Re: (ET) time for a new pack...

["Don Cohen" <bond007d netsync net>]

Good commentary David! I was going to write something on the same lines
after I read what Don wrote about not charging the batteries till they were
fairly discharged, but you beat me to it!
Don C.

----- Original Message -----
From: David Roden (Akron OH USA) <roden ald net>
To: <elec-trak cosmos phy tufts edu>
Sent: Tuesday, August 07, 2001 11:16 PM
Subject: Re: (ET) time for a new pack...


> On 7 Aug 2001, at 12:29, Don Barry wrote:
>
> > As always, the thing to remember is not
> > charge up the batts until they're fairly well discharged.  That's the
basic
> > purpose of the sizing.
>
> I want to clarify this so that no one gets the wrong idea.
>
> Don is correct that you should, if possible, size the battery (choose its
> capacity) so that your usual mowing or other service discharges it about
> 50%.  That's the optimum use of a battery for lowest overall cost per
> amount of work accomplished (in a road EV, we'd say lowest cost per
> mile).
>
> But don't get the idea from this that if you use only 20% of the battery
> capacity to mow your lawn, you ought to charge only every 2 or 3 times
> you mow.  Definitely not!
>
> Lead batteries should be charged immediately after any use that
> discharges them more than a trivial amount, perhaps 10% or even 5%.
>
> The reason for this is that the discharge reaction converts the active
> material (lead and lead dioxide) into lead sulfate.  As this compound
> sits, it crystallizes.  The longer the sulfate remains, the more
> difficult it is for the charging reaction to change it back into lead and
> lead dioxide.  The crystalline lead sulfate breaks away from the plates
> and falls to the bottom of the cells, where (in spite of what the
> "desulfator" salesmen claim) it is for all practical purposes lost
> forever. This process is called sulfation, and it's one reason for the
> loss of capacity as a battery ages.
>
> What's more, the more deeply you discharge before charging, the shorter
> the battery's cycle life will be.
>
> Don is right to the extent that the most economical operation of a lead
> battery is when you use about 50% of its capacity each time.  However, if
> you can't use that 50% in one session, charge it up anyway.  Letting it
> sit uncharged for 24 hours -- even 12 hours -- will negate any advantage
> of using half the capacity this way.
>
>
> David Roden - Akron, Ohio, USA
> 1991 Solectria Force 144vac
> 1991 Ford Escort Green/EV 128vdc
> 1979 General Engines ElectroPed 24vdc
> 1970 GE Elec-trak E15 36vdc
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