Newsgroups: sci.electronics
Path: utzoo!henry
From: henry@utzoo.uucp (Henry Spencer)
Subject: Re: battery chargers
Message-ID: <1989Dec3.001928.7622@utzoo.uucp>
Organization: U of Toronto Zoology
References: <28220@amdcad.AMD.COM>
Date: Sun, 3 Dec 89 00:19:28 GMT

In article <28220@amdcad.AMD.COM> phil@diablo.amd.com () writes:
>And out of curiousity, how do the corresponding NiCad systems work?
>I'm used to overnight, 1/10 rate chargers but lately I've seen a
>Norelco cordless shaver that magically recharges in about an hour, as
>well as a Makita 9.6V systems that recharges in about the same time. I
>am told the Makita just dumps energy into the battery and stops when
>it gets hot; it certainly does get hot...

You can recharge nicads at blinding speed if you are equipped to monitor
the temperature or internal pressure of the cells.  The problem is that
it's difficult to tell whether nicads are fully charged by looking at
their electrical behavior, and high-rate overcharging causes overheating
and internal pressure buildup.  Military nicad systems often have sensors
for pressure or temperature to permit rapid recharge.  It should be
possible for shavers and the like if the nicads are custom-made for them.

Exactly how the shavers do it, I'm not sure.  I took my Philips shaver
(Philips products are marketed under "Norelco" in the US for some reason)
apart a while ago out of curiosity.  In contrast to my old one, which
was about as simple as they come, this beast is pretty smart.  It knows
when it's low on charge, it knows when it's fully recharged, and you can
plug it into either 110V or 220V without flipping any switches.  Turns
out the thing has a zillion-legged IC inside it, along with assorted
other cryptic components.  Judging by the tiny little multi-winding
transformer, the lack of any obvious 110/220 switching even internally, 
and the FCC-compliance sticker (!) on the case, I suspect it's a switching
power supply (!!) managed by that mysterious IC.  I didn't think to
look at the battery to see if it had any extra connections for something
like temperature sensing.
-- 
Mars can wait:  we've barely   |     Henry Spencer at U of Toronto Zoology
started exploring the Moon.    | uunet!attcan!utzoo!henry henry@zoo.toronto.edu


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