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Rob Morley · Guest

On Thu, 9 Oct 2008 09:58:13 -0700 (PDT)
Al Bundy <MSfortune@mcpmail.com> wrote:

[quote]A 12VDC battery applied to a 1.5VDC cell might be held
for about a second and no more.
[/quote]
Forward or reverse polarity?

E Z Peaces · Guest

Al Bundy wrote:
[quote]On Oct 9, 1:38 am, E Z Peaces <c...@invalid.invalid> wrote:
William Sommerwerck wrote:

A big killer of nickel cells is internal salts. They allow electrical
leakage so a cell won>t hold a charge long and eventually can>t be
charged at all. These deposits increase during trickle or C/10 charging
but apparently not with fast charging.

There are ways to burn off those salts. I suppose it might be done
with a well designed apparatus to gain a bit more life from a dead
cell, but not economically practical. For emergency purposes or as an
experiment, one can "tickle" the cell with a high voltage. I have even
used 120VAC from the wall socket. This is not for the feint of heart
and I would not advise even experimenting without proper eye and other
protection. A 12VDC battery applied to a 1.5VDC cell might be held
for about a second and no more.
[/quote]
In 1982, first time I saw self-discharge progress to a full short, I
zapped it with a capacitor charged to 170 V. It would take a charge
after that, but self-discharge was still high. I decided fixing shorted
NiCads wasn>t worth much.

UCLAN · Guest

Tim Forcer wrote:

[quote]My experience of Hybrios is that they aren>t _much_ better than
standard high-capacity NiMH. Also, a significant percentage have
proved to have lower-than-nominal capacity, which has been a right
nuisance at times, and led to me checking open-circuit cell voltages
and sorting the not-very-good cells apart from the rest of the
collection.

I am trying not to rely on Hybrio>s supposed long-storage life, and to
carry a spare set of cells at all times. Where I might expect to
depend on full (or full-ish) charge (full day>s GPS hiking, camera
flash to be used at a wedding), I now always replace with fresh.
Others may have different experiences, and be completely delighted
with their Hybrios. This is just my experience of five packs of 4*AA
and three of 4*AAA. I charge in a Uniroos fast charger, which handles
each cell individually (these chargers are, IMO, much preferable to
the majority which force charging in pairs or quads), and the LEDs
change from flashing to steady at different times, which is partly due
to differences in the four charging circuits, but can also indicate
significant differences between cells. Obviously, the charger was a
really good one, because they stopped making it. But at least one of
Maplin>s high-rate chargers operates cell-by-cell.

Other manufacturer/tradenames for the technology are:
Sanyo Eneloop
Panasonic Infinium
Vapex Instant
[/quote]
There are a dozen or more manufacturers of low self-discharge NiMH batteries.
I use Kodak brand LSD NiMH AA cells in my AA flashlight, remote controls,
cordless mouse - just about everything that used to take Alkaline AA cells.
They>ve been in these devices for 5 months now without the need to recharge.

The only place I use Alkaline AA cells now is in my smoke detector and weather
sensing equipment. I>m sold on this type of battery.

Dave Platt · Guest

In article <i_6dnRE8Pq-BznDVnZ2dnUVZ_rrinZ2d@comcast.com>,
William Sommerwerck <grizzledgeezer@comcast.net> wrote:

[quote]How do you define "overcharging"?
[/quote]
Pretty much the way you do later, and the way that the manufacturers
seem to. "Overcharging" is when one continues to force charging
current into the cell, once the cell>s electrochemistry has reached
the point of saturation and no further useful electrochemical
conversion can be performed.

[quote]Switching to a trickle charge at the end
of the charge cycle is, technically, overcharging, but no one considers it
abuse.
[/quote]
Actually, some of the manufacturer data sheets I>ve read seem to
recommend against it.

[quote]NiMH cells can tolerate huge charging currents. MAHA specifically states
that do not recommend charging at _less_ than 1/3 C, and permit charge rates
as high as 1.0 C!
[/quote]
True. That>s one (not the only) definite advantage of NiMH cells -
they can be recharged very quickly.

[quote]Whether this applies only to their cells, or pretty much everyones, I don>t
know. But NiMH cells don>t appear to be particularly "delicate".
[/quote]
They>re not particularly delicate in terms of their rate of charge
absorbtion _during_ proper charging. As you say, they can eat a lot
of current.

They are, however, more easily damaged than NiCd cells by the
overheating which occurs if you continue to pump energy into them
after their electrochemistry has saturated.

[quote]"Overcharging" probably means, as others have suggested, continuing the
charge past "negative delta V" and continuing to charge at a high rate to
the point where the cell badly overheats.
[/quote]
I read "overcharging" as any continued charging past the point of
"full". High-rate and low-rate overcharging does affect NiMH cells
differently, as the latter doesn>t heat up the cells very much.

[quote]But, as I said in my "moody" missive, this is something you should ask the
manufacturer, as only it knows how its only cells respond to various
charging protocols.
[/quote]
True. Unfortunately, without further information about how the
specific charger operates and behaves, even the cell>s manufacturer
probably won>t be able to give a useful answer.

[quote]Yes and no. NiMH chargers can use either a rise in temperature (which might
be hard to judge when the sensor is not part of the battery pack) or a drop
in voltage to signal "full charge". The latter is supposedly larger and more
distinct at higher charge rates.

I don>t believe either of these apply to nicad charging.
[/quote]
Actually, both of them do, although NiMH and NiCd cells differ
somewhat in both of these respects.

During the normal charging cycle (when they>re still accepting
charge), NiCd batteries do not heat up very much at all... the
electrochemical process in these batteries is said to be endothermic
during charge acceptance. The cell>s terminal voltage rises slowly
during this phase of charging. Once the plates are fully charged up,
the electrochemical reaction changes, and a secondary reaction
develops which releases the energy as heat... and so the NiCd cell
heats up significantly. As a result of the change and the heating,
the cell>s terminal voltage stops rising, and actually drops
significantly. This reversal of the voltage curve with time isn>t
hard to detect, and most NiCd fast-chargers seem to use a "negative
delta-V" detection circuit to determine that the cell has reached full
charge and to shut off the current (or drop it to a trickle).

NiMH cells behave a bit differently. They do warm up somewhat during
the main phase of charging - the electrochemical reaction is
exothermic. Like a NiCd, their terminal voltage rises slowly during
the charge cycle. Also like a NiCd, when they reach full charge they
start dissipating most of the incoming charge energy as heat, and (in
a fast-charge scenario) they can get quite warm quite quickly.
However, the effect of this on their terminal voltage is a bit
different... it stops rising, but it doesn>t begin to fall
significantly until you>ve gone pretty far past the full-charge point
and gotten them pretty hot... and the manufacturer data sheets I>ve
read say that this degree of overcharging will shorten their life
appreciably.

So, the manufacturer data sheets I>ve read recommend using the
temperature rise (absolute and/or delta-temperature-over-time)
directly, using a thermistor, as the primary means of detecting full
charge in a NiMH. Zero-delta-V-over-time makes a good secondary
shutoff mechanism, and a timed shutoff for safety is also recommended.

--
Dave Platt <dplatt@radagast.org> AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

Mark Dunn · Guest

We have 240V which takes it from silly to mad.
"Al Bundy" <MSfortune@mcpmail.com> wrote in message
news:34d6c36f-4b2c-4011-87e2-1cff9d31228e@b31g2000prb.googlegroups.com...
[quote]On Oct 9, 1:38 am, E Z Peaces <c...@invalid.invalid> wrote:
William Sommerwerck wrote:

A big killer of nickel cells is internal salts. They allow electrical
leakage so a cell won>t hold a charge long and eventually can>t be
charged at all. These deposits increase during trickle or C/10 charging
but apparently not with fast charging.

There are ways to burn off those salts. I suppose it might be done
with a well designed apparatus to gain a bit more life from a dead
cell, but not economically practical. For emergency purposes or as an
experiment, one can "tickle" the cell with a high voltage. I have even
used 120VAC from the wall socket. This is not for the feint of heart
and I would not advise even experimenting without proper eye and other
protection. A 12VDC battery applied to a 1.5VDC cell might be held
for about a second and no more.[/quote]

E Z Peaces · Guest

Dave Platt wrote:

[quote]
During the normal charging cycle (when they>re still accepting
charge), NiCd batteries do not heat up very much at all... the
electrochemical process in these batteries is said to be endothermic
during charge acceptance. The cell>s terminal voltage rises slowly
during this phase of charging. Once the plates are fully charged up,
the electrochemical reaction changes, and a secondary reaction
develops which releases the energy as heat... and so the NiCd cell
heats up significantly. As a result of the change and the heating,
the cell>s terminal voltage stops rising, and actually drops
significantly. This reversal of the voltage curve with time isn>t
hard to detect, and most NiCd fast-chargers seem to use a "negative
delta-V" detection circuit to determine that the cell has reached full
charge and to shut off the current (or drop it to a trickle).

NiMH cells behave a bit differently. They do warm up somewhat during
the main phase of charging - the electrochemical reaction is
exothermic. Like a NiCd, their terminal voltage rises slowly during
the charge cycle. Also like a NiCd, when they reach full charge they
start dissipating most of the incoming charge energy as heat, and (in
a fast-charge scenario) they can get quite warm quite quickly.
However, the effect of this on their terminal voltage is a bit
different... it stops rising, but it doesn>t begin to fall
significantly until you>ve gone pretty far past the full-charge point
and gotten them pretty hot... and the manufacturer data sheets I>ve
read say that this degree of overcharging will shorten their life
appreciably.

So, the manufacturer data sheets I>ve read recommend using the
temperature rise (absolute and/or delta-temperature-over-time)
directly, using a thermistor, as the primary means of detecting full
charge in a NiMH. Zero-delta-V-over-time makes a good secondary
shutoff mechanism, and a timed shutoff for safety is also recommended.

I have two chargers designed to charge AA NiMH in three hours or less.[/quote]
I wish they sensed temperature, but it seems they work strictly by
voltage changes.

The first one was designed for NiCds as well. I don>t recall any
trouble with NiCds, and what you>ve written may explain it. With NiMH,
each charger has occasionally stayed on longer than expected, and I
removed the cells because they felt hot. I haven>t seen any signs of
damage from these incidents.

Before I bought my first NiMH cells, I looked at data published by an
amateur photographer using several brands of cells and more than one
charger. Sometimes when he took pictures he would find that a set of
cells hadn>t taken a normal charge. I think that>s a drawback in
charging more than one cell in series in a circuit designed to shut off
when a cell is charged. Even when each cell is charged in its own
circuit, I think gas bubbles formed in a cell during charging may cause
a voltage fluctuation that may shut off a charger. I wonder if that
happens more often with new cells.

Guest

I only use Ray O Vac alkaline batteries.
cuhulin

UCLAN · Guest

cuhulin@webtv.net wrote:

[quote]I only use Ray O Vac alkaline batteries.
[/quote]
Some of us are more financially conservative and environmentally savvy.
How do you dispose of your alkaline batteries? It>s against the law to
just throw them into the trash here in California.

Guest

I have a lot of Eveready rechargable batteries and the proper Eveready
battery gizmo recharger here.I am too lazy to fool around with that
stuff all the time, unlless a long power outage occurs.I can use one of
my inverters and charge those batteries up from one of my van batteries
if I need to.
cuhulin

Guest

Thank gawd I don>t live on the left coast or new england either! Those
people are Crazy!
cuhulin

PeterD · Guest

On Mon, 13 Oct 2008 12:02:06 -0700, UCLAN <nomail@thanks.org> wrote:

[quote]cuhulin@webtv.net wrote:

I only use Ray O Vac alkaline batteries.

Some of us are more financially conservative and environmentally savvy.
How do you dispose of your alkaline batteries? It>s against the law to
just throw them into the trash here in California.
[/quote]
Which goes counter to what the trash is for, too...

Then again, it>s California, where *everything* has been shown to
cause cancer and must have a warning.

UCLAN · Guest

PeterD wrote:

[quote]I only use Ray O Vac alkaline batteries.

Some of us are more financially conservative and environmentally savvy.
How do you dispose of your alkaline batteries? It>s against the law to
just throw them into the trash here in California.

Which goes counter to what the trash is for, too...

Then again, it>s California, where *everything* has been shown to
cause cancer and must have a warning.
[/quote]
Nah, we just don>t like to pollute our ground water.

Tim Forcer · Guest

On Thu, 09 Oct 2008 13:52 I wrote:

[cut]

[quote]I am trying not to rely on Hybrio>s supposed long-storage life, and to
carry a spare set of cells at all times.
[/quote]
Wouldn>t you know it? Just two days after I wrote that I got caught
out.

On Saturday, I took my camera and flash to a family gathering.
Because I knew the Hybrios in the flash had been there for several
months, and had been used for many dozens of flashes, I took a spare
set too. Sure enough, after ten or twelve flashes, the flash
recycling time became significant. Out with the old, in with the new.
One flash, flash dead - no recharge action at all.

Unfortunately, I hadn>t packed my mini digital meter, and there>s only
so much swapping of cells one can manage in an effort to find 4
vaguely-usable cells from a set of eight that must include at least
two completely flat cells.

Testing once back home showed one cell of the eight was really poor,
presumably one from the reserve set. Four more were in the
well-discharged area (but not absolutely empty), and three were low.
A "best" set of 4 gave only another dozen manual flashes.

So now I need to add "check all cell voltages in the spare set before
taking it out for use". Plus I>m being more careful about identifying
cells which aren>t taking or keeping as much charge as their
set-mates. None of which will bring back the missed opportunities of
Saturday.

I>ll carry on using the Hybrios, if only because they do seem to hold
part-charge better than standard NiMH, but I won>t buy any more.

UCLAN · Guest

Tim Forcer wrote:

[quote]I>ll carry on using the Hybrios, if only because they do seem to hold
part-charge better than standard NiMH, but I won>t buy any more.
[/quote]
Try one of the dozen or so alternative brands. I>ve has GREAT success
with the Kodak LSD cells and the Sanyo Eneloop LSD cells.

William Sommerwerck · Guest

[quote]Wouldn>t you know it? Just two days after I wrote
I got caught out.
[/quote]
I>ve learned from experience to take a big pile o' freshly recharged
batteries when I go out to photograph. One advantage of this is that I can
leave the flash on all the time, not having to switch it on and off as I
take pictures.


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