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

[<daveb seanet com>]

thanks for the clarification.  I can see that I've erred several times by 
not 
plugging in immediately after each use.  

this brings up two more questions.
  
  1.  what do you measure to determine 50% of capacity?  pack voltage? Can 
you 
determine this point by the fuel gauge reliably?  Also I have heard an 80% 
soc 
figure tossed around as in never go below 80% ???

  2.  Are de-sulfating chargers totally bogus?   Has anyone proven to 
their 
satisfaction that they do work in certain situations?

thanks,
dave
E12S
Seattle

> 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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