NiCAD Memory Effect

[Sir Spamalot]

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

 

[Glenn Ashmore]

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.

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

--
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

 

[Ed Price]

Because you leave them on simple trickle chargers long term, which causes little
whisker crystals called dendrites to form inside the battery and short it
out internally. I get a heck of a lot of recharge cycles out my rechargeables.
I use smart chargers that just about shutdown (go way below "trickle") when
the battery is charged.

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

 

[Sir Spamalot]

OK, so there's no memory effect. But, why do I have to regularly change out
the rechargeable batteries of my cordless phones, dustbuster, laptop,
electric toothbrush, flashlight, ect.?
1,000 recharge cycles? ........rubbish!

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

 

[Chuck Tribolet]

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
[email protected]
http://www.almaden.ibm.com/cs/people/triblet

Silicon Valley: STILL the best day job in the world.

 

[Ed Price]

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