doa agm again

  What exactly happens inside an AGM if it is allowed to go dead?

 George, I do understand where you are coming from in your posts but there
are exceptions to everything but I do not want to beat a dead horse.

 I know how normal wet type batteries work and I have a good idea about how
AGM's are made.

 From what I understand, the plates in an AGM build up sulpher on them if
left in a low voltage state. (correct me if I am wrong here)

 What has got me confused is the battery reads 12.6 to 12.8 volts after
sitting for 12 hours but has very little capacity.

Note: I have not done a capacity check on this battery for 3 weeks. It has
been charged with 6 watts for 2 weeks and 3 watts for 1 week so far about
6-8 hours a day.

 This is just an experiment....I do not expect the battery to be able to
produce more than 50% capacity (wishful thinking) but if I can bring it up
some, I may be able to use it for some led yard lighting. OK it has 2 leds
running off it 24/7 now but I would like to be able to run 50 off of it
(more wishful thinking but not impossible)

 I can try pulse charging it, maybe some RF ( I could hit it with 100 watts
of RF on about any frequency from 1.8 to 30 mhz or 65 watts anywhere in the
2 meter band for very short periods of time but am not sure what that would
do and most likely unsafe to do so.I could also pump any voltage into it up
to 15 volts from 2 to 6 amps.(hell I could hit it with a welder and might
just do that to watch it blow up from across the street LOL....)jk

 Like I said this is an experiment. I am just looking for ideas from people
that know more than I do about AGM,s ( which is most everyone here)

 For the test, lets assume that the battery was not overcharged (in that
case I would have given up long ago) but just allowed to discharge to 10
volts and sat at that state for a while (the 10 volts is just a number I
pulled out of the air, not a complete discharge but a bad one)

Like I said this is only an experiment and I will do a load test on the
battery this weekend to see if my efforts so far have done anything..

 thanks joe

  Merlin-7 KI4ILB wrote:

Lead acid batteries will sulphate if allowed to sit in a low state of
charge for lengthy periods. AGMs are lead acid batteries, as are gell cells.


Yes, I have a battery here that is waiting to go for scrap that has a
capacity of around 9 hours. It is supposed to be a 200 Ah battery.

Batteries are not, as some people believe, a box full of electricity.
Batteries are a box of chemicals, which have the potential to produce
electric current under the correct conditions.

AGMs are a sealed lead acid battery. If the chemicals, in this case
oxygen and hydrogen, are allowed to escape then the capacity of the
battery is reduced.


I think you are flogging a dead horse, but just maybe it will get up and
run. Just don't hold your breath.


The experiment has been done many times, by many people. Negative
results are the norm.


As long as you're having fun.

--
Posted via a free Usenet account from http://www.teranews.com

 Joe,

Here's the information that I've been using for mine. It's from an
bunch of different articles that I've found.

They may not go dead very easily, but if they do, you have to have the
capability of "equalizing" them to get them back. When AGM's go dead,
they will charge back up under normal charge parameters just like they
normally do, slightly faster maybe, but they will not hold that charge.
I.E., their true capacity will be greatly diminished. If you find that
the batteries reach 13.1 volts and yet as soon as a load is put on them
they start dropping down much faster than normal you need equalization.
Oh, yes, equalizing a sealed battery is not a good thing to do, but
Lifeline will heartilly recommend it as soon as they hear what you have
to say the problem is.

 15.5V for 3 hours is an AGM's equalization parameter. If you have a
newer Link 2000 with an AGM battery selection (#3), then it "may" have
this parameter in it. Some do, some don't. If not, set it for Lead Acid
(#1) and raise the ambient temp to max... 120? and let it run for 3
hours. That will do 15.75V which is ok. This is of course, AFTER you
have charged them normally and they "show" full charge.

Instead of using electrolyte sloshing around the case as a free liquid,
in AGM batteries the electrolyte is "absorbed" and held within a
fine mesh of fiberglass cloth or mat in
what's referred to as a "starved" state.This starved state means
the cloth is nearly - between 90 and 95 percent- but not fully,
saturated; a small portion remains gas-
rather than liquid-filled.This gas void allows for the transfer of
oxygen from the positive to negative plate in its molecular form during
charging, which suppresses the
production of hydrogen.Water is produced and remains within the
battery.The entire recombinant process occurs within the battery's
sealed chamber,under slight pressure.
Thus, AGM batteries never require the addition of water, making them
maintenance free.

Additionally,the glass mat material is compressed as it's packed into
each battery cell,making for an exceptionally sturdy,
vibration-resistant design (the U.S. Navy thinks so; they use AGM
batteries in combat aircraft).This high-density packing and other
unique cell features give the AGM battery particularly low internal
resistance, resulting in
what is one of the AGM's greatest attributes - an exceptionally
fast recharge time.They will accept the highest charge rate of any of
the three popular marine battery
chemistries. Additionally, this low resistance means AGM batteries
maintain a higher terminal voltage under heavy loads such as those
imparted by inverters, windlasses,
starters and bow thrusters.The low resistance also means AGM batteries
tend to stay cooler during heavy charging and discharging applications.

Perhaps the greatest shortcoming of AGM batteries -is their
sensitivity to chronic under- and overcharging,particularly in the
float mode. The requirements vary from
manufacturer to manufacturer. For example, Concorde Battery Corp.,
manufacturer of a complete line of AGM batteries,calls for 14.1 to 14.4
volts for bulk charging and
13.1 to 13.3 volts for float charging, at 77º F (25º C). East Penn
Manufacturing, another maker of AGM batteries specifies a maximum
charge voltage of 14.6 volts and a
float of between 13.4 and 13.7 volts,again at 77º F.Thus, not only are
the charge voltages
different from conventional flooded batteries, they vary from
manufacturer to
manufacturer. Conventional flooded batteries call for a bulk-charge
voltage of about 14.2 and float of 13.2,once again at 77º F.Not a huge
difference,but an important one, particularly where multistage
high-current chargers are used. It's important to note that while
AGMs will suffer from chronic under- or overcharging, so too will all
lead-acid batteries.

The importance of using a fully regulated multistage
temperature-compensated charger for AGM batteries cannot be
overemphasized. Ferro-resonant (old-fashioned and unsophisticated)
powered chargers or internally regulated automotive alternator
regulators are inadequate for charging these and most other deep-cycle
batteries. These basic, single-step chargers offer a constant voltage
rather than what's needed - a voltage-regulating or
voltage-limiting charge profile. Because of the recombinant technology
used in AGMs, they are entirely intolerant of venting.That is,if
seriously
overcharged, their regulating valves will open to prevent
over-pressurization of the case,resulting in a permanent loss of
hydrogen and oxygen or water. If allowed to continue, this process,
tantamount to never adding water to a conventional flooded cell, will
eventually destroy the battery.

Temperature compensation important

Where AGMs are concerned, temperature compensation factor is especially
important. It
ensures a full charge at the highest rate possible, which equates to
the shortest charge time,while preventing damaging overcharging. Even
if the battery isn't driven to the
venting stage,constant,chronic overcharging caused by a lack or failure
of temperature compensation in the charge cycle will lead to galvanic
corrosion of the positive grid
and shedding of the active plate material, which is essentially the
muscle within every battery.The structure that supports the lead in the
positive plates will simply corrode and crumble.

In the case of AGMs using envelope-type separators, this material will
be retained within the envelope;however, its effectiveness is
considerably diminished. The full enclosure of the positive plate
within one of these electrolyte-permeable envelopes is a decided
advantage for batteries of any chemistry.This shed material,if allowed
to accumulate at the bottom of a battery cell,will eventually lead to
shorting between the plates, a condition that results in the
battery's ultimate demise.

 
Well, it's lead sulfide, which is called sulfation, but the idea is
essentially correct.  The plate material gets converted to something
that doesn't work as a battery any more, and capacity drops.


Exactly the symptom.  [This symptom could also be the result of
overcharging the battery for long periods of time over it's
recombinant rate, which has dried out the battery, in which case it's
trash, but that doesn't sound like what you've done.]

In my experience, these batteries can be recovered by use of a
constant current charge at something below the recombinant rate of the
battery with no voltage limit (I've put 18 volts across a single 2V
Gates cell) for a long period of time (a month).  You may notice the
voltage _rise_ and then _fall_ as the sulfate is converted back to
lead (oxides), and then normal charging will occur.

The recombinant rate is that charge rate where the battery can
recombine hydrogen and oxygen to water without venting.  If you
continue to charge a fully-charged battery past that rate, you'll vent
excess pressure, and lose water, eventually drying out the cell. Gates
Cyclon recombinant rate is about C/500, so charging at that rate will
take on the order of three weeks, plus the time needed to convert the
sulfate.

Also note this is a constant current charge, with no voltage limit,
not a normal battery charger.  I use a lab supply or a high-voltage
box I built with appropriate dropping resistors.

 

What about using 2-3.2 watt panels with an open circuit of 22 volts into the
100ah AGM for say 6 hours a day wired directly to the battery?
 Ok really I think the panels may put out 5 watts together in real world
conditions and I do not think that 5 watts could overcharge the battery at
any voltage. Does this sound ok to you?
 Remember it is just an experiment but I dont want to cook it ...

 Joe