I wouldn't use a car battery myself. As everyone else has pointed out,
they can't be discharged and recharged repeatedly. They are hazardous as
heck around kids, pets, and adults.

If you need an uninterruptible power supply for a computer, you are
better off buying one intended for that purpose -- they all offer
voltage regulation and surge protection, and usually come with
impressive looking guarantees that your car battery manufacturer won't
provide.

If you need really hefty uninterruptible power supply, buy one of those
very large units capable of a few kilowatts of juice and which cost
about $5,000.

Bob Cochran

Ed Browne wrote:
> A few minutes ago, I spoke to my friend, who happens to be a chemist turned
> software developer, and he said that we are generally overly paranoid about
> hydrogen.  He said that whereas the car batteries had vents, most new ones
> are closed systems that don't require that you add water and have a catalyst
> to recombine the hydrogen and oxygen.
>
> He went on to say that most of the battery backup electronics, including
> his, has low voltage detection so that power is turned off when battery
> voltage drops below 11.5V.  He countered most of the concerns so I'm left
> once again thinking it may be a good idea.  Perhaps the smart thing would be
> to watch his system for a while to see what happens.
>
> Please don't shoot the messenger, but any counters to his arguments?  Anyone
> else doing this already?
>
> Thanks,
> Ed
>
>
> -----Original Message-----
> Subject: Re: [EE:] battery backup
>
>
> Ok.  Not a good idea.
>
> A friend had recently done this and I wanted to research it before I
> followed suit.  Thanks for stopping a mistake (and ruined carpets).
>
> Ed
>
> -----Original Message-----
> From: pic microcontroller discussion list
> [mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of David Schmidt
> Sent: Wednesday, March 31, 2004 1:26 PM
> To: PICLIST@MITVMA.MIT.EDU
> Subject: Re: [EE:] battery backup
>
>
> - hydrogen gas generation
> - Corrosive sulfuric acid fumes released during discharging.  This will wet
> any dust that collects on the top of the batteries, and will eventually drip
> onto you floor and eat holes in your carpet.
> - having to check fluid levels
> - sulfation - I don't think the charging technique is suitable for a wet
> cell.
> - your home owner's insurance being void when you make a claim :-)
>
> Dave
>
>>Can anyone think of a reason not to attach a car battery in place of the
>>sealed battery in a battery backup system?  I've got a few of these
>
>
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--
Bob Cochran
Greenbelt, Maryland, USA
http://greenbeltcomputer.biz/

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