alec(at)alecmyers.com
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 Posted: Sat Feb 03, 2024 7:59 am Post subject: One for the battery gurus: recovery from deep discharge |
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Here’s how it turned out: 12 hours on a bench PSU at 14.4v, then 12 hours rest, then I attached a different “smart” charger that showed the battery as discharged, but did proceed to engage the charging cycle. 24 hours after that, the charger was showing the battery at 100% charge and it had enough juice to start the engine, and I flew for about an hour.
Hopefully it will maintain enough energy to power a start cycle again, some time next week.
Thanks for the comments, Bob!
On Jan 31, 2024, at 22:31, Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com> wrote:
At 04:09 PM 1/30/2024, you wrote:
| Quote: | --> AeroElectric-List message posted by: Alec Myers <alec(at)alecmyers.com>
I have an SBS-J16 battery in an aircraft in which the battery master was left on for two weeks (I know).
When found, the open circuit terminal voltage had dropped to 2.2 volts. A Dewalt sophisticated battery charger didnât want to have anything to do with it, |
Yeah . . . many smart chargers do a pre-assessment of the target
battery and will not take on the task unless the terminal voltage
is above some minimum level . . . I have a couple chargers that
do this.
A temporary parallel connection of the smart-charger and some
other voltage source, like another battery will often convince
the charger that it's time to go to work.
Now, recall the days long before RG/GlasMat batteries.
The 'wet' stuff inside was (and still is) a dilute mixture
of water and sulfuric acid. Pure water is a very poor
conductor of electrons . . . but adding some
combination of free ions like salt, sodium bicarbonate,
or sulfuric acid to the water and it becomes a ready
conductor of current.
Recall that we could test the relative state of
charge for a lead-acid battery by measuring the
electrolyte's DENSITY with a hydrometer. The
legacy float/in/glass hydrometer is generally
calibrated in density vs. state of charge
where electrolyte 12% greater than 1.000
(pure water) is zero-percent; 26% is full
charge.
Note in attached figure (shamelessly stollen
off BatteryUniversity.com), 0% state of charge
on a 12 volt produces an open circuit reading
on the order of 11.9 volts.
You cited an open circuit voltage of 2.2 volts . . .
Hmmmm . . . less than 0% state of charge?
Actually, yes. Active material in the plates
had sucked still more acid from the electrolyte
than what would produce any useful energy
from the chemistry.
The closer to pure water . . . the more depressed
conductivity. Hence, first attempts to push energy
back into the battery will be met with lots of
resistance . . . no pun intended.
I recall reading a qualification test on
a Concorde battery document where a fully
discharged battery is dead-shorted for a
period of time after which a recharge
protocol calls for applying a higher than
normal voltage until significant recharge
current is observed. The test proceeds with
a normal constant voltage/constant current
charge. After top-off, the battery is cap-checked
and must demonstrate some minimum.
I dug around in the library but could not
come up with that document so I cannot quote
exact times and values. But note that this
is a quality test for a new battery. While
a certain level of degradation is expected,
the battery is EXPECTED to recover by some
minimum amount required for return to
service.
| Quote: | | so Iâve now put it on charge with my bench power supply at 14.4V limited to 4 amps. Initially the battery resistance was very high, and increasing - the voltage was limited at 14.4V and the current dropped from 1.3 amps, to about 1.1 amps, within a couple of minutes, and then started to ramp up, about 1mA per second. After being on charge for an hour or so, the current it is accepting has risen so the current limiting has kicked in, presently at 4 amps and the terminal voltage has dropped to 14.3 V. |
Yup, this is expected and you may well
recover this battery to some level for
continued service. After a 24-hour float
at 14.4, let it see idle for 24-hours
then do a cap check followed by recharge
and a load test.
| Quote: | | Iâm curious why the resistance was so high to start with, why it has now dropped (to what seems ânormalâ charging behaviour to me) and also to know if this battery has a chance of resurrection,. Itâs only a couple of years old, so if it will soldier on after its mistreatment, I would be happy. What are my chances, do you think? |
As Lord Kelvin oft admonished, if you
don't know the numbers, what you DO know
is of limited value.
Bob . . .
////
(o o)
===========o00o=(_)=o00o=========
< Go ahead, make my day . . . >
< show me where I'm wrong. >
=================================
In the interest of creative evolution
of the-best-we-know-how-to-do based
on physics and good practice.
<Gravity vs StateOfCharge.jpg>
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