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From: Keith R. Williams
Subject: Re: Difference between AC adapter and charger?
Date: Wed, 23 Oct 2002 20:51:59 -0400
References: <0001HW.B9D43FDF0325BBB11662EAD0@news.covad.net> <0001HW.B9D4EE870344BA681662EAD0@news.covad.net> <3DB01FBB.EAF744F9@usa.net> <0001HW.B9D572FB034E39101662EAD0@news.covad.net> <3DB02E27.email@example.com> <3DB2A987.FA0DD93E@usa.net>
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In article ,
> "Keith R. Williams" wrote in message
> > >
> > > 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.
> > No they certainly do not! Lead-acid batteries are charged with a
> > current limited voltage source. The "taper charge", as you call
> > it, is simply the reduced current as the battery voltage comes up
> > to the charging voltage. The "charge current" is the current
> > limiter in operation.
> > >
> > > You probably damage the NiCds as well in the form of acquiring a
> > > memory effect or other undesirable artifact, such as reduced run time.
> > Nonsense! "Memory" is nonexistent in modern NiCds (it's an old
> > wives's tale). NiCds are most certainly damagedd by constant
> > charging by cheap chargers. The "dust-busters" and most
> > emergency lighting are perfect examples of how *not* to treat
> > NiCds. Indeed NiCds are exactly the wrong technology for such
> > appliances. I doubt you'll find too many NiCds in emergency
> > lighting applications.
> > NiCds require quite the opposite charging techniques as do Lead-
> > Acids. NiCds want a voltage limited constant current source.
> > ----
> > Keith
> Everything you said makes perfect sense except the old wives tale part.
That part works too. The "memory effect" hasn't been seen for
twenty years. The "memory effect", or more properly "voltage
depression" issues were solved back in the early 80s.
> NiCds will develop a "memory" when there is more than one cell involved. The
> memory idea was just a laymans term for an un equal charge on the cells. In
> a series of say 6 cells, if one of those cells for any reason (perhaps due
> to a variance in internal resistance) has a lower charge than the other 5,
> then it will present a problem when charging them. The 5 ~equal cells will
> reach peak, level off, then begin to drop (triggering any self respecting
> charger to stop;-) and the 6th cell, the one that was lower than the rest,
> will never have made peak. It is this cell that "remembers" and will cause
> the whole battery pack to misbehave. The set will be at it's useless stage
> much sooner. This is why many NiCd manufactures will say that once in a
> while you should let the device drain the pack as much as possible. It will
> help to level off and equalize the charge in each cell. gives it amnesia i
> guess. :-) Then this will allow the pack to fully charge on it's next cycle.
*NEVER* drain a multi-cell NiCd pack to zero! To equalize cells
charge them fully, perhaps a bit of an over-charge. Cheap NiCd
chargers bake the living daylights out of the poor things.
Intermediate chargers look for the negative dV/dt, which isn't
fool proof. Good chargers monitor the cell temperature to shift
from charge to float (or better - off).
This has *nothing* to do with the so-called "memory" effect
though. This effect does *not* exist in modern cells to any
detectable extent. Most people blame the "memory effect" for
packs that were ruined by reverse charged cells.
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