up in place of the original (dead)
batteries
> > and see what happens!
> > >
> > > Thanx!!!
> > > Guy> To: ukha_d@xxxxxxx
<ukha_d%40yahoogroups.com>>
From:
> > jim@> Date: Thu, 20 Dec
> > 2007 18:02:32 +0000> Subject: RE: [ukha_d] External APC
Batteries?>
> > > Never done it (but considered it a few time), can't see
there
> > being a> problem in principle.> > A few
considerations.> > Make
sure
> > the cables, and particularly connectors, are up to the job as>
there
> > are a lot of amps flying around!> > You will need something
to
stop
> > the batteries discharging into each other -> Big diodes are
harder
> > to find and not cheap.> > The UPS charger is unlikely to be
rated
> > for more batteries (unless it's an> expandable unit), so an
external
> > off-line system with a big changeover relay> to connect the
extra
> > capacity might be an option.> > > Jim>