Hi Jim
On (23 Oct 97) Jim Dunmyer wrote to Alec Cameron...
 JD> I've found that my big RV/trolling batteries on the UPSs here don't seem
 JD> to hold up at all well. IE: a couple of years and they're done. It 
finally
 JD> dawned on me the the charger in the UPS is voltage limited to a low 
enough
 JD> value that the batteries will have to be equalized now and then.
Back in the 1980s I was part of a project team looking at poor capacity and
cell failures, in large lead acid cells- 4000 AH. I had a bee in my bonnet
that the makers, and my employer, would not agree to react to. Here was
my theory-
Acid batteries that were charged from dynamos [ie steady DC] seemed healthier
than those charged by thyristor chargers [ie pulsating DC]. I therefore 
guessed,
that the inductance [hence the series reactance, so called "AC resistance"]
due to the geometry of the bus work within each cell, was causing exceptional
volt drop within the cells, so that even if the plates were gassing nicely
uniformly near the main terminals, there could be areas of the active plates
that were getting less of the recharge energy. I was especially annoyed that
the maker had used steel bus work both above and below acid level, the
steel being jacketted in lead.
Steel being magnetic, would cause much greater inductance in the charging
circuit.
 JD> Interestingly enough, the gel-cell type batteries that are OEM in those
 JD> UPSs don't seem to need this treatment to hold up for several years.
 JD> They'll usually go 3-5 years without replacment.
Gel types have weird chemistry in that the positive and negative plates are
very unequal in amp hour capacity ie there is too much active material in one
polarity- I forget whether it is the + or the - side.
The effects of this are-
        * very little water loss occurs upon over-charging
        * it is very hard to "overcharge" gel cells because the internal
        voltage will rise easily whereas a liquid filled battery will resist
        overcharge, the volts holding down and the current able to reach a
        damaging high value.
These curious responses of the gel type, protect it from early failure. BUT! 

don't think a gel cell can deliver the huge oomph required by the largest
engine starters. Yes gels are used for engine starting, but a wet cell 
attery
for much lower cost, will start it even quicker.
Cheers.....ALEC
... ******FLASH! Energiser bunny arrested, charged with battery******
--- PPoint 1.92
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