shorted (?) lead-acid battery

[aurgathor]

Yesterday I started to charge a car battery that was sitting unused
for quite a while with a 1A charger. (my other one is broke)
Initially, the battery was around 6V, that jumped to over
15 when I connected the charger, but dropped in about 30
seconds to around 10V after the oxide layer broke down.
A couple of hour later I measured the battery, and it was around
10.40V, low enough that I was wondering if it had a shorted cell.
Then I measured it again before going to bed -- 8.50V!!.
This morning -- 6.50V, and the charger was too hot to touch,
and I disconnected the charger at this point.

I've never seen anything like this. I figured since the charger can
supply so little current (was 850 mA @ 8.5V) there's no way it
can overcharge or damage a car battery. I know something isn't
right since after a day, even with a wimpy charger like that it should
read more than 6.5V. Any idea what's happening? How did the
cells become shorted, if that's the case? (the battery wasn't moved
or jarred since charging began)

TIA

 

[Dave Platt]

Yesterday I started to charge a car battery that was sitting unused
for quite a while with a 1A charger. (my other one is broke)
Initially, the battery was around 6V, that jumped to over
15 when I connected the charger, but dropped in about 30
seconds to around 10V after the oxide layer broke down.
A couple of hour later I measured the battery, and it was around
10.40V, low enough that I was wondering if it had a shorted cell.
Then I measured it again before going to bed -- 8.50V!!.
This morning -- 6.50V, and the charger was too hot to touch,
and I disconnected the charger at this point.

I've never seen anything like this. I figured since the charger can
supply so little current (was 850 mA @ 8.5V) there's no way it
can overcharge or damage a car battery. I know something isn't
right since after a day, even with a wimpy charger like that it should
read more than 6.5V. Any idea what's happening? How did the
cells become shorted, if that's the case? (the battery wasn't moved
or jarred since charging began)

From what I've read of lead-acid battery design, my understanding is
that one not-uncommon failure mode is that deep discharging (whether
due to excessive load or due to failure-to-keep-charged-while-in-
storage) can result in a physical deterioration of the plates in each
cell. The plates weaken, disintegrate, and the rubble falls
to the bottom of the cell. You can end up with chunks of the plate
material forming bridges across/around/through whatever is normally
used to keep the plates separated, and this shorts out the individual
cells.

If this is what happened to yours, then the charger wasn't at fault.
The battery was fatally rotted even before you hooked up the charger,
and the electrochemical changes which occurred during the charging
process (and perhaps converted the rubble back to a conductive form)
simply made the existing damage apparent.

As far as I know there's no practical way to recover from this... take
the battery to a dealer for recycling, buy a new one, and treat the
new one a bit more gently

--
Dave Platt <dplatt@radagast.org> AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

 

[aurgathor]

"Kim Clay" <kimclay@myrealbox.com> wrote in message
news:c4jjv0hc94hi6mamo3ui5pomt1qr85s298@4ax.com...

On Thu, 27 Jan 2005 11:41:56 -0800, "aurgathor" <spam-me@if-you.com
wrote:

Yesterday I started to charge a car battery that was sitting unused
for quite a while with a 1A charger. (my other one is broke)
Initially, the battery was around 6V,
Three discharged (but not completely) cells = 6V, the other three cells
are at 0.0V each due to internal shorts.

That is not correct. A discharged battery can go down that much,
or even more without the cells having internal shorts. Case in point,
a couple daysbefore this one I had a battery that measured 1.7V!
(in car, with a light left ON). In a couple of days, that battery was
measuring 14V, and worked just fine. I just checked it today --
12.85V.

Based on the voltage measurements after a few hours of charging
(10.40V -> 8.40V -> 6.40V) some cells must've become shorted
during the charging process. Alas, I no longer remember the voltage
after the first 10 - 15 mins of charging -- that may have been close to 12V.

Because (from your first sentence) "battery that was sitting unused
for quite a while". Car batteries self discharge just sitting on the
shelf. A discharged battery that sits is quickly self destructing
internally, as you have found out.

I expected sulfation, and while that's no good either, it's less
deadly, and it's easier to reverse than an internal short.

I guess material fell from the plates, created a highly conductive
sludge in the bottom, and that's what shorted the cells out.

One of my friend got a 100A or so charger, so I wonder if
I can blow the shorts with that. ;-) Of course, I'd need to
find a good enough container first incase the whole battery
blows.

 

[Art]

"Good Container" ?? Ever see one of these batteries blow up tossing
residue, poison, acid, etc all over the place when someone attempts to apply
a high charge rate to "Blow Off the slight shorts"??
Not a nice sight exp when it comes in contact with someone's face or
exposed skin. Not a right pleasant experience in the least. Personally know
at least one person who lost one eye and has facial burns as a result of
trying to do what others are implying may work. Buy a NEW BATTERY!
"Kim Clay" <kimclay@myrealbox.com> wrote in message
news:4tvlv0h5r66qn128gj8lieuqm71fp8dsan@4ax.com...

On Fri, 28 Jan 2005 18:01:54 -0800, "aurgathor" <spam-me@if-you.com
wrote:


"Kim Clay" <kimclay@myrealbox.com> wrote in message
news:c4jjv0hc94hi6mamo3ui5pomt1qr85s298@4ax.com...
On Thu, 27 Jan 2005 11:41:56 -0800, "aurgathor" <spam-me@if-you.com
wrote:

Yesterday I started to charge a car battery that was sitting unused
for quite a while with a 1A charger. (my other one is broke)
Initially, the battery was around 6V,
Three discharged (but not completely) cells = 6V, the other three cells
are at 0.0V each due to internal shorts.

That is not correct.
It is correct! Your original question was about a car battery that had
been "sitting unused for quite a while" which you measured at "around
6V".

A discharged battery can go down that much,
or even more without the cells having internal shorts.
Yes, one can deeply discharge a "good" battery down to 0.0V & after
the load is removed the cells _may_ recover. A new battery discharged
accidently to 0.0V & promptly recharged will probably be OK. A old
battery discharged in the same way may not make it.
The one key point is that the battery is not left in the discharged
state for long. Once the load is removed the cells start to recover. A
non-defective battery will bounce back (even without any charging
applied) to around 11-12V within 24 hours & probably less. I have never
timed it

Case in point,
a couple daysbefore this one I had a battery that measured 1.7V!
(in car, with a light left ON). In a couple of days, that battery was
measuring 14V, and worked just fine. I just checked it today --
12.85V.
Ran the battery down & it got promptly recharged.

Based on the voltage measurements after a few hours of charging
(10.40V -> 8.40V -> 6.40V) some cells must've become shorted
during the charging process.
The cells were shorted from the beginning. These are not 0.0 ohm
internal shorts but some higher resistance that have bridged the plates.
It seems your ~1A charger was enough to overcome the internal cell
short (or bridging resistance) of two of the cells but not the third.
This resulted in the 10.40V reading early in the charging process.
During the rest of the charging process the internal shorts within the
other two cells slowly decreased in value resulting in your 8.4V reading
& the ending 6.4V.

Alas, I no longer remember the voltage
after the first 10 - 15 mins of charging -- that may have been close to
12V.
Indeed it may have been "close to 12V" near the start. If the charger
can overcome the internal short a cell will attempt to recharge. The
plates just fell apart & created a harder short. It took a while for all
three cells to end up the same way - hard short internally.

Because (from your first sentence) "battery that was sitting unused
for quite a while". Car batteries self discharge just sitting on the
shelf. A discharged battery that sits is quickly self destructing
internally, as you have found out.

I expected sulfation, and while that's no good either, it's less
deadly, and it's easier to reverse than an internal short.
If you have a lead acid (12V) battery that is at ~10.5V or better it
has a chance of becoming useful no matter how long it has set. If it is
10.5V it may (probably) have a shorted cell. These are measurements
taken of an unknown battery that has been sitting for >24 hours.

I guess material fell from the plates, created a highly conductive
sludge in the bottom, and that's what shorted the cells out.
You were attempting to recharge a battery in which 3 cells already had
internal shorts (or the battery would have been closer to 12V to start
with). These cells had been in this condition for an unknown length of
time. The shorts just became more solid as the charging progressed.

One of my friend got a 100A or so charger, so I wonder if
I can blow the shorts with that. ;-) Of course, I'd need to
find a good enough container first incase the whole battery
blows.

Even if you could magically make the shorts disappear the basic
trouble is still there. The cells are falling apart internally.

Kim