Re: Li-Ion life cycle management

On Fri, 23 May 2008 07:32:02 -0700 (PDT), Richard Henry <pomerado@xxxxxxxxxxx>
wrote:

On May 22, 6:40 pm, rebel <m...@xxxxxxxxxxx> wrote:
On Thu, 22 May 2008 07:57:54 -0700 (PDT), Richard Henry <pomer...@xxxxxxxxxxx>
wrote:

On May 22, 4:17 am, JosephKK <quiettechb...@xxxxxxxxx> wrote:
IME Lithium cells, of most technologies, they are intolerant of
overcharge, excess charge/discharge rate, or discharge below 30% of
capacity.
YMMV

Correct on all counts.  That is why it is imperative to use proper chargers and
pack mangement modules for these chemistries, and not improvise.

Decent chargers ensure a controlled current-limited constant voltage charging
regime.

Protection modules integrated into the packs ensure that excess temperature or
low temperature disqualify charging.  They monitor individual cell voltages and
disqualify the pack if these differences exceed a threshold value.  They prevent
discharge below an end voltage which is typically 3v0.  They also (depending on
selection) limit the discharge current allowed.

One of the best descriptions I have found for the proper care and feeding of
Li-Ion cells is in the data*** for the Maxim MAX1737 - a controller we used
several years ago in a commercial charger design.  It is a worthwhile read.

http://datasheets.maxim-ic.com/en/ds/MAX1737.pdf

Does that mean we should discount the advertised capacity figures and
only expect 70% of it in use?

No, quoted capacity is invariably usable capacity down to that cutoff value.

Then saying that the last 30% is unusable is a mis-statement.

Yes and no - it is really semantics. Technically it is usable, but at your own
peril in terms of degradation and subsequent decomposition, which can be
hazardous. But in terms of sensible cyclic use you simply don't go there, and
any pack protection module will prevent it in the interests of saving the cells
to use again.

Have you read the Maxim data *** yet?
.

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