I think the PbSO4 forms crystals rather then spongy deposits that can
re-disolve on the lead plates and reduces the effective surface are of
the plate.  Lower effective area means higher internal resistance.

With any lead acid battery the number of charge/dischage cycles
depends on how far you discharge them.  You can optimize your system
for either low size weight and cost or for "greatest number of amp
hours removed from the battery over it's lifetime"  The two goals are
in conflict.

Almost all the methods people use to "fix" a LA battery that no longer
holds a charge don't work so well.  If the battery did not have a long
enough service lit it's best to buy a replacement that is rated with
more amp hours.  Don't buy a gel cell unless yu really do need to use
it's ability to operate in all orientations, upside down and such.  If
it will stay upright a sealed, flooded battery will give better
performance.

--

Chris Albertson
Redondo Beach, California

Basically, it is a matter of thickness, and the quality of an insulator.

All lead acid cells work essentially the same:  A lead oxide electrode
immersed in sulfuric acid converts to lead sulfate when power is drawn from
the cell.  Lead sulfate is a very good insulator when it gets thick enough.

So, as the cell discharges, a lead oxide layer builds on the plates.  When
the lead sulfate gets thick enough, it insulates the remaining lead oxide
from the current flow, and the cell is discharged.

When it comes time to recharge the cell, you apply voltage, and if the
sulfate layer is still thin enough, current will be drawn, and electrolysis
action will commence, and the lead sulfate will be turned back into lead
oxide, and sulfuric acid.

If you let the dead cell sit around before recharging it, the lead sulfate
will have a chance to convert even more of the lead oxide to sulfate, and
the layer will grow thicker, and thicker, and become a better and better
electrical insulator.... To the point where the lead plates are completely
isolated and no current can pass.... The cell is ruined.

One way you can sometimes resurrect a cell in this ruined condition is
to apply a high voltage, with a low current limit to the cell.  This will
get some current flowing, and will convert, albeit slowly, some sulfate
back to lead oxide and sulfuric acid.

Such repairs take weeks, or months, to work, and have a great risk of
forming current hot spots which will physically destroy the plates.

Others say that applying a stream of short, high voltage pulses, to the
cell will break down the sulfate's insulation ability, and let the
electrolysis action commence.

Either method will work, somewhat.  And only on a cell that isn't too
far gone in the first place... eg. a cell that has only been dead for
a week or two.

-Chuck Harris

Robert Roehrig wrote:

Robert wrote:

As others have explained, the problem is sulfation.  I have had good
results de-sulfating lead-acid batteries of all types (flooded, gel,
AGM) with "BatteryMINDer" brand chargers/desulfators.  With badly
sulfated batteries, rejuvination can take a long time.  Often, they
return to a good approximation of "like new" performance.  Sometimes
they improve but don't return to "like new."

http://www.batteryminders.com/batteryminder-model-1500-12volt-1-5-amp-maintenance-charger-desulfator/

Best regards,

Charles

Hi Robert:

I've spent a lot of time charging batteries using different methods and on various chemistries.

When the charge is in the form of a pulse, ideally including a reverse polarity pulse, the charge is more effective.
This is also a way to sometimes, but not always, will recover a battery that otherwise will not take a charge from a DC
source.

I think this works because it takes some time for chemical reactions to work and by using a pulse you can force the
reaction to a higher level that you can't do using DC without causing problems such as boiling the electrolyte.  For
more info see Burp Charging:
http://www.prc68.com/I/BatChg.shtml#Burp

Have Fun,

Brooke Clarke
http://www.PRC68.com
http://www.end2partygovernment.com/2012Issues.html
http://www.prc68.com/I/DietNutrition.html

Robert Roehrig wrote:

There are some other failure modes for gel cell (and other lead acid types)
batteries.

One is a shorted cell caused be the plates warping and breaching the
separator insulation. This is not recoverable.

Another more likely failure is corrosion of the connections to the plates.
Also not recoverable.

If the battery is more than five years old it is most likely time to trade
it in for a new one.

Regards,
Tom

----- Original Message -----
From: "Charles Steinmetz" csteinmetz@yandex.com
To: "Discussion of precise time and frequency measurement"
time-nuts@febo.com
Sent: Sunday, July 27, 2014 3:41 PM
Subject: Re: [time-nuts] OT Gel Cell question

At 04:09 PM 7/27/2014, Tom Miller wrote:

I have used uninterruptable power supplies and standby power supplies for decades at work to keep mission-critical hardware online. I concur fully with Tom - depending upon the equipment they are used in and the quality of the original cells I replace gel cells every three to five years. It is much better to replace cells at a time of my choosing than to try to stretch their use and have them fail when needed.

Dale H. Cook, Contract Engineer, Roanoke/Lynchburg, VA
http://plymouthcolony.net/starcityeng/index.html

I too have spent a lot of time charging batteries using different methods on
various chemistries.  Once upon a time, I build a number of suitcase battery
chargers for the US Army that allowed them to charge every portable secondary
battery type that they had in inventory... SLA, AgO, NiCD, NIMH,
LiIon...  I proved a concept, and someone else got to make all of the money
off of it when the ARMY shopped my prototypes around... but I digress.

When you try to charge a sulfated lead acid cell, you can think of the cell
as being a bunch of little parallel lead acid microcells (uCell).  Each is in
some state of charge/discharge.

So imagine this:

+--+--+--+--+--+--+.....+--+---Plus terminal
S..S..S.[B].S..S..S.....S..S
+--+--+--+--+--+--+.....+--+---Minus terminal

In this case, all of the "S"s represent a microcell (uCell) that is highly
sulfated, and the "[B]" represents a microcell that is in perfect condition,
and is taking a charge normally.

If you try to put current into this lead acid cell, the sulfated uCells will
appear as open circuits (due to the sulfate's insulating properties), and the
good uCell will take all of the current, and will keep the voltage down to a
low enough value that the sulfated uCells will not see any significant
electrolysis action.

So you say, "Pooh, I want the sulfated uCells to charge too!" and up the
voltage across the lead acid cell, and poof!  The good uCell dies from over
heating, revealing a new uCell that wants to charge, and poof, it dies,
revealing another uCell that wants to take a charge, and poof...

You get into a situation where your success causes your failure.

If, instead, you apply high voltage pulses to the lead acid cell, you can
sometimes beat the system.  The good uCells will take a hit, but it is short
enough that they don't have time to burn up, and the sulfated uCells will
get to draw enough current during the pulse that a little electrolysis will
happen, and convert some of their sulfate back into oxide and acid...

Sometimes you can win by using a pulse charge system.

However, there is a little physical problem that has to be understood.  Part
of the way the lead acid batteries get their high current handling densities
is because the lead plates are made to have high surface area.  They are kind
of like sponges on the surface.  And, lead sulfate takes up significantly more
room than lead oxide.  Sorry, that is the way it just is.

So, when a cell gets all sulfated up, the lead sulfate that forms in the deep
nooks in the mossy lead electrodes fills the nook up so full that it breaks
it apart, and damages the cell plate.  This happens, albeit slowly, even when
you treat the battery nicely.

You can't win. Long term everything heads towards entropy.

-Chuck Harris

Brooke Clarke wrote:

it is not a high performance battery but extremely robust, see there
http://www.nickel-iron-battery.com/
it is no polluting, it could be shorted out overcharged
if you are lucky and find one old forklift with Edison Battery -- which
was built some fifty years ego....it will out last you too
you could charge in current mode, C/10, 2C nothing will happen just
replace evaporated water in the elctrtrolyt which is KOH
73
Alex

On 7/27/2014 2:41 PM, Chuck Harris wrote:

A minor nit

The self-discharge rate is pretty high (20 to 40% per month) and the
charging is not as efficient.

Power density is pretty bad too.

For forklift operation this is not a problem as weight is a good thing, they
are topped off every night and the power used to run a forklift is minimal
given the overall consumption of an average factory.

Wikipedia has a nice comparison

http://en.wikipedia.org/wiki/Nickel%E2%80%93iron_battery

http://en.wikipedia.org/wiki/Lead%E2%80%93acid_battery

Here is a vendor:

http://ironedison.com/

Dave

A small disagreement on a couple of points....

Lead sulfate does not dissolve (in the normal battery chemistry),
and does not go all over the place. It forms at the lead and the
lead oxide plates, during discharge, and there it stays
(unless it breaks off) until you charge the cell.  It is the
electrolytic cell action that allows the lead sulfate to be
converted back into lead metal, lead oxide, and sulfuric acid.

Everyone wishes lead sulfate could be dissolved safely, as this
could be a way of recovering batteries that have been overly
discharged.

Lots of snake oil remedies have been created that tout to do just
that... things like lime juice, ETDA, adding more sulfuric acid...
AFAIK, none of them really work.

Shorting in a wet (flooded) lead acid battery happens because the
charging/discharging action causes the creation and destruction of
lead sulfate, and because the lead sulfate is less dense than the
lead and lead oxide it replaces, it flexes the plates.  The flexing
causes some of the lead sulfate to break free of the plates, and
drop to the bottom of the cell.  Because energy density is
important in a lead acid battery, the manufacturer wastes as little
space in the battery case as possible by putting the plates as
close to the bottom of the battery "jar" as it dares.  This allows
the lead flakes to build up on the bottom until they reach the
level of the plates and short them out.

The gel cells, and glass mat cells short because the lead dendrites
that sometimes grow as a result of charging/discharging, pierce the
separator and short the plates directly.

-Chuck Harris

Neville Michie wrote:

To clear up the point,
lead sulphate is very much more soluble in water than sulphuric acid,
and when batteries get flat all the sulphuric acid is reacted leaving
only water. That is why no current will flow when trying to charge them.
It is all well documented, see:
Vinal.G.W. (1945) Storage Batteries,
John Wiley & Sons, Inc. New York Pp. 464

The sulphate is more soluble at higher temperature, and the daily thermal cycling
of an uncharged battery adds to the damage.

There are many popular myths and partial truths abroad, largely, I guess,
because the study of batteries is in few current engineering courses.
Magic additives to restore dead batteries have been around for 100 years,
but none of them are effective.
The only trick I have seen was an old guy who heated car batteries in an oven,
I never found out how long or how hot, he made a living reselling them
with a money back six months guarantee.
cheers,
Neville Michie

On 28/07/2014, at 1:59 PM, Chuck Harris wrote:

Neville,

Sorry, I don't agree.  There is plenty of ion exchange
capability in the "water" left over from a totally dead
lead acid battery to corrode the skin off of your hands.

I have never found one where the specific gravity of the
water reached 1.0.  Even a couple of drops of acid in
the water would be sufficient for significant current to
flow.

However, it still won't take any charge.  Not even a
milliamp at 15V.

The reason it won't charge is the lead sulfate covering the
lead plates is a very good insulator.

And, to quote my old college chemistry book:

• General Chemistry, 4th Edition, Nebergall, Schmidt and
  Holtzclaw, DC Heath and Company, 1972. p862:

"Lead sulfate PbSO4 is formed by ionic combinations, and
is insoluble in water but readily dissolved by solutions
containing an excess of alkali or acetate ions..."

I stand by my statements.

-Chuck Harris

Neville Michie wrote:

Ever use batteries to back up your time toys David?

I would bet they were lead acid.  More that a few
folks on this group are using lead acid to run such
things.  Discussions of charging, discharging, and
care of batteries is just as apropos, in my opinion,
as discussions on which coax to use, or which receiver
to use to run your GPSDO... Or for that matter which
SBC to use to run your favorite time hack.

It is all part of the infrastructure necessary to
make the study of fine time possible.

-Chuck Harris

David C. Partridge wrote:

That's for sure.  Lead Acid batteries run everything except where power
density is critical.
We all need to know as much as possible about them.  I thought that I knew a
lot, but the dialogue on this list has raised my understanding
significantly.

Thanks to all who have contributed so far.  A treasure trove of information.

Regards, John K1AE
 
Sent: Monday, July 28, 2014 8:39 AM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] OT Gel Cell question

Ever use batteries to back up your time toys David?

I would bet they were lead acid.  More that a few folks on this group are
using lead acid to run such things.  Discussions of charging, discharging,
and care of batteries is just as apropos, in my opinion, as discussions on
which coax to use, or which receiver to use to run your GPSDO... Or for that
matter which SBC to use to run your favorite time hack.

It is all part of the infrastructure necessary to make the study of fine
time possible.

-Chuck Harris

David C. Partridge wrote:

On 7/28/2014 1:12 AM, David C. Partridge wrote:

I worked on cesium standards (5071A)
at HP/Agilent with Len Cutler of flying clock
fame.  You better believe that batteries are
time related.  We jumped through all sorts of
hoops to get the 5071A power consumption down
to a few dozen watts so it could run off of
batteries.  The other reason for minimizing
power consumption was to avoid fans.  HP also
used to sell auxiliary battery systems in
case the user needed more battery run time
than the internal battery was capable of.

Rick Karlquist N6RK