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Subject: Re: Difference between AC adapter and charger?
References: <0001HW.B9D43FDF0325BBB11662EAD0@news.covad.net> <0001HW.B9D4EE870344BA681662EAD0@news.covad.net> <3DB01FBB.EAF744F9@usa.net> <0001HW.B9D572FB034E39101662EAD0@news.covad.net> <3DB02E27.email@example.com> <3DB42BB1.EC27E431@bellatlantic.net> <3DB4C57E.B06B96D5@bellatlantic.net> <3DB61379.5EFB8B5C@bellatlantic.net>
Date: Wed, 23 Oct 2002 17:01:53 GMT
NNTP-Posting-Date: Wed, 23 Oct 2002 13:01:53 EDT
Phil Allison wrote:
> wrote in message
> > Phil Allison wrote:
> > > ** Then that includes 95% of all wall warts.
> > I haven't mentioned wall warts.
> ** That is the topic here - read the heading.
Gee, Phil, I see the word "charger" up there, right in the
heading where you want me to look. You need to read the
WHOLE heading. Nor did you restrict your responses to
either AC adapter, wall wart or charger.
> > > That has nothing to do with the issue of
> > > > whether you are charging the cells with voltage regulation
> > > > versus current regulation, however.
> > >
> > > ** It has *everything" to do with it. The term "constant
> > > implies NO current limit.
> > I've repeatedly mentioned current limiting, yet you choose
> > to respond to a nonexistent implication. I was specific
> > and strong in describing a constant voltage supply that
> > would push enough current through a NiCd cell to make it
> > explode as an insane design.
> ** Then you are using the wrong term over and over.
No. When discussing a supply, I have used that term.
When discussing a charger, I have used that term.
> If the supply has
> a current limit circuit and is connected to a pack of Ni-Cds then it is
> ipso facto a constant current charger since the pack will draw current at
> that limit. The voltage on the pack will vary with the state of charge - how
> in God's name can that be called "constant voltage".
Wrong. The pack will not "draw current at that limit". As specified
in the example I posted, the current limit established by connecting
the 7.2 V battery pack to the supply through a 150 ohm resistor,
using a supply regulated at 13.8 volts, is 92 ma. But when the
pack is fully charged, it will draw 36 ma. - well below the 92
ma limit. Both the current through the cells and the voltage
across them will vary as they charge.
> So you are arguing with something
> > I not only never said, but specifically and strongly denounced.
> ** Rubbish - you posts were full of ambiguity and still are.
I'm beginning to see the light. You wish to argue for the sake
of argument. I don't. I apologize if my posts are not clear
> > >
> > > >
> > > > You may have missed the part of the post that mentions current
> > > > limiting. The fact that a supply is voltage regulated does not
> > > > preclude a current limiting resistance between the supply and
> > > > the load. Ohms law. :-)
> > >
> > > ** What? 0.27 ohms worth - gimme a break.
> > What are you talking about? Where did you come up with .27
> > ohms resistance?
> ** Read the whole thread mate - w toms gave that figure.
What w_tom posted is his affair - I did not use that figure, and
your response was to me, not him. If you disagree with what I
said, then use what I said as the basis for your disagreement -
not what someone else said.
If you take exception to what w_tom posted, take it up with him.
Don't assume that because a figure was mentioned once in a thread
that another poster uses that figure.
> Try 150 ohms between a 7.2 volt pack consisting
> > of 6 1600 mah cells and a 13.8 volt regulated supply. Worst
> > case - 92 ma. With the cells fully charged, 36 ma. It makes
> > a real nice trickle charger.
> ** That is what is known in the trade as constant current charging.
So you understand that a constant voltage supply through a current
limiting resistor (assuming values are properly chosen) does not pose
no problem. We agree!
Now, the next step is to graduate to constant voltage chargers.
Build a voltage regulator that provides a constant 8 volts
output. Connect it to your 7.2 volt battery pack. Put the
current limiting on the input side of the supply, such that
the supply is protected. You'll charge the cells to
somewhat less than full capacity - but wou won't harm them,
until a cell within the pack develops a short. Then you may
over charge the remaining cells, which is what I indicated
in my first post. For that reason, a constant current charger
is a better choice. However, considering that a cell in the
pack has shorted, it is time to replace the pack, anyway.
Where you lose out, possibly, is in repairing the pack by
replacing one cell. But the likelyhood of matching the new cell
to the other 5 is low, so repairing packs may not always be
the best choice. Usually, the best choice is replacing the
pack for most people.
FYI, "constant voltage" (as I believe tom_w had in mind) chargers
for NiCds exist in plenty. You mentioned wall wart style chargers -
most of them are of that type. They don't include much more than a
transformer & diode. They work fine. I would prefer a different
meaning to "constant voltage" than what I believe tom_w had in mind,
and I would also prefer a different meaning for "constant current"
that what you call it
"That is what is known in the trade as constant current charging."
referring to a constant voltage through a current limiting
To me, constant current means an unvarying current, or a
current that varies only slightly, as the cell charges.
Typically, constant current refers to the charge rate
as expressed by C/X, and it does not vary 56 ma.
> BTW Why did you snip my detailed explanation ??
I did not respond to it - so there was no need to include
it and waste bandwidth.
We have, as I see it, no technical disagreement. You
have explained what you meant by "dangerous" and using
your description of that term I no longer have a hard
time seeing how a simple voltage regulated charger is
> . . . . . . . . . . ..................... Phil
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