Date:         Thu, 20 Apr 1995 11:23:57 -0700 (PDT)
Sender:       Vanagon Mailing List <vanagon@vanagon.com>
From:         Alistair Bell <ui775@freenet.victoria.bc.ca>
Subject:      Re: Speaking of batteries...



On Thu, 20 Apr 1995, 7039ckrah@umbsky.cc.umb.edu wrote:

> In response to Alistair's question on the EDTA use in batteries, my GUESS
> is that the EDTA functions as a chelator for all divalent ions.  EDTA has

As far as I know, it is only a chelator of divalent cations

> been used to reduce the activities of metals in solution (Activity refers
> to the free ion concentration) In lead acid batteries, the lead exists as
> Pb+2 when it is in solution.  Maybe adding EDTA complexes the Pb+2 such that
> it doesn't react and form the slightly insoluble sulfate salts

But the sulfates are part of the reaction.
Its when the sulphate formation upon discharge is not completely reversed
upon charging, and some sulfate remains, you have problems. I'm guessing
that deep discharge will create a thicker sulfate layer which is harder to
completely solubilize on charging, thus "sulfating" the battery. A good
reason for not dischaging the battery below 80% of max capacity. A deep
cycle battery, aswell as having thicker plates, has more room below the
bottom of the plates for any sloughed-off sulfate to lie and not bridge
the adjacent plates.

BTW I mis-spoke :), EDTA is an acronym for ethylene-diamine-tetra-acetic acid
not the daft ethylamine-diamine-tetra-acetic acid.

Alistair