Re: (ET) battery desulfation

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

I recognize that some people, including some pretty knowledgable ones, 
have reported anecdotal positive results from electronic desulfators. I'm 
continuing to watch for carefully gathered evidence that confirms the 
anecdotes, but so far I'm not entirely sold on electronic desulfators.

One reason is that sulfation is, by definition, irreversible.  Once lead 
sulfate crystalizes and sheds from the plates of a battery, there is no 
way, electrically, chemically, or otherwise, to return it to the plates.  
The sulfation represents irretrievably lost capacity in one or more 
cells.  It can be caused by chronic undercharging.

That said, I would like to quote here some comments on sulfation and 
battery aging from Nawaz Qureshi, a senior electrochemist at US Battery.  
Nawaz also worked for many years at Trojan Battery, and is a frequent and 
valued contributor to the EV discussion list.

-- begin quoted text --

1. Normally, batteries do not fail from sulfation. They fail from the 
positive grid corrosion, but primarily from the positive plate active 
material (lead dioxide) shedding. The loss of this material means loss of 
capacity.

2. The positive plate loses its integrity by cycling: the crystal 
structure gets destroyed, a little bit at a time, until the particles get 
so small that they float away from the plate forming the sludge at the 
bottom of the cell.

3. During charge, when the lead dioxide particles, floating around in the 
acid, touch the negative plate, they convert (plate out) into lead metal 
dendrites which grow towards the positive plate, eventually creating a 
short. This is also called mossing.

4. During discharge both of the electrodes (lead dioxide and spongy lead)
convert to lead sulfate, reversing upon re-charge. So  lead sulfate
formation is a necessary condition for the battery to function.

5. If you let a battery sit for 6 months or more, the self discharge 
reactions occur very slowly, forming very large lead sulfate crystals. 
Since lead sulfate is an electronic insulator, they do not convert 
(recharge) easily. This rather pathological condition is called 
sulfation. Normal operation of the battery should not and does not cause 
this condition unless you operate your batteries in significantly 
undercharged condition (mismatched charger?).

-- end quoted text --

In short, unless you allow your batteries to sit unmaintained for many 
months at a stretch, or unless your charger's output is much too low, 
sulfation is not as much of a problem as it's made out to be.  (This was 
news to me too.  For many years I believed what I'd read -- that 
sulfation was the main cause of lost capacity.)

If you have one or more undercharged cells, that will limit your 
available battery capacity.  It or they can be brought up to the highest 
possible level of charge by equalization, restoring capacity.  

I believe that cell equalization is the principal benefit of electronic 
desulfators.  However, it's actually a byproduct of the way they're used. 
It could be accomplished just as well without them by performing a long, 
slow equalization charge.

By the way, one very aggressive maker of electronic desulfators made an 
attempt to sell his product on the EV discussion list several months ago. 
 The result was that the list nominated a member to buy some and test 
them thoroughly.  

Suddenly, the manufacturer stopped posting to the EV list.  When last I 
heard, the manufacturer still hadn't shipped them to the tester.  The 
tester reported that he claimed that he wanted to wait until his "new, 
improved model" was ready.  


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
= = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = =
Thou shalt not send me any thing which says unto thee, "send this to all 
thou knowest."  Neither shalt thou send me any spam, lest I smite thee.
= = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = =