Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!yale!mintaka!ogicse!zephyr.ens.tek.com!videovax!bill
From: bill@videovax.tv.tek.com (William K. McFadden)
Newsgroups: sci.electronics
Subject: Re: Car Battery Rechargers
Message-ID: <6075@videovax.tv.tek.com>
Date: 8 Oct 90 16:31:29 GMT
References: <1990Oct4.222556.20668@athena.mit.edu> <4179@rsiatl.UUCP> <90280.102233JXS118@psuvm.psu.edu>
Reply-To: bill@videovax.tv.tek.com (William K. McFadden)
Organization: Tektronix TV Measurement Systems, Beaverton OR
Lines: 33

In article <90280.102233JXS118@psuvm.psu.edu> JXS118@psuvm.psu.edu (Jeff Siegel) writes:
>In article <4179@rsiatl.UUCP>, jgd@rsiatl.UUCP (John G. DeArmond) says:
>
>(about car battery chargers:)
>
>>A much better solution to this problem is to get one of these new batteries
>>that are actually 2 batteries on one with a switch on top.  run one down
>>and flip the switch for the other...
>
>Anyone use these batteries in their cars? I've wonder how they keep both
>batteries charged without having both batteries supply current across the
>output terminals.

They use diodes.  You can buy a little device for charging two batteries from
one alternator that keeps them isolated during discharge.  The second battery
is presumably used to power a secondary system such as an R.V.  The advantage
of this isolation is you can still start your truck if you accidentally leave
the the lights on in your camper.  Also, with appropriate switching, you can
use the second battery to start your car if you accidentally leave the
headlights on.

The new 2-in-1 batteries incorporate two separate batteries, isolator, and
changeover switch into one convenient package.  The secondary battery is
generally a lot smaller than the main one.  Most allow you to connect both
batteries in parallel for that extra oomph on cold mornings (just remember to
switch it back, or you'll end up draining both batteries next time you leave
your lights on).  Consumer Reports recently examined these batteries and found
they worked very well but were quite expensive.
-- 
Bill McFadden    Tektronix, Inc.  P.O. Box 500  MS 58-639  Beaverton, OR  97077
bill@videovax.tv.tek.com,     {hplabs,uw-beaver,decvax}!tektronix!videovax!bill
Phone: (503) 627-6920       "The biggest difference between developing a missle
component and a toy is the 'cost constraint.'" -- John Anderson, Engineer, TI