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From: email@example.com (Robert Richter)
Subject: Re: Difference between AC adapter and charger?
Date: 22 Oct 2002 19:11:50 -0700
References: <0001HW.B9D43FDF0325BBB11662EAD0@news.covad.net> <0001HW.B9D4EE870344BA681662EAD0@news.covad.net> <3DB01FBB.EAF744F9@usa.net> <0001HW.B9D572FB034E39101662EAD0@news.covad.net> <3DB02E27.firstname.lastname@example.org> <3DB2A987.FA0DD93E@usa.net> <3DB2D4FC.B566FCAE@usa.net>
NNTP-Posting-Date: 23 Oct 2002 02:11:50 GMT
w_tom wrote in message news:<3DB2D4FC.B566FCAE@usa.net>...
> Only those who want to argue claim that lead acid batteries
> are being overcharged. There is nothing in my post that even
> hints at applying excessive constant voltage to a 12 volt car
> battery or to a NiCd. That idea is being added by others who
> apparently want something to argue about.
> A 12 volt battery is constantly exposed to 13.6 volts or
> slightly higher. Where are all those 12 volt battery
> explosions? Same is true of NiCds that have always been
> charged by a constant voltage. Where are all those
> explosions. What is nuts are those who claim a NiCd cannot be
> charged by a constant voltage.
> JoeBloe wrote:
> > What? Are you nuts? Overcharging a lead acid battery will cause it
> > to explode. ALL car battery chargers that I have ever seen have a
> > taper charge effect built into them.
> > You probably damage the NiCds as well in the form of acquiring a
> > memory effect or other undesirable artifact, such as reduced run time.
Let's understand that NiCd and lead acid are DIFFERENT!!!
Constant voltage works on lead acid because once the cells are
charged, they simply won't draw much current in the over-charge, which
results in a trickle charge. Even when dead, they won't draw
inordinate amounts of current.
I took 15V (which is "way too high" for a car battery) to a charged
lead acid battery and the current was only 3A. Over-voltage on a lead
acid battery simply results in very little current that slowly breaks
the water apart and vents the gases (or re-combines them in the
maintenance free batteries). Even on a dead battery, it is common to
let the internal resistance of the battery be the ONLY source of
current limiting, and the alternator can usually handle this because
lead acid batteries simply won't charge very rapidly. I have seen
lead acid batteries that state "No current limiting needed at 13.8V".
On a NiCD battery, if you go over-voltage, the over-voltage will not
lazily break a water molecule apart every now and then; it will break
apart a lot of molecules NOW. If you use current limited constant
voltage, as soon as you go into overcharge, you will head toward the
As far as battery failures, I had a battery rupture on my car and it
destroyed the alternator with it (electrically, not because of acid).
Very few people make it through life without hearing of a catastrophic
failure of a least one friend's car battery.
Your argument about wall-warts and NiCD's providing back-up
power--look closer--the batteries are not connected directly across
the wal-wart terminals.
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