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NiCAD Memory Effect

Discussion in 'Boat Electronics' started by Sir Spamalot, Jun 17, 2004.

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  1. Sir Spamalot

    Sir Spamalot Guest

    Hi all,

    I've seen quite a few posts on this subject, and would like to add my
    $.02.

    About 10 years ago, I was involved in the design of a telemetry device
    that used NiCADs for backup (up to 23 hrs.). I was deeply concerned
    about the charge/discharge of these, so my boss, who was an ex-VP for
    GE, tracked down the NiCAD guru at Gates. When asked about "memory",
    this guru stated, unequivocally, that the "memory" effect was somewhat
    of an urban legend, promulgated by the difficulties NiCADs presented
    when initially developed somewhere around WW2. Modern battery
    manufacturing designs and techniques in the last few decades or so
    have totally eliminated the "memory" effect

    Last I checked, one of these telemetry devices was still running OK,
    even though it was installed over 8 years ago. Granted, I have no
    idea if it's **ever** actually used it's battery backup, but I have to
    assume that sometime in it's life it has been unplugged for at least a
    little while.

    No troll, no flame wars please. I'm just passing on some info.

    SS
     
  2. Well, here is an item that reinforces the myth: My 18V NiCad drill came
    with a charger that has a "Battery Conditioning" button. The
    instructions say that every 6 to 8 recharges I should press the button
    to restore the original capacity of the battery pack. My top of the
    line MaHa NiMh/NiCD charger has a similar button with the same
    instructions. The MaHa/Powerex instructions go on to say that new NiMH
    batteries must go through 4 or 5 complete drain cycles before they will
    store their full capacity and that I could do that by pressing the
    "condition" button. The charger would then drain the batteries before
    starting the charge.

    Sure sounds like a cure for "memory loss" to me.


    --
    Glenn Ashmore

    I'm building a 45' cutter in strip/composite. Watch my progress (or lack
    there of) at: http://www.rutuonline.com
    Shameless Commercial Division: http://www.spade-anchor-us.com
     
  3. Ed Price

    Ed Price Guest


    I believe that, as the crystalline area grows, it obscures the usable plate
    area, which is what causes the "memory" effect. I read some recent research
    (which I now can't find) where new cells were put through a careful charge
    and then a deep discharge cycle. Then, the cells were deliberately
    overcharged. Instant loss of capacity; the "memory" effect instantly
    duplicated. OTOH, another group of new cells were put through many shallow
    discharge cycles, with careful recharging. Result, no memory effect. Then,
    with one overcharge cycle, the memory effect was now there.

    Seems to confirm the concept of "memory", it's just that the culprit is the
    charge profile, not the discharge portion. And that means that dumb
    "trickle" chargers are really cell killers; we need to use smart chargers
    exclusively.

    I wonder if NiMH chemistry shows the same effect?

    Ed
    wb6wsn
     
  4. Sir Spamalot

    Sir Spamalot Guest


    Because the chargers supplied with the consumer grade equipment is
    improperly charging the batteries from the get-go. If they are
    charged **correctly**, and discharged **correctly**, no memory.

    And Larry is also right; the consumer buys into the "rechargable"
    aspect without verifying if the battery is being charged correctly in
    the first place.

    For consumer equipment, I've noticed that overdischarging, which is a
    major cause of failure for any rechargable battery, is ignored.

    Does your dustbuster have an overdischarge shutoff? I bet not.

    SS
     
  5. They may have done the other BAD thing --- over-discharging.
    When you run an NiCD pack DEAD flat, the weakest cell gets
    reverse polarized, and that's death to that cell. One dead
    cell means the pack is kaput.

    --
    Chuck Tribolet

    http://www.almaden.ibm.com/cs/people/triblet

    Silicon Valley: STILL the best day job in the world.
     
  6. Ed Price

    Ed Price Guest

    No, the research was done using single cells, not multi-cell packs. And they
    didn't discharge them to "flat", but rather stopped at something like 5%
    capacity. They wanted a "deep" cycle, but not a deadly cycle.

    Ed
    wb6wsn
     
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