Xref: utzoo sci.energy:515 sci.electronics:7465 sci.med:11678
Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!ames!think!eplunix!raoul
From: raoul@eplunix.UUCP (Otero)
Newsgroups: sci.energy,sci.electronics,sci.med
Subject: Re: Electric cars?  Start with wheelchairs.
Summary: Recharging 12 volts
Keywords: electirc cars wheelchairs batteries
Message-ID: <772@eplunix.UUCP>
Date: 18 Aug 89 18:38:42 GMT
References: <3659@internal.Apple.COM>
Organization: Eaton-Peabody Lab, Boston, MA
Lines: 33

Hmmm. Not that difficult, actually, I'm surprised it hasn't been done.
To recharge off a car system might be awkward unless you upgrade the
alternator, but a couple of hefty voltage regulators to limit current flow
to 10% of the Amp-hour rating of the battery should do quite nicely off a
car voltage, plus a few parallel diodes to make sure no reverse flow happens
if the voltage is higher than the car. And a fuse just in case something
blows.... Take a look at the National Semiconductor LM117 for something that
can dissipate 20 watts easily, and only costs a few dollars. There is even a
good design for a constant-voltage, constant current recharger included in
the manual. This is what you really want for lead acids. Let me know if I
should post it. 

Off of 120 Volt house current, I would suggest a separate AC/DC converter
and use the same voltage regulator. Power One makes good ones, but anyone
should be able to whip you up *something* if you don't care too much about
precision outputs.

I suspect the major problem would be water-proofing and idiot-proofing it.
(What if I stuck my tongue in the socket and lightning hits the cord? That
sort of thing....) I just put a recharge circuit into some medical
equipment, and the safety standards are astonishing. The only way someone
can get fried with these standards is if they douse it in gasoline, shove
their head in, and light a match inside.

If your friend would like, I can send circuit diagrams. It's about an
afternoon's work to do, and would probably cost $50-$100 with case. Call it
6" cubed. Would that be reasonable?

-- 
			Nico Garcia
			Engineer, CIRL 
			Mass. Eye and Ear Infirmary
			eplunix!cirl!raoul@eddie.mit.edu