Re: External APC Batteries?

["Andy Whitfield" <andywhitfield2002@xxxxxxxxxxx>]

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, 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> 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>
>