[vox-tech] UPS and auto battery

[Seth Nagao]

While we're on the subject of car batteries, I just figured I'd mention
that some new car batteries don't have the acid liquid like normal ones. 
I know there's a few manufacturers out there, but only Optima comes to
mind right now (IANAOE).  Apparently, they're completely sealed, have a
paste electrolyte that isn't supposed to leak (and onto your carpet) if
the case cracks , and supposedly last longer.  They also aren't cheap. 
Just figured I'd share my thoughts and plans for a Ghetto-UPS (once my gel
cells kick the bucket).
--Seth

Ted Deppner said:
> On Tue, Mar 02, 2004 at 03:13:07PM -0800, Rod Roark wrote:
>> Thanks to everyone for the informative replies.  Probably
>> what I'll do is look for a smallish battery in an auto parts
>> store to experiment with, and post here again when and if
>> anything comes of it.
>
> Lots of good stuff already said, but figure I'll briefly chime in with
> some of my experiences.
>
> Those sealed lead acid batteries in good UPSs have a life of 2 or 3
> years on the outside.  They're not really good like a good marine
> battery for deep cycling, but being a lead acid they can take some
> abuse (very similar to a car battery).
>
> The issues with using a wildly higher current battery are fairly
> obvious. A 7Ah batter versus a "650 cold cranking amp" battery than can
> easily sustain 20+Amps for a good long time (10s of minutes).  A 7Ah
> battery would only look like a dead short to the charger for minutes...
> a dead car battery could look like a dead short for an hour.
>
> Dangers... Only the cheap car cells still give off hydrogen (under
> normal conditions anyway), you can get sealed car batteries.  I've seen
> 4 or 5 year old APC units burn up their circuit boards when new
> batteries where put in.  The low end units with < 10Ah batteries
> typically have a charge controller that's on a PC board.  Your typical
> car charge controller is an ABS plastic thing (or older bakalite).  Big
> difference in current capacity, heat load, etc.
>
> If you can handle the possibility of fire and things exploding, have
> some fun.  The current is enough to burn you and cause fires, but you
> can be safe about experimenting, and it's always fun.  (You might be
> able to isolate the inverter from the charge controller and then
> integrate your own charge controller for instance.)  In my estimation a
> small UPS is good for one or maybe two battery change outs, ie a
> battery change every 1 to 2 years, and the unit over all having a
> useful life of 3 to 5 years.
>
> All that said, investing in a heavy duty DC power supply, a car
> battery, and a DC-AC inverter would probably be a safer and ultimately
> less expensive and more useful endevor.  DC-AC inverter would be less
> than $100, battery $50 on sale for a decent one.  Not sure on the DC
> power supply, it would need to be able to sustane 25 Amps continuously,
> as you'd be actually running off the inverter the whole time and not be
> "switched from AC to DC on power failure".
>
> A simple car battery charger won't do for this (I've tried)... most of
> them have 'auto shut off' modes where they pulse on and off, while your
> battery drains current but the voltage stays high enough to shut off
> the charge sequence.  You can run like this for several hours though in
> a pinch.
>
> A good link for this is http://www.dansdata.com/diyups.htm which showed
> up on Slash dot a few years ago I believe.
>
> --
> Ted Deppner
> http://www.deppner.us/
> _______________________________________________
> vox-tech mailing list
> vox-tech@lists.lugod.org
> http://lists.lugod.org/mailman/listinfo/vox-tech