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VK5QX > TECH 14.07.03 16:16l 139 Lines 5125 Bytes #999 (0) @ WW
BID : 760651VK5QX
Read: DB0FHN GUEST OE7FMI
Subj: Re: NICADS (The Truth ?)
Path: DB0FHN<DB0RGB<DB0MRW<DB0ERF<DB0FBB<DB0IUZ<DB0GOS<DB0EEO<DB0RES<ON0AR<
VK6HGR<VK5UJ<VK5BRC<VK5SPG<VK5LZ
Sent: 030713/0631Z @:VK5LZ.#ADL.#SA.AUS.OC #:1440 [Elizabeth] $:760651VK5QX
From: VK5QX@VK5LZ.#ADL.#SA.AUS.OC
To : TECH@WW
MY MEMORY JUST AIN'T WHAT IT USED TO BE.
We have seen recent discussion, and might I suggest "argument", on the
matter of "memory" as far as Nicad batteries are concerned.
For mine, I see quite a bit of what has been said as being somewhat
pedantic. Whether one calls it "memory" or NOT, seems beside the point.
It does not take a rocket scientist knowledge to note that what SEEMS like
a memory is a well recognised fact in the context of the discussion.
"A rose by any other name" etc.
I have observed the claimed memory effect as well as the, sometimes,
spectacular, effects produced by "Zapping" a cell to get rid of the "short
circuits" and frighten the cell back into life.
(Is this anything like the shock treatment used where heart attacks are
concerned?)
For quite some time now John G8NMY has, periodically been providing a
series of interesting bulletins addressed to TECH @ WW.
These have covered a wide range of topics with one of the topics being
"Recovering OLD NICADS".
In this particular bulletin John has included additional comment provided
by G8TBF in which "memory effect" is mentioned.
I wonder whether all the malarky that we have seen is really necessary and
whether people would have been just as well informed by reading and, if
necessary following, the methods suggested in the bulletin from John
G8MNY.
I have appended a copy of the relevant bulletin below.
The recent contributions to the discussion regarding the various types of
charging/discharging units available has been interesting. However, I
rather think that I will continue to follow the time honoured processes
that I have become used to rather than go out and purchase a relatively
expensive piece of equipment.
(I always have my 10,000 mfd capacitor and a suitable power supply handy.)
By the way, if John is reading this message he may be interested to know
that I have retained a copy of most of his technical type bulletins in a
special folder for reference purposes. Thanks John!
Regards,
Ian
__________
73 de Ian, VK5QX
@ VK5LZ.#ADL.#SA.AUS.OC
13 July 2003
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To :TECH @WW
Date/time :12-Jul 22:26
Message # :132472
Title :Recovering OLD NICADS
Path: !VK5LZ!VK5SPG!VK5ASF!VK7AX!WA7V!RZ6HXA!IK1ZNW!GB7CRV!
R:030712/2226Z @:GB7CIP.#32.GBR.EU #:5400 [Caterham] $:5400_GB7CIP
From: G8MNY@GB7CIP.#32.GBR.EU
To : TECH@WW
Old Nicads batterys usually end up with several cells being short circuit,
as they suffer from crystal growth in the electrolyte. To reclaim the cell
before charging, (as charging will not remove the short) a very high
current pulse must be used.
With a sealed battery pack this can blow any internal safety fuse! So it
is
best done when U have opened the pack. The good cells will withstand the
high current OK, but having them in series can reduce the current
depending on how you are applying it, if you have a really bad cell.
Current up to 10xC (eg 5A on a 500mAH AA cell, 40A on a 4AH D cell) can be
safely applied until the pack warms, (how fast chargers detect 70% charge
&
drop back to trickle).
For more difficult cells, current over 10xC may be required, this can
destroy the internal cell wires, but you have nothing to loose! Charge up
a 10,000uF to 40V & connect to cell (computer must not be nearby!) with
thick wires, the 100A pulse usually clears the short after a few pulses.
Once all the cells are over 1V, then trickle charge (Cx0.1) until warm or
14 hours. A few cycles of discharge & charge will bring back old cells to
100%.
If the capacity is less than 100% after a few cycles or there is excessive
volt age (>2V) across a cell when charging, it is O/C or dry & will need
to be replaced.
From: G8TBF@GB7NND.#23.GBR.EU
To : G8MNY@GB7CIP.#32.GBR.EU
Hi John,
Here is a couple more bits of info for your collection:-
Tony, G8TBF says cells going short due to crystallization is not due to
the
electrolyte but the cadmium electrode; cadmium has a property of 'cold
crystallization' (like Tin & Zinc) and can form 'needle' type spikes that
bridge the cell.
The way to prevent this is to occasionally give the cells a long charge at
a low current (<= 10 hour rate). This dissolves any 'needles' and
re-plates the surfaces.
The other effect of the cadmium crystallization is the 'memory effect' -
this happens when cells are not fully discharged for long periods, and is
caused by the 'deeper' parts of the cadmium plate crystallizing.
The effect is that once the amorphous metal on the surface of the plate
has
been dissolved during discharge & the crystalline part is exposed, the
cadmium is much less reactive - a crystalline structure simply does not
break down as easily as amorphous metal.
The cure for 'memory effect' is to deep-discharge the cell, by connecting
(e.g.) a 10 ohm resistor across it and leave it until absolutely dead.
Normal recharging will then give full capacity & no 'memory'.
/QSL
73 De John, G8MNY @ GB7CIP
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