Laptop battery Memory effect

[Weinberger Hans]

Hello everybody.
I just changed my Laptop battery pack as the older battery pack would
recharge for around 5 minutes then stop. I could then use my computer
for a few minutes then it would switch off.
The curious thing is I after opening the laptop batteries they all
seem to be showing the right voltage. It seems that these NiMH are
showing memory effect. Does anybody know of a good way to discharge
them apart from a resistor. If a resistor what should its resistance
be.
The voltage reading inside the battery pack of each cell is around
1.27V.
Till later.
Hans

 

[Dan H]

Hello everybody.
I just changed my Laptop battery pack as the older battery pack would
recharge for around 5 minutes then stop. I could then use my computer
for a few minutes then it would switch off.
The curious thing is I after opening the laptop batteries they all
seem to be showing the right voltage. It seems that these NiMH are
showing memory effect. Does anybody know of a good way to discharge
them apart from a resistor. If a resistor what should its resistance
be.
The voltage reading inside the battery pack of each cell is around
1.27V.
Till later.
Hans

I don't believe NiMH batteries have memory effect. They are only good
for a certain number of charges. I suspect that is what has happened in
your case. The voltage will read good when charged but the amount of
energy stored is small.

 

[Meindert Sprang]

This appears to be a controversial subject and yet some NiMh
manufacturers claim that they do exhibit a memory effect. I hear
dendrites form in the cells when used for a long time that inhibit
proper charge flow.
Still don't know how to discharge the things. Have you any ideas?

Google for NiMH memory effect and you'll find all the answers you need (and
you don't want to hear).

Meindert

 

[Weinberger Hans]

I don't believe NiMH batteries have memory effect. They are only good
for a certain number of charges. I suspect that is what has happened in
your case. The voltage will read good when charged but the amount of
energy stored is small.

This appears to be a controversial subject and yet some NiMh
manufacturers claim that they do exhibit a memory effect. I hear
dendrites form in the cells when used for a long time that inhibit
proper charge flow.
Still don't know how to discharge the things. Have you any ideas?

Hans

 

[Weinberger Hans]

The voltage will read good when charged but the amount of
energy stored is small.

The problem is as I mentioned earlier you can hardly get any
charge to the cells. The laptop signals when the batteries are being
charged ... This happens only for a few minutes as said above . Then
charging stops.

Hans

 

[Leon]

I don't believe NiMH batteries have memory effect. They are only good
for a certain number of charges. I suspect that is what has happened in
your case. The voltage will read good when charged but the amount of
energy stored is small.

And NiCds only exhibit a 'memory effect' in *very* rare circumstances,
mainly in satellite applications.

Leon

 

[Weinberger Hans]

And NiCds only exhibit a 'memory effect' in *very* rare circumstances,
mainly in satellite applications.

Leon

Nope.
Try
http://www.buchmann.ca/chap10-page1.asp
NiMh do exhibit "Memory effect".
Hans

 

[Ian Stirling]

Hello everybody.
I just changed my Laptop battery pack as the older battery pack would
recharge for around 5 minutes then stop. I could then use my computer
for a few minutes then it would switch off.

Over time, the NiMH cells will increase in internal resistance, and fail
to deliver enough current to the load.
What I would do, is to take a .1C load (if 2Ah, 200mA), and discharge
until the lowest cell voltage falls below 1.1V. (MONITORING EACH CELL!)

This can in some circumstances, if done repeately, then charged, have a
small to medium effect on charge life.

 

[Leon]

Nope.
Try
http://www.buchmann.ca/chap10-page1.asp
NiMh do exhibit "Memory effect".
Hans

That's hardly an authorative source. I'd rather go by what battery
manufacturers say, in their literature.

Leon

 

[Weinberger Hans]

That's hardly an authorative source. I'd rather go by what battery
manufacturers say, in their literature.

Leon

The author is the founder of Cadex a world leader in the design and
manufacture of battery analyzers and chargers, but if you believe more
in Battery manufacturers I'll give you 1 example, Sanyo a
manufacturer of Laptop NiMh cells
It says the Memory effect exists in NiMh cells over here
http://www.sanyo.com/batteries/pdfs/twicellT_E.pdf

Hans

 

[Leon]

The author is the founder of Cadex a world leader in the design and
manufacture of battery analyzers and chargers, but if you believe more
in Battery manufacturers I'll give you 1 example, Sanyo a
manufacturer of Laptop NiMh cells
It says the Memory effect exists in NiMh cells over here
http://www.sanyo.com/batteries/pdfs/twicellT_E.pdf

Hans

I think they have it wrong, they are talking about ''voltage
depression' which is a totally different phenomenon. As I said, true
memory effect only occurs in very rare circumstances.

Leon

 

[Weinberger Hans]

I think they have it wrong, they are talking about ''voltage
depression' which is a totally different phenomenon. As I said, true
memory effect only occurs in very rare circumstances.

Leon

LMAO .
First a founder of a worldwide leading Battery charger /analyzer
company is considered dumb by you, now Sanyo Corporation do not
understand what the memory effect is.

Thats actually bad quality trolling.

exskimos

 

[René]

Hello everybody.
I just changed my Laptop battery pack as the older battery pack would
recharge for around 5 minutes then stop. I could then use my computer
for a few minutes then it would switch off.
The curious thing is I after opening the laptop batteries they all
seem to be showing the right voltage. It seems that these NiMH are
showing memory effect. Does anybody know of a good way to discharge
them apart from a resistor. If a resistor what should its resistance
be.
The voltage reading inside the battery pack of each cell is around
1.27V.
Till later.
Hans

Dendrites were mentioned earlier. They usually cause a discharge
resistance that slowly draws more current over time. This usually
happens in an uneven way in separate cells, causing some cells to be
normally charged, while others almost fail to charge, and quickly
discharge. Delta peak load termination dismally fails in this case. Or
the temp shutoff terminates the charge, or the battery management
system senses something wrong.

This internal discharge phenomenon is widely misinterpreted as "memory
effect", while it is just an "end of life" effect. A well used battery
pack may be worn out after roughly 2 years, while some survive much
longer - all it takes is one cell to go bad prematurely.

Unloaded the cells may show normal voltages (per cell) directly after
charging. Charge it - check after a few hours and see what's left.
Some cells will still do OK, others may be deflated considerably.

 

[Frithiof Andreas Jensen]

Weinberger Hans wrote:

LMAO .

Be careful, you could loose what goes for your head!

First a founder of a worldwide leading Battery charger /analyzer
company is considered dumb by you, now Sanyo Corporation do not
understand what the memory effect is.

Thats actually bad quality trolling.

exskimos

You being the Troll boy ... you disagree with what "Leon" wrote; why
misquote it also? To appear more stoopid??

Yersee:

Normal People do not care about exotix like the mythical "memory effect"
enough to discuss it, they just buy a NEW battery pack and SOLVE the actual
problem - presumed to be "the computer not working without the charger"
instead of running around trying to pick an argument, which is what Trolls
do.

Batteries wear out; but, by all means, *do* tinker with the batteries and
fry your laptop (preferably when it is actually sitting on your lap to the
benefit of the gene pool)!

 

[Weinberger Hans]

You being the Troll boy ... you disagree with what "Leon" wrote; why

"memory effect"
enough to discuss it, they just buy a NEW battery pack and SOLVE the actual
problem - presumed to be
do.

with the batteries and
fry your laptop (preferably when it is actually sitting on your lap to the
benefit of the gene pool)!

Your English sucks too much to qualify for a reply.

Hans

 

[Leon]

LMAO .
First a founder of a worldwide leading Battery charger /analyzer
company is considered dumb by you, now Sanyo Corporation do not
understand what the memory effect is.

Thats actually bad quality trolling.

exskimos

This is what Saft says:

Do nickel-cadmium batteries for telecoms exhibit the memory effect ?

The memory effect is a reduction in capacity of a Ni-Cd battery, which
occurs after the battery has been subjected to repeated shallow
discharges.
Memory was an issue only with the first generation of sealed Ni-Cd
cells, and relates to the way in which they are charged. Telecom Ni-Cd
batteries are comprised of vented or flooded cells which do not exhibit
memory effect.
"The so-called memory effect has been a problem with nickel-cadmium
batteries in some applications. Pocket, fiber and plastic-bonded plate
cells do not show this tendancy."

Here is a good description I found of voltage depression:

Ni-Cads have an undesirable characteristic that is caused by
constant overcharge and no, or infrequent, discharges, as
in standby applications. It is technically known as
"voltage depression" and commonly, but erroneously, called
"memory effect". This characteristic is only detectable when
a full discharge is performed. Thus, it is possible to believe
a full charge exists, while in fact it does not.

I'd trust what Saft says; where I used to work we used their batteries
exclusively for critical military applications. Sanyo does seem rather
confused about the phenomenon.

Leon

 

[Frithiof Andreas Jensen]

Your English sucks too much to qualify for a reply.

Hans

Well - you just suck bum-boy
.... and you don't qualify either!

 

[Weinberger Hans]

... and you don't qualify either!

OK I get your problem.
Try hitting your head as hard as you can against a wall. If that
doesn't work use a hammer on it.
If that still doesn't work try writing on alt.drugs.psychedelics .
Good luck.
Hans

 

[Weinberger Hans]

This is what Saft says:

Do nickel-cadmium batteries for telecoms exhibit the memory effect ?

The memory effect is a reduction in capacity of a Ni-Cd battery, which
occurs after the battery has been subjected to repeated shallow
discharges.
Memory was an issue only with the first generation of sealed Ni-Cd
cells, and relates to the way in which they are charged. Telecom Ni-Cd
batteries are comprised of vented or flooded cells which do not exhibit
memory effect.
"The so-called memory effect has been a problem with nickel-cadmium
batteries in some applications. Pocket, fiber and plastic-bonded plate
cells do not show this tendancy."

Here is a good description I found of voltage depression:

Ni-Cads have an undesirable characteristic that is caused by
constant overcharge and no, or infrequent, discharges, as
in standby applications. It is technically known as
"voltage depression" and commonly, but erroneously, called
"memory effect". This characteristic is only detectable when
a full discharge is performed. Thus, it is possible to believe
a full charge exists, while in fact it does not.

I'd trust what Saft says; where I used to work we used their batteries
exclusively for critical military applications. Sanyo does seem rather
confused about the phenomenon.

Leon

Thanks for the quote. I will send some more interpretations on the
subject if you are interested later.
As I said earlier the memory effect is a controversial subject , IMO
saying that one side is right wheras the other is wrong is sticking
ones neck out. Hey everyone has his own viewpoint and a right to judge
things based on his own experience, sensations etc.

Hans

 

[Joseph2k]

And NiCds only exhibit a 'memory effect' in *very* rare circumstances,
mainly in satellite applications.

Leon

Actually there are techniques to prevent / stop memory affect and satellites
use them with a vengeance. Memory effect in not so much rare as rather
specific conditions, it has happened to me and others i know. Fortunately
there is a solution, forcibly deep cycle them.