I Beg to differ with you.
I have on occasions, and know friends who have damaged
Ni-Cad batteries. They were damaged by partial depletion
then recharging. They were in sealed waterproof torches
and over a period of time the batteries were damaged by
that method of charging. I now always run my batteries from
full to empty no mater what type.
taz.


Top-up charging is the best regime for NiCd's used in a torch. Full
discharge every time simply wears out the cells unnecessarily.

Of course cells vary enormously in quality and it is virtually
impossible to buy decent ones from retail outlets.

--
Keith Lewis

I agree Keith there are a lot of variables to batteries and the way
they are charged. The trouble with most set-ups IMHO is one cell
will fail in the battery and then the battery as a unit starts to perform
badly. Good cells are hard to get hold of and can easily be damaged
by incorrect use. In my experience if a cell is sold with the label good for
2000 charge cycles I've found that, that number can be reduced by half
if not even 3/4. So in real terms a battery that should be good for 2000
charges sometimes only last for 500 maybe 1000 charges.
Not a scientific answer just my own experience.
taz.

"Peter W. Meek" wrote in message
...
On Wed, 16 Jun 2004 10:34:33 -0400, Glenn Ashmore
wrote:

NiCads develop a memory over time and can't be fully recharged unless
they are fully discharged occasionally.

This is (almost) a myth. The Ni-Cad memory phenomenon
does exist, but I can almost promise that no-one
reading this has ever experienced it.

I am sorry but you are not entirly correct.

Proven many many times and easy to repeat.
Take two brand new and identical radio controlled racing cars.
FULLY charge and discharge the nicads of one of the cars ten times.
Randomly and gently cycle the nicads of the other car ten times.
Race the cars.

Fully charged/discharged car WILL win.
Not only will the car win a short sprint race... It will also win an
endurance race.

On Thu, 17 Jun 2004 16:40:59 GMT, "Doug"
wrote:

I have also seen it happen...running wet cell NiCad's for a back up source
of power for cesium beam frequency standards. These units we periodically
discharged and recharged as a preventative maintenance procedure, and they
did develop memory. The fix was to vary the preventative maintenance
discharge time/amount. H/P factory support helped us solve this problem.
Doug K7ABX

Well, I must admit, you ARE one of the very few who
has experienced true "memory" in Ni-Cads. Taz will
have to look elsewhere for his problems with his
sealed waterproof torches. Unless he has found some
way to discharge them partially AND IDENTICALLY each
time (on for the exact same amount of time at the
exact same temperature, EVERY single time) then it
is something else that is reducing the capacity of
his Ni-Cads. (They DO wear out under normal conditions,
just not as soon and with as sharp a cut-off as when
the memory effect is the cause.)

On Fri, 18 Jun 2004 10:01:19 +0000 (UTC), "James"
wrote:


"Peter W. Meek" wrote in message
.. .
On Wed, 16 Jun 2004 10:34:33 -0400, Glenn Ashmore
wrote:

NiCads develop a memory over time and can't be fully recharged unless
they are fully discharged occasionally.

This is (almost) a myth. The Ni-Cad memory phenomenon
does exist, but I can almost promise that no-one
reading this has ever experienced it.

I am sorry but you are not entirly correct.

Proven many many times and easy to repeat.
Take two brand new and identical radio controlled racing cars.
FULLY charge and discharge the nicads of one of the cars ten times.
Randomly and gently cycle the nicads of the other car ten times.
Race the cars.

Fully charged/discharged car WILL win.
Not only will the car win a short sprint race... It will also win an
endurance race.





What you are seeing has nothing to do with "memory effect".
A new nicad cell needs to be exercised several times to bring it up to
its full capacity. The capacity as to charge / discharge cycles is
sort of a bell shaped curve. Brand new not as much, after several
charge discharge cycles the capacity peaks, then it starts declining
with more charge discharge cycles.

When discharging them you should never discharge them below about 1
volt per cell. Doing so you run the risk of a cell being reverse
charged and that is the kiss of death for that cell.

Also nicad's don't like to be float charged like a lead acid battery.
A lead acid battery is as happy as can be when it is properly float
charged. A nicad is not. It will kill them. A nicad is not the proper
battery type for standby power.

Don't let a nicad get too hot when charging as that will cause the
cell to vent. Once a cell vents it is pretty much history.

By the way, there is no such thing as "memory effect". The very early
ni cad cells had sort of that problem but it does not exist in modern
cells.

Regards
Gary

In article ,
says...

Also nicad's don't like to be float charged like a lead acid battery.

What does "float-charged" mean?

On Fri, 18 Jun 2004 17:00:22 +0100, Stefan wrote:

In article ,
says...

Also nicad's don't like to be float charged like a lead acid battery.

What does "float-charged" mean?

"Floating a battery" refers to keeping a constant voltage charge on
the battery that is just high enough to replace the natural losses in
the battery. This is typically done with lead acid batteries that are
to be maintained at peak charge but not used for long periods.

A fully charged 12 volt lead acid battery has a voltage of around 12.7
volts. It will slowly discharge itself with no load on it if left
alone.
If a constant 13.3 to 13.6 volts (depending on temperature) charge is
left on the battery it will replace the self discharge energy of the
battery. This voltage can be left on the battery indefinitely and will
not harm the battery. Any higher charge voltage, only by a few tenths
of a volt, for long periods will harm the battery.

When initially charging the battery the voltage needs to be at around
14.2 volts for finishing the charge. Some gassing of the battery needs
to take place in the final phase of charging, slight overcharging, in
order to properly top off the cells. Then switch to the float voltage
13.3 volts to maintain.

Regards
Gary

"Doug" wrote in
nk.net:

I have also seen it happen...running wet cell NiCad's for a back up
source of power for cesium beam frequency standards. These units we
periodically discharged and recharged as a preventative maintenance
procedure, and they did develop memory. The fix was to vary the
preventative maintenance discharge time/amount. H/P factory support
helped us solve this problem. Doug K7ABX

I remember that in HP freq standards, too, Doug.

What lab do/did you work in? I'm a metrologist, too.

Larry W4CSC

Metrology Engineering Center (Code 132)
Quality Assurance Office
Charleston Naval Shipyard
(may she rest in peace)

In message , taz
writes
I Beg to differ with you.
I have on occasions, and know friends who have damaged
Ni-Cad batteries. They were damaged by partial depletion
then recharging. They were in sealed waterproof torches
and over a period of time the batteries were damaged by
that method of charging. I now always run my batteries from
full to empty no mater what type.
taz.


Top-up charging is the best regime for NiCd's used in a torch. Full
discharge every time simply wears out the cells unnecessarily.

Of course cells vary enormously in quality and it is virtually
impossible to buy decent ones from retail outlets.

--
Keith Lewis

I agree Keith there are a lot of variables to batteries and the way
they are charged. The trouble with most set-ups IMHO is one cell
will fail in the battery and then the battery as a unit starts to perform
badly. Good cells are hard to get hold of and can easily be damaged
by incorrect use. In my experience if a cell is sold with the label good for
2000 charge cycles I've found that, that number can be reduced by half
if not even 3/4. So in real terms a battery that should be good for 2000
charges sometimes only last for 500 maybe 1000 charges.
Not a scientific answer just my own experience.
taz.


Agreed

Cells are extremely variable and the ones on retail sale tend to give
good ones a bad name. Many are in "D" size cases but are only around
1200 mAH as opposed to an average of 4000 mAH for those available to
OEM's

We've been manufacturing NiCd powered lighting for over 20 years and
have been giving a 3 year guarantee for that time. We do however fit
rather good ones:-)
--
Keith Lewis

Agreed

Cells are extremely variable and the ones on retail sale tend to give
good ones a bad name. Many are in "D" size cases but are only around
1200 mAH as opposed to an average of 4000 mAH for those available to
OEM's

We've been manufacturing NiCd powered lighting for over 20 years and
have been giving a 3 year guarantee for that time. We do however fit
rather good ones:-)
--
Keith Lewis

If I need NiCad cells now I use the ones that power
emergency lights. They come pre-made into batteries
and do seem to be of higher quality.
taz.

In message , taz
writes
Agreed

Cells are extremely variable and the ones on retail sale tend to give
good ones a bad name. Many are in "D" size cases but are only around
1200 mAH as opposed to an average of 4000 mAH for those available to
OEM's

We've been manufacturing NiCd powered lighting for over 20 years and
have been giving a 3 year guarantee for that time. We do however fit
rather good ones:-)
--
Keith Lewis

If I need NiCad cells now I use the ones that power
emergency lights. They come pre-made into batteries
and do seem to be of higher quality.
taz.


They tend to be "high temperature" versions (gets warm in emergency
lighting luminaires) so separator design has to be good. Dendritic
crystal growth through separators is the usual failure mode of Nicd's


--
Keith Lewis