Hi Roy
On (28 Aug 96) Roy J. Tellason wrote to Alec Cameron...
 RJ> This is true.  I have seen it on one or two occasions,  mostly a rather
 RJ> muddy-looking sludge,  but often it's not very visible,  perhaps being
 RJ> caught in the separators...
That would be the reason for separators overlapping the plates, to extend the
leakage path.
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 RJ> One would hope so.  I wonder how you'd get a charger to determine
 RJ> whether
 RJ> a battery was either severely discharged or had a shorted cell, 
 RJ> though?
It could be done but I doubt that anyone would take the trouble, given the
availablity of qualified service staff. A Smart charger could be designed to
evaluate dV/dT ie the time rate of voltage rise and compare this with the
terminal volts at that moment.
 AC> cell conductance. At a generating station I worked in we had a 
 AC> few single cell chargers, so that in-service diagnosis and 
 AC> correction was possible on individual cells weighing several 
 AC> hundredweight.
 RJ> Yeah,  but that's not going to help much with what I've got here.  
ithin
 RJ> this small office at the moment are two group 27 deep cycle batteries, 
 RJ> two 6v/33ah gels,  and four 6v/12ah gels.  No way to test individual 
cells
 RJ> on those except a hydrometer (one of those is handy too),  but I was
 RJ> thinking more along the lines of some way for a "smart" charging circuit
 RJ> to be able to tell when it was a lost cause...
You have an embarrassment of riches. You are doomed to either keep a log of
each one and give it tender loving care, or to neglect same in the usual way
and buy solutions to the inevitable problems!
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 AC> drops. The resistance of internal busses is significant. Some 
 AC> are of copper clad with lead! Not a well known fact. 
 RJ> That could get interesting if the lead coating were breached,  and may
 RJ> well explain why so many of the failures I saw were "bad connections"
 RJ> where you could see a full charge on all of the cells with a hydrometer
 RJ> but couldn't pull any significant amount of power out of it.  Something
 RJ> inside had gotten to a very high level of internal resistance.
I have seen an internal [submerged] bridge in a city phone exchange battery,
corroded almost right through. The possible effect of an open circuit while
passing current [eg on boost charge] bears sober thought!
The copper or brass inserts were a commercial solution to meeting a severe
duty cycle ie maintaining output voltage during overload. Cheaper to
use copper than to add more active plates!!
                                           
 AC> Resistive internals, results in full charge being acquired near 
 AC> the cell terminals, before it "penetrates" in to the larger 
 AC> amounts of more distant plates. Important I think with foil 
 AC> constructed cells eg nicads.
 RJ> I wonder how much this applies to the stuff I've got here,  though?
Yes to some degree but we'll never know how important. The "linear" 
ifference
in charge state for material nearest to the terminals vs material more
distant, is potentially a sinister factor because "local" cells can be set up
on the path of a single polarity. With a potential drop along the lead path
[eg of the positive assembly] current will flow thru the acid stripping lead
[or paste] from the more positive areas and depositing onto the less positive
areas. On that basis, fast charging is bad news and slow charging is good
news. These are fundamental topics, you can bet! that the old designers get 
t
right, but it is quicksand in the path of a new product designer.
 AC> ........................................................... Me, I just
 AC> go to K-MArt and buy the largest battery that can be fitted in 
 AC> the engine bay.
 RJ> 
 RJ> So do I,  but mostly because you can get the same CCA rating in many
 RJ> different sized packages,  but a bigger box is going to have more 
eserve
 RJ> power.  What's a litle surprising when you look at those charts long
 RJ> enough is that there are some 4-cylinder motors which require _more_ CCA
 RJ> than the 6 cylinder or V8 engines in the same car in the same year.
A high CCA rating in a small package is costly and hi tech and I admire the
skill of the makers. But a penalty is that the QA needs to be tighter-
clearances inside are more critical, separators must perform better etc. I
prefer the big conservative designed product. 
I think some auto makers select a battery without sound technical study. 
aybe
they get a a good offer from a battery maker and if the application looks
carzy, they may get away with it by using the smaller batteries for models ex
factory at winters' end!
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 AC> Severe vibration, 
 RJ> I notice that they sell different batteries for "stationary" 
applications.
Yes, partly because the user expects a long life. The old Plante batteries
were good for about 20 to 30 years, I doubt if these are still made. Where I
worked we were finding difficulty to buy these in about 1980. A battery with
that life expectancy, was not good for business!
 AC> excessive charging especially of a "full" battery are
 AC> aggressive in removing active material.
 RJ> Sounds like overcharging isn't necessarily a good thing,  then.
Well, it is still necessary say once annually [equalising charge] and is
monitored and stopped in time, the injury done is very slight. Like putting a
heart patient on a treadmill and working him hard under supervision. May do
him the world of good, but there is some wear and tear!!
End of message 1 now I go to your message 2
... FLASH! Energiser bunny arrested, charged with battery.
--- PPoint 1.92
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