[PLUG] Batteries and UPSs

[Keith Lofstrom]

Concrete floors or not, the question was whether car batteries work
on UPSs.  I tried it, with a Topaz charger/discharger meant for car
batteries, using some brand new marine deep-cycle batteries. They were
continuously being trickle-charged in a room temperature room.  They
were sitting on a few sheets of corrogated cardboard (in case they
leaked) in the unused fireplace in my office (in case they vented
anything lighter than air, like H2). 

I had 4 batteries in parallel - I had earlier tried some experiments
with a UPS that used 48V, so I had the batteries.  The lower impedance
of 4 batteries made no difference to the UPS;  all good UPSes limit
current during charge and discharge, so it does not matter if the
battery looks like 12V with 0.1 ohms in series, or 12V with 0.00001
ohms.  Of course, it does matter if something shorts out in the UPS,
which is why I was no longer experimenting with the 48V UPS, it would
have died regardless of the battery feeding its failure, but the failure
was "more spectacular" with 4 marine batteries than 4 gel cells.

I was careless;  I forgot to monitor the fluid level and the batteries
dried up.  Refilling with distilled water and appropriate battery acids 
did not help - they apparently sulfated or something.  I had to
recycle the batteries about a year after I bought them.   

My "take home" lesson is that batteries need maintenance, and that
lead-acid open batteries need more maintenance than UPS batteries.
My UPSes are now running on standard sealed UPS batteries, which I
assume are designed to last a lot longer in this kind of application.
They kick in about once a month when the power glitches, as it does
in the fall out here in the 'burbs.  Horny squirrels romancing the
insulators on the transformers - BANG,  Rocky the Frying Squirrel - 
out goes a branch line, and the circuit breakers flip to alternates.
But I digress.

If I had to store a LOT of power for UPSes, for example a data center
with a lot of computers that needed to stay up until the emergency
generator started, then lead-acid batteries with a monthly maintenance
check would probably be just the thing;  I would rather pay the tape
monkey to check cheap batteries instead of buying more-expensive
batteries. But for home and small business use, a good UPS that uses
sealed long-life batteries might be more convenient and less expensive
for careless people like me.

Keith

--- 
Keith Lofstrom           keithl at ieee.org         Voice (503)-520-1993
KLIC --- Keith Lofstrom Integrated Circuits --- "Your Ideas in Silicon"
Design Contracting in Bipolar and CMOS - Analog, Digital, and Scan ICs