charging a fully discharged car lead acid battery

[Asimov]

"Jim Adney" bravely wrote to "All" (12 Oct 05 21:16:45)
--- on the heady topic of "Re: charging a fully discharged car lead acid battery"

JA> From: Jim Adney <[email protected]>
JA> Xref: core-easynews sci.electronics.repair:345101

JA> Any charging current, up to the point where you get 14.2 V across the
JA> battery terminals will be fine. (Above 14.2V, you start to dissociate
JA> water into hydrogen and oxygen. If this happens vigorously, it can
JA> damage the porous sintered plates, plus you get an explosive gas.)


Jim,

I always thought a little bubbling near the end of charge might be
desirable because it physically sheds some sulfation off the plates
and leaving them with more active area. The battery must be monitored
more often near end charge for this to happen safely, though.

A*s*i*m*o*v

.... I worked hard to attach the electrodes to it.

 

[Veggie]

A discharged, but not dead, battery is ok to jump start and allow the
alternator to charge it up. A discharged battery will read around
11-12 volts unloaded or minimal load, 100mA. 8 volts on the battery
indicated that it was in a deep discharge state, not good.

After a couple of days (daytime only) at 1 amp charge, it is now reading
12 volts no load. Interesting that no matter where I dial in the
current, it stays at 12.0 volts. The battery is acting like a voltage
regulator of sorts.

Unless it was a nearly new battery, I would do one of two things if
it does charge and start the car: 1. Get it load tested on the
coldest day in the near future, replace if it is marginal. 2. Simply
replace the battery with a new one for the peace of mind.

It's just under two years old, original factory battery. When I topped
it off with distilled water, tops of the plates looked great. Looked
just like new finned aluminum heatsinks, clean and no gunk. There was
some oil slicks on the electrolyte, no doubt from the red bearing grease
someone (the factory?) had smeared all over the terminals. There was
semi liquid red grease underneath the caps too.

Isn't there a better choice for corrosion protection than regular petro
grease? In the 80's, I remember a cream colored paste for that purpose.

 

[Dave Plowman (News)]

I've heard that the reason a totally flat battery won't charge is that
its chemistry has changed because of sulphation. To get it to take a
charge, a much higher voltage is required, which your alternator may not
be able to deliver. Perhaps your trickle charger has a sufficiently
high open-circuit voltage to overcome the problem. After the trickle
current had flowed for a sufficient amount of time, the chemistry
returned to normal.

Well, yes. Think I've said that. Many times. ;-)

But this won't *damage* the car alternator. It simply won't charge the
battery.

 

[Dave Plowman (News)]

After a couple of days (daytime only) at 1 amp charge, it is now reading
12 volts no load. Interesting that no matter where I dial in the
current, it stays at 12.0 volts. The battery is acting like a voltage
regulator of sorts.

Think you said the maximum voltage of the bench supply was 12 volts. You
can set the 'current' to whatever you like, but without the required
voltage the battery won't get fully charged. You need near 14 volts to do
this.

 

[[email protected]]

Some auto repair experts and manufactures state that trying to charge a
fully discharged car battery with an alternator can damage it. (note:
it does not say WILL damage it but CAN damage it)

Boschusa.com:
Q. Can I use my alternator to recharge a discharged battery?
A. No! When installing an alternator, the battery should be fully
recharged before vehicle use. In many cases, depending upon how
thoroughly discharged the battery is, it can take 4-8 hours. Most
technicians and DIYers don't want to wait that long so they just get
the vehicle running, and figure that by driving the car around the
alternator will charge the battery. In some cases with weather extremes
the battery never gets fully charged, and in all cases the alternator
is being overly stressed asking it to do a job it was not designed to
do. This leads to premature failure.

popularmechanics.com:
Use a battery charger until the open-circuit voltage is 12.6 volts.
Avoid quick-charging, as the high current can warp the plates. If the
battery is deeply discharged, don't use the engine's alternator to
charge it by jump-starting and running the vehicle--the alternator is
not designed to produce that amount of current for that long and may be
damaged.

Given the high cost to replace an alternator and the not so do-it
yourself friendly of replacing one on a front wheel drive car, it would
be better when possible to go on the side of caution. The problem
arises in not knowing which vehicle charging systems can or cannot
handle running at the higher current, or which ones limit the current
to levels that will not possibly cause damage.

 

[Veggie]

Think you said the maximum voltage of the bench supply was 12 volts. You
can set the 'current' to whatever you like, but without the required
voltage the battery won't get fully charged. You need near 14 volts to do
this.

I was wrong about the supply. It is 12 volts nominal, but it adjusts up
to 14.0 volts. It is not a variable current supply, it is a variable
voltage supply.

 

[René]

Says nothing about damaging the alternator, though.

It's true an alternator won't charge a *totally* flat battery. I had this
once after leaving the car at an airport long stay carpark while on
holiday. Still don't know what caused it. Got a jump start and drove the
50 or so miles home. At the end of the journey the battery was still
*totally* dead. Put it on trickle charge for a week using an ancient non
regulated charger. After it was fully charged I checked the capacity by
discharging into a load and timing it. Only a rough test. And it would
start the car ok. Dunno if this shortened the life as it was not new and
I'd bought a replacement. ;-)

Without having followed the whole thread - I am somewhat confused!

You drove a car 50 miles with a flat battery? Either the battery has a
low internal resistance (as it should have), and the depleted battery
would keep the actual system voltage low. The car would not run (car
management / ignition does not operate)

-or the internal resistance is very high (battery totally ruined), in
which case the alternator is not "buffered" and voltage spikes way
above 30V may occur. This usually blows all sensitive electronics.

(thus the advise never to unhook a battery in a running car)

Possibly the battery was not flat at all, just not powerfull enough
for a start? (radio would work, as would lights?)

I take it the car in this case is an diesel powered oldtimer?
A damned robust car anyway!

 

[Dave Plowman (News)]

Use a battery charger until the open-circuit voltage is 12.6 volts.
Avoid quick-charging, as the high current can warp the plates. If the
battery is deeply discharged, don't use the engine's alternator to
charge it by jump-starting and running the vehicle--the alternator is
not designed to produce that amount of current for that long and may be
damaged.

I must avoid long journeys with headlights ablaze, wipers going, heated
rear window on heated seats, high powered stereo blaring, etc etc etc.
Perhaps that's why my alternator is water cooled?

 

[Dave Plowman (News)]

Without having followed the whole thread - I am somewhat confused!

You drove a car 50 miles with a flat battery? Either the battery has a
low internal resistance (as it should have), and the depleted battery
would keep the actual system voltage low. The car would not run (car
management / ignition does not operate)

With a heavily discharged battery, the regulator in the alternator acts to
keep the voltage at a maximum of about 14 volts. And although the internal
resistance of a battery does change with state, it's always extremely low
unless knackered. Otherwise it would not be capable of delivering the
several hundred amps needed to start an engine.

-or the internal resistance is very high (battery totally ruined), in
which case the alternator is not "buffered" and voltage spikes way
above 30V may occur. This usually blows all sensitive electronics.

Only engine electronics on that car was the ignition unit. It had a radio,
etc.

(thus the advise never to unhook a battery in a running car)

Possibly the battery was not flat at all, just not powerfull enough
for a start? (radio would work, as would lights?)

Totally flat when I got to the car. Not even a glimmer from interior
lights or engine warning ones etc at switch on. Even the clock had stopped.

I take it the car in this case is an diesel powered oldtimer?

No - carburettor V-8

A damned robust car anyway!

A '74 Rover 3500S. Great fun.

 

[none]

I have a car with a battery that is completely discharged (accessory
left on for over 24 hours). Read 0 volts.

What is the best way to remedy this?

a) jump start - it seems to not be a good option as it dumps high
current into the dead battery. If you're on the road somewhere, sure,
you need to get going but jump starting seems to be undesirable.

b) put it on a battery charger, one of those 5/10/25 amp ones. If so,
which rate is the best for a completely flat battery?

There seems to be a lot said about sulfate build up on batteries. It
seems to be an unsettled subject on the Net, as many say one thing but
an equal number refute it. One claim in interesting to me- that leaving
a lead acid battery in flat condition for a long time caused sulfate
build up. Is this true, and what is a "long time"? Are we talking
days, weeks, or months?

Charge it using a charger, rate isn't that important unless you do
have alot of sulfation. Then you need to use a really high amp
charger, 40amp or higher, to burn off that sulfation.
You could have it tested at a decent battery shop for sulfation
levels.(and any possible shorted or dead cells as well.)
They'd have a charger designed for reviving problematic batteries as
well.
Jumping it off from flat dead is a no-no, especially with later model
cars with loads of electronics and mainly an electronic altenator.(
You can really do a number on the electronic regulator internalized in
most late model altenators. Burnt diodes, fried control chip etc...
trying to jump start and run with the battery that low.)
Better to remove the battery and get it charged up before running the
electronics off it.
One big reason to go with "old school" auto's if possible, less to go
wrong and rock solid reliability.( a heavy duty marine grade altenator
with a competitive ignition coil and double duty external voltage
regulator. If it's a stick you can just give it a push and you're off
and running.)

 

[Jim Adney]

I always thought a little bubbling near the end of charge might be
desirable because it physically sheds some sulfation off the plates
and leaving them with more active area. The battery must be monitored
more often near end charge for this to happen safely, though.

I get the impression that this is "common knowledge" but I think I can
persuade you that it's counterproductive.

The battery works by taking sulfate ions in and out of solution:
sulfuric acid goes to lead sulfate, etc. Lead sulfate which is shed
off the plates will fall to the bottom of the case and stay there as
an insoluble precipitate. In this process, it removes sulfate ions
from the process. It also removes lead from the plates.

The buildup of this precipitate may eventually short out the cell,
plus the permanent loss of sulfate ions weakens the sulfuric acid and
weakens the battery. The loss of lead may eventually lead to
degradation of the plate.

If you take your time and reverse the sulfation process slowly, you
won't have any of these problems.

How'd I do? Are you convinced?

In my opinion, there is really only one real stumbling block with
reversing sulfation and that is time. If you have time, it can be
fixed. If you don't, you'll just have to replace the battery.

-

 

[Jim Adney]

Sorry for the dumb question, but how many cells are in a 12 volt car
battery? Must be six at around 2 volts each. If this is right, then
your advice is to set the charge voltage at 14.1 volts. If I recall
right, the car's charging system runs at 13.8 volts so the 14.1 is right
in that ballpark.

Right, it's six. Charging systems run at 14.1-14.4V. I'm guessing that
the old 13.8V "standard" was actually what you could depend on at the
load end. I gather that modern batteries use a slightly different
chemistry (something about a bit of calcium added to the lead in the
plates) which makes them able to tolerate slightly higher voltages
without hydrolysis. I'm not really clear on this.

There is all manner of hubbub about pulsed desulfators, etc. For the
average person, taking a week or two with off the shelf equipment is
much desired over special desulfators.

I agree completely. If you have time this is not at all difficult.

Keep in mind that for most applications, you don't have to completely
reverse the sulphation, all you have to do is get the battery back to
a state where it can be put back in service. Once back in service,
normal usage will continue the restoration process.

-

 

[Jim Adney]

After a couple of days (daytime only) at 1 amp charge, it is now reading
12 volts no load. Interesting that no matter where I dial in the
current, it stays at 12.0 volts. The battery is acting like a voltage
regulator of sorts.

Yes, it's just like a big capacitor which you're slowly charging up.

There is one thing that you should check occasionally, and that is to
verify that you don't have a shorted cell in there, which would make
this a 10V (or 8V) battery. To test for this, just leave it off the
charger overnight and check the open circuit voltage in the morning.
It should be above 12V.

I know you did this earlier, and at that time it was still only up to
11 volts. At that time it looked like this was reasonable, but by now,
I think you should be back up to "normal." Haven't you put ~50 Amp-hrs
into this thing so far?

If the voltage drops to ~10V, then you have a shorted cell, and I
really don't think that is ever repairable.

I'm surprised that you're not higher in voltage by now, so maybe some
caution is worthwhile. Your 1 A charging is still fine; that won't
hurt anything.

But wait! Isn't your charger a 12V CC/CV lab supply? In that case, I
think you just need to switch to something higher in voltage. Just
keep the voltage under 14.1 V.

It's just under two years old, original factory battery. When I topped
it off with distilled water, tops of the plates looked great. Looked
just like new finned aluminum heatsinks, clean and no gunk. There was
some oil slicks on the electrolyte, no doubt from the red bearing grease
someone (the factory?) had smeared all over the terminals. There was
semi liquid red grease underneath the caps too.

The + and - plates will be grey and brown once it is fully charged.
When it is discharged, they will both be grey. Don't be fooled by the
paper separator in there. You'll know you're done with the reversal of
the discharged state when half of the plates have turned brown.

The color change won't occur uniformly. First you'll see brown peaking
out from under the grey, they just grey flakes on the brown, then all
brown.

Isn't there a better choice for corrosion protection than regular petro
grease?

Wish I knew. ;-)

-

 

[Veggie]

There is one thing that you should check occasionally, and that is to
verify that you don't have a shorted cell in there, which would make
this a 10V (or 8V) battery. To test for this, just leave it off the
charger overnight and check the open circuit voltage in the morning.
It should be above 12V.

I always disconnect it for overnight. It has been reading 12.0 volts
the last two mornings.

I know you did this earlier, and at that time it was still only up to
11 volts. At that time it looked like this was reasonable, but by now,
I think you should be back up to "normal." Haven't you put ~50 Amp-hrs
into this thing so far?

Well, it's more like 32 amp hours. The built in hygrometer is starting
to show green, so it is progressing. I can wait it out, no problem

If the voltage drops to ~10V, then you have a shorted cell, and I
really don't think that is ever repairable.

I'm surprised that you're not higher in voltage by now, so maybe some
caution is worthwhile. Your 1 A charging is still fine; that won't
hurt anything.

But wait! Isn't your charger a 12V CC/CV lab supply? In that case, I
think you just need to switch to something higher in voltage. Just
keep the voltage under 14.1 V.

I was wrong about the supply. It is 12 volts nominal, but you can dial
it up higher. To push 1 amp into it, the open circuit voltage is 14.
But when loaded onto the battery, it is rock solid at 12.0 volts.

 

[Jim Adney]

I always disconnect it for overnight. It has been reading 12.0 volts
the last two mornings.

Okay, good. This looks just fine and "normal" so far.

Well, it's more like 32 amp hours. The built in hygrometer is starting
to show green, so it is progressing. I can wait it out, no problem

Okay, completely normal progress. Exactly what you want to see.

I was wrong about the supply. It is 12 volts nominal, but you can dial
it up higher. To push 1 amp into it, the open circuit voltage is 14.
But when loaded onto the battery, it is rock solid at 12.0 volts.

That's just the battery loading it down. Also perfectly normal for a
current limiting supply.

Whatever you did to this battery didn't seem to hurt it, but you
REALLY pulled it down flat. That's actually pretty hard to do, but
you're doing exactly the right thing to recover it.

At this point, I don't think you could do any harm by just leaving it
connected 24/7. You're only putting 12 Watts into it, with the
potential of going up to 14 Watts. That's not enough power to do any
harm under any circumstances.

-

 

[Veggie]

All done, recharge was successful. It was on a slow 1 amp charge for 7
days. On the last day, it seemed to be completely charged. I could not
push any more current into it. Raising the voltage merely caused
bubbles due to electrolysis (at around 14.5 volts as several had said).

Reconnected the battery, and it cranked up strongly. Maybe more
strongly than before the incident Took it on several more drives,
same result. I'll occasionally measure the voltage while cranking, that
seems like the best way to measure actual condition.

Thanks to all.

 

[Joe Bramblett, KD5NRH]

Wish I knew. ;-)

Anything that isn't red or black. I hate the red stuff, since when I'm
trying to jump a battery and only have a crappy flashlight handy, the last
thing I need is two red terminals on the same battery.