Have just bought the latest type of rechargeable *Hybrid* batteries from
Maplin, made by Uniross, called Hybrio. (also Argos are now selling them
made by Sanyo).

They are supposed to have the advantage over Nickel Metal Hydride in that
they don't have the 'memory effect'. Also the advantage of the Alkaline, in
that they dont self discharge at quite a high rate when not being used.

The charger I have is an Energiser designed for Nickel Hydride batteries and
which indicates when a battery is fully charged, by the charging light going
off. But when putting in the Hybrid batteries the light does not go off.

Is there an harm done to these hybrid batteries if they are overcharged?

"john d hamilton" wrote in message
...
Have just bought the latest type of rechargeable *Hybrid* batteries from
Maplin, made by Uniross, called Hybrio. (also Argos are now selling them
made by Sanyo).

They are supposed to have the advantage over Nickel Metal Hydride in that
they don't have the 'memory effect'. Also the advantage of the Alkaline,
in
that they dont self discharge at quite a high rate when not being used.

The charger I have is an Energiser designed for Nickel Hydride batteries
and
which indicates when a battery is fully charged, by the charging light
going
off. But when putting in the Hybrid batteries the light does not go off.

Is there an harm done to these hybrid batteries if they are overcharged?


The biggest harm would be if they are getting hot,


Best to protect your investment and get the right charger...
if the charger you have does not turn off, I'm sure it will greatly shorten
the life of the batteries

Have just bought the latest type of rechargeable *Hybrid* batteries from
Maplin, made by Uniross, called Hybrio. (also Argos are now selling them
made by Sanyo).

They are supposed to have the advantage over Nickel Metal Hydride in that
they don't have the 'memory effect'. Also the advantage of the alkaline,
in
that they dont self discharge at quite a high rate when not being used.

The charger I have is an Energiser designed for Nickel Hydride batteries
and
which indicates when a battery is fully charged, by the charging light
going
off. But when putting in the Hybrid batteries the light does not go off.

Is there an harm done to these hybrid batteries if they are overcharged?


Who knows? HAVE YOU ASKED THE MANUFACTURER? No, of course not. That's too
much trouble, isn't it?

Good grief. Do you expect the people in this group to have detailed
technical information about about a new product?

By the way, I've not heard of NiMH cells suffering from memory effect.

["Followup-To:" header set to 24hoursupport.helpdesk.]
On 2008-10-08, john d hamilton wrote:

[...]

The charger I have is an Energiser designed for Nickel Hydride batteries and
which indicates when a battery is fully charged, by the charging light going
off. But when putting in the Hybrid batteries the light does not go off.

Is there an harm done to these hybrid batteries if they are overcharged?

Uniross's European website makes no mention of "Hybrio" batteries, but the
US website does - describing them as NiMH type. That site also offers
suggested 'charge times' using a variety of (presumably Uniross-branded)
chargers. For AA size 2500mAh, the longest time (presumably using the
simplest charger) is 30 hours.

Maplin's web site is as un-informative as usual.

http://www.batterylogic.co.uk/hybrio.htm say that these batteries "can
be recharged in /any/ NiMH battery charger".

I think that if your charger has an automatic cut-off calibrated for NiMH
cells, you should be safe enough - but don't leave batteries 'on charge'
indefinitely. There may be more information in the packaging of the
batteries you have, or in the packaging of chargers being sold for use with
such batteries.

--
-- ^^^^^^^^^^
-- Whiskers
-- ~~~~~~~~~~

On Oct 8, 4:14 am, "john d hamilton" wrote:
Have just bought the latest type of rechargeable *Hybrid* batteries from
Maplin, made by Uniross, called Hybrio. (also Argos are now selling them
made by Sanyo).

They are supposed to have the advantage over Nickel Metal Hydride in that
they don't have the 'memory effect'. Also the advantage of the Alkaline, in
that they dont self discharge at quite a high rate when not being used.

The charger I have is an Energiser designed for Nickel Hydride batteries and
which indicates when a battery is fully charged, by the charging light going
off. But when putting in the Hybrid batteries the light does not go off.

Is there an harm done to these hybrid batteries if they are overcharged?

If the light doesn't go off, they probably are charging. You could put
a meter in series with the batteries and check the charging rate after
a given charging period. You could check the charging rate at the
beginning and estimate the needed charging time so you could remove
them. With a VOM, you could also check the top voltage of the cells
before and after a period of time to verify the charge level. For
something simple, when they are overcharging, the battery will begin
to get warm or even hot. I can tell you from experience that a battery
can explode while charging. Lithium cells are more prone to it though.
I have not had a NMH type explode.

In article ,
john d hamilton wrote:

Have just bought the latest type of rechargeable *Hybrid* batteries from
Maplin, made by Uniross, called Hybrio. (also Argos are now selling them
made by Sanyo).

They are supposed to have the advantage over Nickel Metal Hydride in that
they don't have the 'memory effect'. Also the advantage of the Alkaline, in
that they dont self discharge at quite a high rate when not being used.

The charger I have is an Energiser designed for Nickel Hydride batteries and
which indicates when a battery is fully charged, by the charging light going
off. But when putting in the Hybrid batteries the light does not go off.

Is there an harm done to these hybrid batteries if they are overcharged?

According to the manufacturer web pages I've read, overcharging *any*
NiMH cell significantly can shorten its life... they're somewhat less
tolerant to this than nickel-cadmium cells. Also, it's somewhat more
difficult to detect the "full charge" state in a NiMH than it is in a
NiCd, especially at low charge rates.

Based on what I've read, there seem to be two charging schemes for
NiMH which the cells will tolerate fairly well:

- Slow charge (0.1 C or so) with a timed cutoff after 12 to 16 hours.
If you touch the cells during charging and find that they are
significantly warm, then they're probably "full". [They do warm up
somewhat during the normal charging process, so judging whether
they're warm enough to indicate full-charge is not always easy.]

- Fast charge (0.5C to 1C, or in some cases even higher) with primary
cutoff based on temperature rise, secondary cutoff based on zero
delta-V (i.e. the cell voltage stops rising when full-charge is
reached) and a timed cutoff as a failsafe.

Intermediate rates (above .1C and below .5C) have some
disadvantages... this amount of current may not result in a rapid
temperature rise at full-charge (thus making full-charge harder to
detect reliably) but is high enough to affect the cell's lifetime if
you do end up overcharging the cell.

It sounds to me as if your Energizer charger has its full-charge
detection circuit tuned properly for this newer type of NiMH cell. If
it's a slow (overnight) charger, you probably won't hurt the cells
significantly using it as long as you shut it down manually at the
proper time. If it's a "quick" or "fast" charger, it may very well be
overheating the cells enough to reduce their lifetime.

If you plan to use a lot of NiMH cells, or to recharge them
frequently, it might very well be a good investment to buy a
high-quality charger specifically designed for reliable fast-charging
of such cells. I like the Powerex MH-C9000 myself, as it's fast and
reliable and has a lot of useful features.

--
Dave Platt 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!

William Sommerwerck wrote:
Have just bought the latest type of rechargeable *Hybrid* batteries from
Maplin, made by Uniross, called Hybrio. (also Argos are now selling them
made by Sanyo).

They are supposed to have the advantage over Nickel Metal Hydride in that
they don't have the 'memory effect'. Also the advantage of the alkaline,
in
that they dont self discharge at quite a high rate when not being used.

The charger I have is an Energiser designed for Nickel Hydride batteries
and
which indicates when a battery is fully charged, by the charging light
going
off. But when putting in the Hybrid batteries the light does not go off.

Is there an harm done to these hybrid batteries if they are overcharged?


Who knows? HAVE YOU ASKED THE MANUFACTURER? No, of course not. That's too
much trouble, isn't it?

Good grief. Do you expect the people in this group to have detailed
technical information about about a new product?

By the way, I've not heard of NiMH cells suffering from memory effect.


NiMH cells have done very well for me, using a fast charger with a light
for each cell. After ten years, all twelve still hold a charge for weeks.

If more than one cell is charged on the same circuit (the same indicator
light), the charger should shut off when the first cell is charged.
With each charging cycle, the state of charge of the lowest cell may be
lower and you'll get less service out of the set of batteries. It could
seem like memory effect. The solution is the same, to drain each cell
and then charge.

"john d hamilton" wrote in message
...
Have just bought the latest type of rechargeable *Hybrid* batteries from
Maplin, made by Uniross, called Hybrio. (also Argos are now selling them
made by Sanyo).

They are supposed to have the advantage over Nickel Metal Hydride in that
they don't have the 'memory effect'. Also the advantage of the Alkaline,
in that they dont self discharge at quite a high rate when not being used.

The charger I have is an Energiser designed for Nickel Hydride batteries
and which indicates when a battery is fully charged, by the charging light
going off. But when putting in the Hybrid batteries the light does not go
off.

Is there an harm done to these hybrid batteries if they are overcharged?

Have you used them yet or are you putting them in the charger straight from
the box?

If they are new they will be fully charged already. My understanding is that
the 'sensor' for detecting full charge is the drop in current when the cell
goes from 'active charging' to ' fully charged'**, so it suggests that you
are probably currently 'over'charging them.

Let them run down and then try again. Calculate the approximate charging
time and start charging so that you can check if the charger light goes out
within an hour or so of the expected time.

**I'm not an expert on this, so I'm happy to be corrected on the mechanism
for detecting full charge.

On Wed, 8 Oct 2008 09:14:52 +0100, "john d hamilton"
wrote:

Have just bought the latest type of rechargeable *Hybrid* batteries from
Maplin, made by Uniross, called Hybrio. (also Argos are now selling them
made by Sanyo).

They are supposed to have the advantage over Nickel Metal Hydride in that
they don't have the 'memory effect'. Also the advantage of the Alkaline, in
that they dont self discharge at quite a high rate when not being used.

The charger I have is an Energiser designed for Nickel Hydride batteries and
which indicates when a battery is fully charged, by the charging light going
off. But when putting in the Hybrid batteries the light does not go off.

Is there an harm done to these hybrid batteries if they are overcharged?


Would it be to much trouble to identify the specific charger?

wrote in message
...
On Wed, 8 Oct 2008 09:14:52 +0100, "john d hamilton"
wrote:

Have just bought the latest type of rechargeable *Hybrid* batteries from
Maplin, made by Uniross, called Hybrio. (also Argos are now selling them
made by Sanyo).

They are supposed to have the advantage over Nickel Metal Hydride in that
they don't have the 'memory effect'. Also the advantage of the Alkaline,
in
that they dont self discharge at quite a high rate when not being used.

The charger I have is an Energiser designed for Nickel Hydride batteries
and
which indicates when a battery is fully charged, by the charging light
going
off. But when putting in the Hybrid batteries the light does not go off.

Is there an harm done to these hybrid batteries if they are overcharged?


Would it be to much trouble to identify the specific charger?

Many thanks to all. (except possibly Mr *Moody* Sommerwerck) The charger
is Energizer, Model; 'Compact Charger' (no serial numbers on it).

john d hamilton wrote:
wrote in message
...
On Wed, 8 Oct 2008 09:14:52 +0100, "john d hamilton"
wrote:

Have just bought the latest type of rechargeable *Hybrid* batteries from
Maplin, made by Uniross, called Hybrio. (also Argos are now selling them
made by Sanyo).

They are supposed to have the advantage over Nickel Metal Hydride in that
they don't have the 'memory effect'. Also the advantage of the Alkaline,
in
that they dont self discharge at quite a high rate when not being used.

The charger I have is an Energiser designed for Nickel Hydride batteries
and
which indicates when a battery is fully charged, by the charging light
going
off. But when putting in the Hybrid batteries the light does not go off.

Is there an harm done to these hybrid batteries if they are overcharged?

Would it be to much trouble to identify the specific charger?

Many thanks to all. (except possibly Mr *Moody* Sommerwerck) The charger
is Energizer, Model; 'Compact Charger' (no serial numbers on it).


Of 13 user reviews at amazon.com, 11 disliked it.

According to the manufacturer web pages I've read, overcharging *any*
NiMH cell significantly can shorten its life... they're somewhat less
tolerant to this than nickel-cadmium cells.

How do you define "overcharging"? Switching to a trickle charge at the end
of the charge cycle is, technically, overcharging, but no one considers it
abuse.

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!

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".

"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.

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.

The people in this group do not.


Also, it's somewhat more difficult to detect the "full charge" state
in a NiMH than it is in a NiCd, especially at low charge rates.

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.

William Sommerwerck wrote:
According to the manufacturer web pages I've read, overcharging *any*
NiMH cell significantly can shorten its life... they're somewhat less
tolerant to this than nickel-cadmium cells.

How do you define "overcharging"? Switching to a trickle charge at the end
of the charge cycle is, technically, overcharging, but no one considers it
abuse.

In 1975 my station got a hand-held communications radio with a NiCad
battery. The radio hung in a charger that would switch to a trickle
charge when the battery was charged. That would have been ideal for a
lead-acid battery, but in a matter of weeks the NiCad would no longer
take a charge. The boss contacted the battery manufacturer and learned
that NiCads should not be left on a trickle charge. Nobody considers it
abuse because it's not intentional misuse, but trickle charging is harmful.

I began using aa NiCads in 1981. They were supposed to be good for 500
charge cycles. Within about 50 cycles, their self-discharge was so high
that they would go flat if not used within a few days. Eventually they
wouldn't charge at all. I bought a lot of them for 17 years because I
found them more practical than alkalines even if I got only a fraction
of the advertised service life.

Then I tried a set of NiMH cells along with a microprocessor-controlled
500ma charger. They performed so well that I bought many more. After
ten years, all my NiMH cells will hold a charge for months. That
charger would also work for NiCads, and I discovered that they, too, had
outstanding service lives if fast-charged.

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.

On Wed, 8 Oct 2008 10:14, john d hamilton wrote:

Have just bought the latest type of rechargeable *Hybrid* batteries from
Maplin, made by Uniross, called Hybrio. (also Argos are now selling them
made by Sanyo).

They are supposed to have the advantage over Nickel Metal Hydride in that
they don't have the 'memory effect'.

Err, no. The claimed advantage is that their self-discharge rate is
extra low. Therefore they are sold in (allegedly) "charged" state, so
can be used straight out of the pack. After use and recharging, they
will allegedly still be holding a fair chunk of usable charge even
after many months of storage.

Also the advantage of the Alkaline, in that they dont self
discharge at quite a high rate when not being used.

Alkaline batteries are primaries, not rechargeable (at least, not with
great success / reliability / amount of recharge), and have
exceptionally low self-discharge rates, particularly when stored
unused.

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 a
Sanyo Eneloop
Panasonic Infinium
Vapex Instant

Hope this helps.

On Oct 9, 1:38 am, E Z Peaces 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.

On Thu, 9 Oct 2008 09:58:13 -0700 (PDT)
Al Bundy wrote:

A 12VDC battery applied to a 1.5VDC cell might be held
for about a second and no more.

Forward or reverse polarity?

Al Bundy wrote:
On Oct 9, 1:38 am, E Z Peaces 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.

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.

Tim Forcer wrote:

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 a
Sanyo Eneloop
Panasonic Infinium
Vapex Instant

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.

In article ,
William Sommerwerck wrote:

How do you define "overcharging"?

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.

Switching to a trickle charge at the end
of the charge cycle is, technically, overcharging, but no one considers it
abuse.

Actually, some of the manufacturer data sheets I've read seem to
recommend against it.

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!

True. That's one (not the only) definite advantage of NiMH cells -
they can be recharged very quickly.

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".

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.

"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.

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.

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.

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.


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.

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 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!

We have 240V which takes it from silly to mad.
"Al Bundy" wrote in message
...
On Oct 9, 1:38 am, E Z Peaces 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.

Dave Platt wrote:


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.
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.

I only use Ray O Vac alkaline batteries.
cuhulin

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.

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

Thank gawd I don't live on the left coast or new england either! Those
people are Crazy!
cuhulin

On Mon, 13 Oct 2008 12:02:06 -0700, UCLAN wrote:

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.

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.

PeterD 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.


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.

Nah, we just don't like to pollute our ground water.

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

[cut]

I am trying not to rely on Hybrio's supposed long-storage life, and to
carry a spare set of cells at all times.

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.

Tim Forcer wrote:

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.

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.

Wouldn't you know it? Just two days after I wrote
I got caught out.

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.

In article ,
William Sommerwerck wrote:
Wouldn't you know it? Just two days after I wrote
I got caught out.

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.

Indeed - which makes the self discharge rate pretty irrelevant. Especially
as even Ni-Cads aren't that bad.

--
*What was the best thing before sliced bread? *

Dave Plowman London SW
To e-mail, change noise into sound.