[vox-tech] UPS and auto battery

[Rod Roark]

Thanks Ted, that's really good info.  It sounds like my old
cheapie APC is not a good foundation for a better UPS.

Actually I'm more interested in handling extended outages
than in instant failover.  I use Reiserfs for just about
everything here and it has been reliable so far in not
trashing things when power fails.  Maybe I'll just go for
the inverter, a deep cycle battery and a moderately cheap
charger, and keep them on hand but not actually running the
computer all the time.

BTW do you know anything about gasoline-powered generators?
That may be a more comprehensive solution.

Thanks again,

-- Rod

On Saturday 06 March 2004 10:53 pm, Ted Deppner wrote:
> 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/