paul dove via EV wrote:
Equalizing batteries is a process designed to de-sulphate lead acid battery
plates by carrying out a controlled overcharge.
Close; but not quite right.
"Equalizing" refers to bringing each cell in a series string to the same
level of charge. It applies to *all* types of batteries.
The individual cells in a battery are inevitably slightly different.
Even if they are identical twins at birth, they will still age
separately and gradually become distinctly different individuals.
"Equalizing" is when you deliberately charge or discharge some cells
more than the others, to bring them back to the same state of charge.
The goal is to keep one cell from going dead, or reaching full charge
before the rest, which would damage it and shorten its life.
With most battery types except lithium, you can slightly overcharge the
cells to equalize them. The cells that reach "full" first get slightly
overcharged while the lower ones are catching up. Done in moderation,
this doesn't hurt the battery.
With lithium, *any* overcharging degrades the cells and increases the
risk of damage and fires.
Battery plates tend to acquire a sulphate coating over time which
then hinders the chemical action between the electrolyte and the plate.
"Sulphation" only applies to lead-acid batteries. It's mostly an
imprecise marketing idea, made up to sell you stuff. Every lead-acid
cell converts lead and sulfuric acid into lead sulfate when you
discharge it. This lead sulfate is converted back into lead and sulfuric
acid when you charge it. It's not a problem; it's *normal*. Charging
*is* "desulfating" it.
But if you run a lead-acid cell completely dead, it converts *all* of
the acid into lead sulfate. The lead sulfate that completely covers the
plates is a poor conductor, and water is even worse; so you can't charge
it. You've destroyed the battery.
Sometimes, if it isn't completely dead, and hasn't sat that way for too
long, you can force-charge it by applying a higher-than-normal voltage
for longer-than-normal to force current through the cells. Hopefully,
this will start converting a little lead sulphate into lead and acid,
which opens up some pores in the plates, and improves the conductivity
of the electrolyte. Sometimes, you can recover part of the battery's
capacity this way. But the battery is likely to have much lower
capacity, and only be good for a brief time (like a few seconds to start
an ICE).
An entire industry has evolved to sell expensive "desulfators" (which
are just ordinary battery chargers that apply a higher voltage) to
"save" your ICE starting battery.
By equalizing the battery in this controlled overcharge the outer layer of the
plate, including the sulphate coating, is blown off
You do *not* want to "blow off" this sulfate. It holds the lead and acid
that makes the battery work. If the sulfate falls off the plates, it
either drifts to the bottom where it represents lost amphour capacity;
or it lodges between the plates, where it can warp or short them out.
Either case is bad for the battery.
Holding a Lithium battery above it's OCV for long periods of time is
damaging to the cells.
I agree with this. A higher voltage and current into a fully charge
lithium cell will only harm it.
Lee Hart
--
There is a computer disease that anybody who works with computers knows
about. It's very serious, and interferes completely with your work. The
trouble with computers is that you 'play' with them! (Richard Feynman)
--
Lee Hart, 814 8th Ave N, Sartell MN 56377, www.sunrise-ev.com
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