RE: Re: External APC Batteries?

[Guy Clark <guyclark@xxxxxxx>]

HI, Andy!

Thanx for the detailed reply!
My plan is not to use actual automotive batteries, but the
"deep-discharge" type of battery, like those used (I believe) for
marine use.  They are roughly the size of an automotive battery, but are
different inside.  These have a lower peak current output, but maintain
their voltage level longer than automotive batteries which are designed for
high current short duration use, starting engines.
I plan on using heavy wire as short a possible between the batteries and
the UPS, probably no more than 24" at most, and of gauge as large or
larger than that already in the UPS (my recollection is that the wires
currently in the unit are 10 or 12Ga.   Since the load placed upon the UPS
will be light (remember, it's only to power the controller and ignitor of
the on-demand propane water heater, so it shouldn't be more than an amp
max, but I'll double check to be sure).

Once a power failure event is passed, I might just turn off the UPS and
individually charge the batteries from an external battery charger to avoid
overloading the internal UPS charger.

Since the garage is unheated, the temperature during the rainy season
(Dec-March or so) is relatively low, 10-15C so the UPS should be pretty
happy ;-).

Of course, polarity is important!  ;-).

I guess that if I do it, I'll report back to the group how it went, and if
I don't report back.... lift a pint in my memory!

;-)

Guy> To: ukha_d@xxxxxxx> From: andywhitfield2002@xxxxxxx> Date:
Thu, 20 Dec 2007 21:04:24 +0000> Subject: [ukha_d] Re: External APC
Batteries?> > 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

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