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Laptop battery Memory effect

Discussion in 'Electronic Design' started by Weinberger Hans, Mar 15, 2006.

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  1. 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
     
  2. Dan H

    Dan H Guest

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

    Meindert
     
  4. 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
     
  5. 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
     
  6. Leon

    Leon Guest

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

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

    Ian Stirling Guest

    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.
     
  9. Leon

    Leon Guest

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

    Leon
     
  10. 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
     
  11. Leon

    Leon Guest

    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
     
  12. 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
     
  13. René

    René Guest

    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.
     
  14.  

  15. Your English sucks too much to qualify for a reply.

    Hans
     
  16. Leon

    Leon Guest

    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
     
  17. Well - you just suck bum-boy
    .... and you don't qualify either!
     
  18. 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
     
  19. 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
     
  20. Joseph2k

    Joseph2k Guest

    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.
     
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