Re: (ET) batterys in my I-5

["David Roden (Akron OH USA)" <roden ald net>]

On 10 Apr 2003 at 20:15, D Howell wrote:

> All of them floated 3 balls (75%)
> or more.  About 6 cells out the the 6 batteries
> floated all four balls.  If I assume an average of
> 75%, is this enough to give me very much run time? 
> Since a battery should never be run down below 50%, it
> would make sense that I have about one-half capacity
> of new batterys.  Is this a valid conclusion?

Those testers are so inaccurate as to be worthless.  Throw it away and buy 
a 
good float-type hydrometer.  I think mine is an E-Z-Red.  Even the cheap 
ones from Taiwan and China that they sell at Pep Boys and Autozone are 
better than ball testers.

Most likely your batteries are sulfated.  This means that the lead sulfate 
that forms as part of the chemical reaction on discharge has crystalized 
because the batteries weren't recharged promptly.  Some of it has flaked 
off 
the plates.  It doesn't matter what snake oil you pour in or what 
expensive 
gadget you connect, this stuff will never go back onto the plates.  It's 
lost to the battery forever.

This has two consequences:  First, it causes lost capacity.  Second, the 
lead sulfate precipitate sinks to the bottoms of the cells; if it builds 
up 
sufficiently, it shorts the battery's plates.

First you need to do a load test.  Fully charge the batteries and apply a  
25 to 75 amp load.  You can even use a half-dozen or so car headlights in 
parallel (connected across 12 volts worth).  With the load applied, 
measure 
each battery's voltage.  Any that measure some multiple of 2 volts low 
(meaning one or more shorted or otherwise damaged cells) are probably junk 
and should be replaced.  

If you're really patient, you can try restoring such batteries with a 
separate 6-volt charger, but you'll be hurting the remaining good cells 
trying to charge the dead one(s).  IMO it's not worth the hassle when 
decent 
used batteries are around $20 each and new ones $45 or so.

Beyond that, the only way to tell what you have there is to do a capacity 
test.  Just run the tractor around until the batteries show significant 
weakness.  Recharge.  Repeat several times.  Overcharge (equalize) for 
several hours each time you charge.  With luck, you'll see a gradual 
increase in capacity.  Who knows, it might actually be enough capacity to 
do 
the work you need to do with the tractor.

The 50% rule is not an absolute.  It will give you the most long-term 
range, 
in terms of number of lifetime cycles * distance traveled per cycle.  But 
discharging to 65% won't instantly kill the batteries.  I recommend not 
going beyond 80% discharged, however, because beyond this you begin to 
risk 
cell reversal.


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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