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From: jgk@osc.COM (Joe Keane)
Newsgroups: sci.electronics
Subject: Re: Need help with neato customizing
Keywords: charging
Message-ID: <1763@osc.COM>
Date: 23 Dec 89 13:36:27 GMT
References: <19307@watdragon.waterloo.edu>
Reply-To: jgk@osc.osc.com (Joe Keane)
Organization: Object Sciences Corp., Menlo Park, CA
Lines: 26

In article <19307@watdragon.waterloo.edu> aeclark@watyew.waterloo.edu (Robert
Fridrich) writes:
>I have just bought a protable top o'the line Sony tape/radio/cd
>player, and I was thinking about attempting the following:
>	-Installing rechargable batteries (permenently) into the unit
>	and have them self recharge when the unit is pluged in.  And
>	also install a charge meter to tell me when the batteries are
>	running out.
>	Problem: Is this a good idea?  Would it be better to have a
>	different jack for the recharging?  When recharging how would
>	I regulate the input volatge into the unit, or should I have a
>	recharge mode and a play mode separate from one another.

It's easy to use a standard three-terminal regulator to supply constant
charging current.  The main problem is voltage drop.  The input voltage has to
be higher than the battery charging voltage by the drop through the charging
regulator; this voltage has to be higher than the battery nominal voltage,
which is higher than the voltage you'll get out of it when it's running down,
which has to be higher than the final voltage by at least the drop through the
main regulator.  These drops could easily add up to five volts or more.

Another possibility is to build a switching current supply to recharge the
battery from a lower input voltage.  This is a complicated circuit but it's
not actually as hard as it sounds.  There are chips which do most of the work
for you; just tack on a coil and other random parts.  Besides, you'll learn a
lot about neat stuff.