RE: (ET) batteries (sulfating and self-discharge)

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

I may have confused positive grid corrosion with sulfating.  If so, I'm
sorry.  I thought I 
described the mechanism as it was described to me by an 'expert'.  I was
told the crystal form 
only occurred when the battery was left totally dead.

Larry Elie


-----Original Message-----
From: David Roden (Akron OH USA) [mailto:roden ald net]
Sent: Friday, April 11, 2003 3:49 PM
To: elec-trak cosmos phy tufts edu
Subject: Re: (ET) batterys (sulfation and self-discharge)


On 11 Apr 2003 at 15:01, Barry Woods wrote:

> improper recharging can cause sulfating of the
> batteries. 

Correct.  But IMO sulfation is not as common a failure mechanism as is 
usually thought.  It's a pathological condition that results from a 
failure 
to recharge promptly after using the batteries, from long periods of 
disuse,

or from chronic undercharging.

Understand that lead sulfate formation is normal.  It forms as the battery 
discharges, but the lead sulfate is almost 100% reconverted to lead by the 
chemical reaction of charging.  However, if the battery sits in a 
discharged

state for several months, or if it self-discharges over a period of a year 
or more, the lead sulfate crystals that form on the plates become larger 
than normal because of the very slow discharge reaction.  These are harder 
to reconvert to metallic lead during charging, and are more likely to 
break 
off, than the smaller crystals formed in normal use.

Some people swear by them, but I find no verifiable scientific evidence 
that

the expensive "pulse desulfators" do anything more for the battery than 
simple low current equalization charging would do.  Personally, I think 
they're a waste of money.  But as I say, some people obviously don't agree 
with me.

Using your ET and then forgetting to recharge the batteries is definitely 
not a good thing.  Letting it sit over the winter is not as bad.  In 
general

self-discharge is not a problem for a battery only a year or so old; it 
can 
sit for 4-6 months uncharged, untouched, and unloved withou suffering much.

However, self-discharge increases as a battery ages, so some kind of 
maintaining scheme becomes more appropriate after, say, 2-5 years of 
battery

use.  

A float charger is essentially a regulated constant-voltage charger 
operating at float voltage (2.2 volts per cell).  But Harry Landis's 
controller is not a float charger.  Instead, it monitors the battery 
static 
voltage and turns on the ET charger for 5 minutes if it drops below a 
certain point (default is 38 volts).  

Some people use them and seem to like them.  The Landis controller appears 
to be useful if you have old batteries and let your tractor sit for weeks 
or

months at a stretch.  IMO you don't need one if your batteries are fairly 
new, or if you can remember to plug in the charger for a quarter-hour or 
so 
once a month.

In regular use, chronic undercharging is seldom a problem with ETs.  
Unless 
you have a problem with the capacitor, the GE charger generally errs on 
the 
side of overcharging.  

So do most chargers.  IMO more batteries are killed by overcharging than 
by 
undercharging.  Overcharging causes positive grid corrosion.  The most 
obvious symptom of this is battery case swelling.  I have a few old 
batteries so badly afflicted by this that their positive posts are 
actually 
pushed upward 3 or 4 mm.  These batteries are good only for use in the 
weight box. 


David Roden - Akron, Ohio, USA
1991 Solectria Force 144vac
1991 Ford Escort Green/EV 128vdc
1970 GE Elec-trak E15 36vdc
1974 Avco New Idea 36vdc
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