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From: willie@iuvax.cs.indiana.edu (william hunt)
Newsgroups: sci.electronics
Subject: Re: Car Battery Rechargers
Message-ID: <63220@iuvax.cs.indiana.edu>
Date: 8 Oct 90 14:33:43 GMT
References: <1990Oct4.222556.20668@athena.mit.edu>
Organization: Indiana University, Bloomington
Lines: 42

erspert@athena.mit.edu (Ellen R. Spertus) writes:

>I saw a car battery recharger for $60 in the Rand McNally map catalog.
>If your battery is dead, you plug this into your cigarette lighter, and
>it recharges the battery (enough to start) from a D battery.  It seems
>like a neat idea.  I have a few questions:

>1. Has anyone used one of these?  Any comments?

>2. Can I build one of these myself?  I've built computers, etc.,
>before, and I have access to lab equipment.  Anyone know where I could
>get plans?  

>Thanks.  Please direct follow-ups to the appropriate group or email
>me.

>					Ellen

Do not waste your money or time on anything that runs on batteries to
charge a car battery.  The energy storage of a car battery is many
times that of a D-cell.  Most recharging devices that plug into
cigarette lighter are a joke.  These devices can not transfer enough
power quickly enough to get a car started without waiting a long time.
Users are tricked into thinking these devices work well when actually the
car battery itself recovered charge simply by letting it sit for 15
minutes.  There are 2 exceptions to the cigarette lighter devices.
Low Amp battery chargers that are used over night, and solar panels
that are used on the dash during the day.  The key with these devices
is that they charge the car battery for many hours.

My suggestion is to get a good pair of jumper cables for emergency
situations.  Get a pair with 4 or 2 guage copper wire, copper jaws,
strong springs, two different color wires, and a least 15 to 20 feet
long (batteries are always on opposite sides of the cars. Murphy's
Law).  The concern that most people have that hydrogen from the
batterys can explode is not true.  I have talked to battery engineers
about that.  What causes a car battery to explode is when the jumper
cables are hooked up backwards.  Do not be fooled by the colors of the
wires in the car, always check the + and - marks on the battery or use
a volt meter.  I hope this info is useful.

Willie Hunt