On 4/15/2013 4:59 PM, Bill Dube wrote:
"Stale charge" has been known to folks that test batteries for a long
time. The "memory effect" is just a specific manifestation of stale
charge. _Every_ type rechargeable battery has this characteristic. It is
just a matter of degree. In NiCads, it happens to be a very significant
drop in specific power when you go beyond routine SOC and try to access
seldom used charge. Thus, ni-cads are said to have "memory effect".
If you continue to (gently) discharge ni-cads (or other cells) beyond
the boundary of the memory, then you erase the "memory". Like magic,
everything works like it used to.
To be sure, the nicad "memory effect" is largely an old wives tale. It
used to occur in nicads built in the 60's and 70's if you cycled them
with an extremely consistent charge/discharge pattern.
For example, suppose you have a voltage cutoff circuit that *always*
stops your discharge at 50% state of charge (1.1v). You'll find that the
first time you go below this point, the cell voltage immediately drops
from its usual 1.1v to 1.0v as if it is "dead". But if you ignore the
lower voltage and keep going to (say) 0.9v, all your amphour capacity is
still there. -- just at a slightly reduced voltage.
The memory effect is erased by even one full discharge cycle. It also
won't be seen if don't consistently cycle to the same depth of discharge
every time.
Finally, the effect has largely been eliminated in all nicads
manufactured after the 1970's, by changes in the cell design.
It lives on in marketing claims, however. :-)
--
You never change things by fighting the existing reality. To change
something, build a new model that makes the existing model obsolete.
-- Buckminster Fuller
--
Lee A. Hart, http://www.sunrise-ev.com/LeesEVs.htm
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