RE: (ET) batteries

["Elie, Larry (L.D.)" <lelie ford com>]

I believe that sulfating occurs ONLY after extended overcharging.  I can't 
foresee any way 
of forcing it to happen other than after significant boil-off.  The 
battery is filled with 
sulfuric acid diluted with water.  If you boil of some of the water, you 
increase the 
concentration of the acid.  As I understand it, if you keep boiling off 
the water, eventually 
the sulfuric has to go somewhere, and the plates are the highest surface 
area thing near by.  

The most common way for this to happen is when you have SEVERELY 
un-matched batteries.  ET 
equalization is done by over-voltaging the whole pack.  'Full' is about 7 
V per battery (6 is 
a nominal value that is really 'low', partially charged).  To equalize, 
the ET charger puts 
an average of 7.3 V or MORE per battery in order to bring any one bad 
actor up, realizing that 
when the charger is off, that 7.3 will drop back down closer to 7 V.  If 
you have one battery 
that can't come up, the rest of the pack keeps climbing, because the 
charger only knows about 
the average.  Look at the 'fuel' or volt meter.  The HIGH section is over 
44V.  That's 7.33V 
each.  If one battery has 'reversed' (gone negative) or is hovering at say 
3V, you would be 
putting 44-3 or 41V across only 5 batteries and each is seeing 8.2V!  Now 
that's extreme, 
because with one battery at 3V the ET charger will probably never be able 
to bring the pack 
to 44V in a reasonable amount of time.  I think GE counted on that.  There 
may be other ways 
of preventing sulfating, but if you are worried about it, make sure that 
near the end of your 
charge cycle that no single battery is getting more than about 7.5 or 
7.6V, for any long period 
of time.

BTW, when using a 'ball' type hydrometer, remember to tap the side of the 
glass/plastic with your 
finger to knock off any air bubble that might be stuck to the ball by 
surface tension.  Air bubbles 
can float a ball that might otherwise sink.

Larry Elie


-----Original Message-----
From: Barry Woods [mailto:barry woods wright edu]
Sent: Friday, April 11, 2003 3:02 PM
To: elec-trak cosmos phy tufts edu
Subject: Re: (ET) batterys


David had mentioned that improper recharging can cause sulfating of the
batteries.  Can David or anyone tell me the proper technique to prevent 
this
from happening.  I just put a new set of batteries in last year and don't
want to trash them.

The GE manual that came with the tractor said that the batteries should be
charged after every use.  I set the charger on 1-2yrs mark everytime I
recharge, which gives about a 14 hour or so recharge time. This seems like
overkill as I only use the tractor for about 40 minutes each time, and the
meter indicates that the batteries are not even down to half-way 
discharged.
Is sulfating from overcharging or undercharging?

What would be the effect of the use of the float charger that one of our
group members sells.  Apparently this is kept plugged in at all times the
tractor is not being  used.  Does this type of charging decrease the
possibility of battery damage to sufating?

Barry
Dayton, OH