Re: Re: External APC Batteries?

["Rob Iles" <rob.iles@xxxxxxxxx>]

:-)

*removes watch* sure, I'll hold on to your UPS - shipping details sent off
list ;-)

Thanks!!

Seriously - your warnings are very pertinent - and I hope people do take
notice.

Have a safe and happy Xmas/$festival of your choice/holiday,

Rob


On 21/12/2007, Andy Whitfield <andywhitfield2002@xxxxxxx> wrote:
>
>
> 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 <ukha_d%40yahoogroups.com>, "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><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><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>
>
>
>


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