Path: utzoo!attcan!uunet!snorkelwacker!bloom-beacon!erspert
From: erspert@athena.mit.edu (Ellen R. Spertus)
Newsgroups: sci.electronics
Subject: Re: Car Battery Rechargers
Summary: What happens when a CS grad believes the *EE*CS on the diploma
Message-ID: <1990Oct8.150643.9818@athena.mit.edu>
Date: 8 Oct 90 15:06:43 GMT
References: <1990Oct4.222556.20668@athena.mit.edu>
Sender: daemon@athena.mit.edu (Mr Background)
Organization: Massachusetts Institute of Technology
Lines: 48


Oops.  I messed up pretty thoroughly on that one.  I guess I should
admit what should be obvious to all of you, that I only know digitial
electronics.  Like most CS types, I took my analog pass-fail. :-)

For those who are interested, this is was the ad said, so you can see
it without my misparsing and misrememberances:

	Avoid jumper cables and tow trucks altogether with this
	12-Volt "D" Booster Car Battery Charger.  Simply plug it
	into your cigarette lighter and turn on the control switch.
	It recharges your dead car battery in 10 minutes and you
	don't even have to get out of the car, let alone open the
	hood!  A must for winter drivers and people who forget to
	turn lights off.  $59.95.

I got many intelligent and detailed replies.  Although several people
told me to expect flames and that they had almost flamed me, nobody
did (at least not in email --- I haven't read the groups).  Thanks.
In addition to electronics details (which I still have go through
carefully to understand), I was told the following:

	- Consumer Reports wrote up these things and said they're
	  no good.  While it may get the battery to restart, you will
	  then need to replace the car battery soon.

	- You should buy one of those car batteries with a reserve
	  power supply.  [Good advice, but I just bought a regular car 
	  battery.]

	- Join AAA if you're worried about needing recharges.  [I have,
	  but it's always quicker to find someone who'll let you do a
	  jumpstart from their car than to wait for AAA.  I have cables
	  and know how to use them.]

Since my concern was from leaving my lights on and not cold weather, I
am now considering building a device I saw in a popular electronics
magazine that buzzes if you leave your lights on.  (I don't have the
magazine with me but can give details to anyone who wants more
information.)  Of course, learning to triple-check that I turned off
my lights might be easier.

Thanks again, everyone, for help and no flames.  I'll stick to NAND,
etc., gates, and the occasional diode, resistor, or capacitor for a
while.  Actually, if anyone could recommend a good introductory analog
electronics book, I'd appreciate that.  

					Ellen Spertus