Slow charging very flat batteries?
Russel McAuliffe
So, I want to slowly charge some batteries I have that are badly
sulphated (many thanks to Gerry Schneider and chris@looneyland for
advice). My battery charger supplies 2.4 amps @ 12v (I assume it
actually supplies more than 12v but I don't trust my crappy analouge
voltmeter). I really need less than 2.4 amps by the sounds of things
(I'll be charging 2 * 6v 60ah batteries in series). I was wondering if I
can use a small 12v 600 milliamp power supply to do a real slow trickle
charge for a few days. My concern is that given 14.2v is the sweet spot
for charging a 12v battery, will charging a battery with 12v do any harm
to the process of desulphating the battery. Is it OK to charge at 12v
for a day or so, then use my 2.4 amp (14v ???) charger for the rest of
the charging?
Many TIA,
Russel McAuliffe.
Gerry Schneider
I think you'll find that the charger won't be a problem - the batts
won't accept very much current at all, and you may have to find a higher
voltage source to even get them going. Once they do start taking current
from the charger, they will automatically control their own "trickle
charge" until they get healthier. My previous reference to current
limiting was assuming a higher voltage "forced current" supply.
--
Gerry
@ Change "not_here" to "lsb"
##_/_\__[(
<0_0_0>
DGoncz
>won't accept very much current at all,
My understanding of lead acid batteries in a state of deep discharge is that
the lead sulphate is insoluble, and that most of the sulphate ions have been
taken from the electrolyte. So the resistance is very high, current is low, and
recharge is very slow, until some ions are present for conduction. Heck, I
recently learned right here in sci.chem.electrochem.battery that the only
reason such a battery works is that the sulphate is insoluble. If it were
soluble, you'd just have an electrochemical reaction cell.
Yours,
Doug Goncz
Replikon Research ( PO Box 4094, Seven Corners, VA 22044-0094 )
This communication is from an inventor, and is for the purpose of
developing an invention. Any information received will be used for that
purpose.
Dyche Anderson
>
> On 31 May 1999 14:34:24 GMT, dgo...@aol.com (DGoncz) wrote:
>
> >My understanding of lead acid batteries in a state of deep discharge is that
> >the lead sulphate is insoluble, and that most of the sulphate ions have been
> >taken from the electrolyte. So the resistance is very high, current is low, and
> >recharge is very slow, until some ions are present for conduction. Heck, I
> >recently learned right here in sci.chem.electrochem.battery that the only
> >reason such a battery works is that the sulphate is insoluble. If it were
> >soluble, you'd just have an electrochemical reaction cell.
>
> with shape changes in the electrodes as they discharge and recharge. that makes
> for a poor battery if long life is expected.
>
> But note, even though still relatively insoluble, the lead compounds formed in a
> completely discharged battery (electrolyte turned essentially to water) are more
> soluble than they are in the acid of a charged cell. This is why the separators
> of such cells are often found blocked with lead sulfate after recovery attempts
> (careful recharge after spiking with a bit of acid) ) have been made.
>
> Recent advice calling for use of very high voltages, like 7 vpc, is very
> destructive to the cells being recovered. So is home made battery formation
> using 50% nitric acid. The poster offering this advice is offering generally
> unsound advice.
>
Research (by the ALABC) has shown that fast charging does help restore sulfated
batteries. However, fast charging means very high currents, NOT very high voltages. The
maximum recommended fast charge voltage is 2.4 to 2.5 V/cell. The maximum practial fast
charge current will vary for each battery, and is a function of cell chemistry, surface
area, and heat rejection capability (and, of course, temperature). I am able to fast
charge a specific 86 amp-hr AGM battery at 150A up to about 70% SOC. I could go as high
as 250A for part of the charge, but system constraints prevent that (I have 39 of them in
series, so the energy required is large).
Dyche Anderson
Gerry Schneider
> Recent advice calling for use of very high voltages, like 7 vpc, is very
> destructive to the cells being recovered.
The high voltage application to get current started through a badly
sulfated cell is as stated in the Gates battery manual for sealed
lead-acid batteries. They recommend a current limit of less than C/20, I
recommended C/100 as a safety measure. They show a typical curve of cell
voltage dropping from above 5V to the normal level over about 48 hours
"as the sulfate crystals convert back to active material and the
impedance of the cell goes down" (quote from the manual).
Would you care to back up your statment about the destructive nature of
this method with facts? Is there some difference between flooded and
sealed battery construction that makes this a good idea in one case and
not in the other?
>So is home made battery formation
> using 50% nitric acid.
They may not have known as much back in 1902 as we do now, but the
Plante lead-acid battery (what the original poster asked for) was in
widespread use. The information is taken directly from "Experimental
Science, Volume One", by George M. Hopkins, "being a collection of
articles originally published in the Scientific American" (quotes are
his). As I said, I haven't used the nitric acid method myself, but the
article states "To hasten the process, the cell is filled with nitric
acid and water equal parts by measure, which is allowed to remain for
twenty-four hours. This preliminary treatment modifies the surface of
the lead, rendering it somewhat porous, and, in connection with the
roughening, reduces the time of formation from four or five weeks to one
week".
Would you care to elaborate on the destructive nature of this method as
applied to solid lead plates?
> The poster offering this advice is offering generally
> unsound advice.
Always willing to be educated by an expert. I'm all ears!
Regards,
Russel McAuliffe
> Recent advice calling for use of very high voltages, like 7 vpc, is very
> destructive to the cells being recovered. So is home made battery formation
> using 50% nitric acid. The poster offering this advice is offering generally
> unsound advice.
Jim, thanks for the tip on the previous advice. Do you have an alternative?
Cheers,
Russel McAuliffe.
Gerry Schneider
> Research (by the ALABC) has shown that fast charging does help restore sulfated
> batteries. However, fast charging means very high currents, NOT very high voltages. The
> maximum recommended fast charge voltage is 2.4 to 2.5 V/cell.
Agreed, which is why I recommended a couple of cycles of "aggressive"
charging at C/3 (for safety) once the batteries were actually able to
take a charge at reasonable voltages. However, the initial state of
severe sulfation will require a high voltage at a low current to start
current flowing. Once the sulfate crystals begin to break down and the
cell impedance drops, then one can switch to more normal charging. This
recommendation is in keeping with information from Gates and from my own
experience with several dozen badly sulfated Gates Cyclon batts.
Russel McAuliffe
> > batteries. However, fast charging means very high currents, NOT very high
> > voltages. The maximum recommended fast charge voltage is 2.4 to 2.5 V/cell.
> Agreed, which is why I recommended a couple of cycles of "aggressive"
> charging at C/3 (for safety) once the batteries were actually able to
> take a charge at reasonable voltages. However, the initial state of
> severe sulfation will require a high voltage at a low current to start
> current flowing.
I hate to admit it, but I'm still not quite clear on charging at different rates such as C/3
etc.If the battery itself determines what current it will take, what is the effect of charging
at different C/x rates. In practical terms: Assume I have a 12v 8 amp battery charger (I can't
even find anyone who sells one higher than that, but anyway...)
For a start I should use 15v (or maybe higher??) to get the process started. I have a 15 v 1
amp power supply. From what I gather, 1 amp is OK to start the process because the current
drain from the battery would be very low as the electrolyte poorly conducts at this stage. Once
the battery starts bubbling well at 15v, I stick my 8 amp charger on the battery. This is
roughly C/7 (60 ah battery). I can't manually adjust this and am assuming the current drain is
completely determined by the state of the battery. I assume my battery will still reach full
charge given enough time even if charging with a 2 amp charger??
I seem to be losing some major point somewhere. Can anyone see where my logic goes wonky? Do I
need a charger that allows me to alter the current, and can someone explain whether and how
"forced current" supplies are different to what I'm talking about.
Cheers,
Russel McAuliffe.
Gerry Schneider
> I hate to admit it, but I'm still not quite clear on charging at different rates such as C/3
> etc.If the battery itself determines what current it will take, what is the effect of charging
> at different C/x rates. In practical terms: Assume I have a 12v 8 amp battery charger (I can't
> even find anyone who sells one higher than that, but anyway...)
Sorry, I'm not meaning to hog the replies, but since I kind of started
the confusion I'll try to clear it up. First of all, a "12V 8amp"
battery charger doesn't put out either 12V or necessarily 8 amps.
Depending on the cost and quality, it either puts out a crude,
semi-controlled voltage and current, or a well-controlled current with
definite voltage monitoring points. The "12V" label just means that it's
designed to charge nominally 12V (6 cell) lead-acid batteries.
The starting point is the battery, which is normally a funny load that
accepts no current at all until you increase the charge voltage to about
2.12 volts per cell (VPC), and then rapidly begins to accept more and
more current as you raise the voltage slightly. Normally, batteries are
charged with a somewhat constant voltage of between 2.2 and 2.5 VPC,
usually with some maximum current limit, until they reach full charge.
Flooded batts like yours then happily go into overcharge and start to
bubble if the rate is too high, which is OK for a while but eventually
causes the electrolyte level to drop and should be discontinued
reasonably soon. Sealed batts that are overcharged too much will die
from venting electrolyte as the pressure release valve opens, so they
need a better grade of charger, of which there are dozens of flavours.
Using a constant voltage charge method allows the battery to accept the
amount of current it needs *to some extent* (high at first, less as it
reaches full charge), but by setting the VPC level (low/medium/high
switch on some chargers), you can determine how fast it gets there,
anything from a C/1000 trickle current to a 10C "boost" charge for some
heavy duty batts.
Normal voltage charging doesn't work well for badly sulfated batteries.
When they've reached this point, a higher voltage must often be applied
to force current into them. The current must be kept small and
controlled either by a current limiter or by monitoring on an ammeter.
As the battery begins to recover, you can see one of 2 things happen. If
using a current limiter, the voltage across the battery will start to go
down as less voltage is needed to drive the current. If using a constant
voltage source, the current will start to go up and you must reduce the
voltage in order to keep the current at a safe level. Once the voltage
drops or is reduced to about 2.5 VPC, the battery is ready to be
discharged a bit and then connected up to a normal charger. You'll need
to charge and discharge it for a couple of cycles to reduce the
sulphation more, and it's recommended that the charge current be fairly
aggressive for the first few cycles. This means setting your charger to
the "high" setting until bubbling occurs. If you just have a single step
charger, you'll still be OK eventually after a dozen or so cycles
(really rough numbers).
Battery charging is actually a somewhat complicated issue, although,
thank goodness, life is pretty simple if the batts are in good shape and
an appropriate charger is used. This will get you to 90% of the optimum
condition, which is good enough for most uses. Getting the other 10%
requires either an intelligent (automatic) charge control and
maintenance system or a dedicated (manual) maintenance regime.
I hope this helped. Feel free to ask more questions, by email if you
prefer (see below).
Russel McAuliffe
> [ Well explained text about battery charging deleted]
> I hope this helped. Feel free to ask more questions, by email if you
> prefer (see below).
OK, So I'm beginning to come to terms with this now. Basically I think I need to buy a better
battery charger as a first step.
You said that normal voltage charging doesn't work well for badly sulphated batteries. Do you (or
anyone else) have a suggestion as a good starting point for v/cell to kick-start the charging
process? Say 4 volts per cell, or should it be a more extreme voltage to begin with?
Many thanks (yet again)
Russel McAuliffe
Russel McAuliffe
Russel McAuliffe wrote:
> You said that normal voltage charging doesn't work well for badly sulphated batteries. Do you (or
> anyone else) have a suggestion as a good starting point for v/cell to kick-start the charging
> process? Say 4 volts per cell, or should it be a more extreme voltage to begin with?
Sorry, found a refernce from Gerry for this ealier on in the thread. Many thanks Gerry..
Russel.
Gerry Schneider
>
> Gerry Schneider wrote:
>
> > [ Well explained text about battery charging deleted]
> > I hope this helped. Feel free to ask more questions, by email if you
> > prefer (see below).
>
> OK, So I'm beginning to come to terms with this now. Basically I think I need to buy a better
> battery charger as a first step.
> anyone else) have a suggestion as a good starting point for v/cell to kick-start the charging
> process? Say 4 volts per cell, or should it be a more extreme voltage to begin with?
>
> Russel McAuliffe
Your present charger will probably be fine once the batts start to
accept some charge (if they ever do - they might just be total junk by
now). You just need to find some way to force some current into them,
and if I remember correctly, the batts are 6V each, so applying the 12V
charger through a 12V auto tail light bulb directly to a single batt
might just get it going. If the lamp begins to glow dimly you'll be in
business. I also believe Jim Higgins or someone else here mentioned
"spiking" the electrolyte with a bit of sulphuric acid to increase
conductivity and get current flowing. Maybe someone here can give you
more details on this.
Gerry Schneider
>
> On Wed, 02 Jun 1999 00:43:18 GMT, Gerry Schneider
> <not_...@sympatico.ca> wrote:
>
> >The starting point is the battery, which is normally a funny load that
> >accepts no current at all until you increase the charge voltage to about
> >2.12 volts per cell (VPC), and then rapidly begins to accept more and
> >more current as you raise the voltage slightly. Normally, batteries are
> >charged with a somewhat constant voltage of between 2.2 and 2.5 VPC,
> >usually with some maximum current limit, until they reach full charge.
>
> I've learned the principles correctly, it would seem that the 2.12
> volt figure above is too low, that the initial voltage to cause
> charging would have to be higher than normal charging at 2.2 to 2.5
> vpc.
>
> Is this a typo, or am I missing something?
I'm not sure if you mean sulfated or healthy batts, so the following is
for healthy batts only. Sulfated batts do need higher initial voltage to
get them started, along with strict limiting of the current flow.
Lead-acid batteries have an open circuit voltage equal to the specific
gravity of their electrolyte plus 850 mV, per cell. For a typical
flooded lead-antimony battery (deep cycle type), the s.g. is 1.265 at
full charge, giving an o.c. voltage of 2.115 VPC. At lower states of
charge, the s.g. and therefore the o.c. voltage is lower by as much as
200 points (200 mV). If you apply a voltage to the battery that's higher
than the o.c. value, charge current will start to flow. If you apply
about 2.2 VPC, the current could be quite high initially if the batt is
depeleted, and some current limiting might need to be applied (normally
built into the charger), but as the battery fills up the current drops,
and eventually reaches a "float" value. The 2.2 VPC is about 85 mV above
the o.c. value, which is considered a good number for long term floating
(75mV to 100mV) of backup batteries, since this low level of overvoltage
minimizes the corrosion of the positive plate due to lead peroxide
buildup. However, this low voltage level isn't that useful for
recovering full charge in batteries that are normally cycled, like
alternate energy applications, so a higher charge voltage is used, up to
about 2.5 VPC, which quickly fills the battery and then begins to
overcharge it. Flooded batteries aren't damaged (much) by reasonable
overcharge, but the voltage, s.g., temp or bubbling rate should be
monitored to figure out that it's time to switch from the rapid charge
down to float charge. This is called "two step charging", and commercial
two step or three step chargers are the best bet to refill batteries
quickly while preventing overcharge. Single one step consumer
(automotive type) chargers will always overcharge, and depend on you to
stop the process.
The above info is sort of simplified, and doesn't deal with temperature
compensation, cell equalization, destratification of electrolyte, etc.,
but following a few of the basic rules will result in a fairly healthy
battery.
Cheers,
Dyche Anderson
>
> I'm beginning to have success with the batteries taking a charge now. I'm just working on a couple of
> batteries at the moment cause I only have two chargers. But I notice the s.g. of the outer cells is
> much more favourable than the inner cells (furthest away from the poles). In the outter cells next to
> the poles I'm getting 1.220 and in the centre cells I get only 1.130 with a rough gradient between
> them. I was just wondering if this is normal or if it indicates a more fundamental problem with those
> cells?
>
> Bring it on Gerry ;-)
>
> Cheers,
> Russel.
I can't remember what the actual type of PbA batteries you have, but if they are of gel or
AGM, try turning the batteries on end so the plates are flat (you can NOT do this with
flooded batteries). Don't laugh. It works wonders with some batteries. What this avoids
is a phenomena known as acid stratification, where acid in the top and bottom of a cell
have different gravities, thus plate utilization is less.
Dyche Anderson
Russel McAuliffe
Gerry Schneider
Dyche mentioned the possibility of electrolyte stratification, which is
a real possibility and can take days to clear up with light charging.
Aggressive charging which bubbles the electrolyte will often stir things
up enough to get better readings, or you could try to take acid samples
from deeper withing the cell.
I don't quite understand your connection. Are you now charging two 6V
batts in series? If by chance you're charging several batts in parallel
then you *must* use corner-connected leads to the charger and use heavy
battery interconnect cables to avoid charging imbalance. I believe this
issue was coverd here about a year ago.
Cheers,
--
Gerry
@ Change "not_here" to "lsb"
##_/_\__[(
<0_0_0> The Hi-Tech Homestead
----------------- http://www3.sympatico.ca/lsb/HOME.HTM
Gerry Schneider
Good advice in one situation applied to a different
> situation can become unsound advice. My earlier remarks were intended in that
> context. If you were offended by them, I sincerely apologize for offending you.
Good grief no, Jim! Just some spirited debate, while some of us (like
me) hopefully learn something.
Russel McAuliffe
Higg...@ftc-i.SpAmZaP.net wrote:
> Russel, I recall you mentioning having flooded batteries. Can you confirm yea
> or nay for future reference?
Yes, flooded 6v. I may have confused things a little because I'm also doing the same thing to a few 12v deep
cycle flooded batteries. I'm beginning to have success with the batteries now. I've got one back to about
40% capactity after 5 cycles so its looking good. I only have a 12v (14v) battery charger so I have to to
the 6v batteries in pairs. The problem with this is that once one battery begins to improve its rate of
increase in capacity increases much faster than the battery in its pair and the gap between them seems to
continue to increase over time.
Cheers,
Russel.
Jean-Pierre Bélisle
Dyche Anderson <dy...@mediaone.net> a écrit dans l'article
<37571B77...@mediaone.net>...
> Russel McAuliffe wrote:
> >
> > I'm beginning to have success with the batteries taking a charge now.
I'm just working on a couple of
> > batteries at the moment cause I only have two chargers. But I notice
the s.g. of the outer cells is
> > much more favourable than the inner cells (furthest away from the
poles). In the outter cells next to
> > the poles I'm getting 1.220 and in the centre cells I get only 1.130
with a rough gradient between
> > them. I was just wondering if this is normal or if it indicates a more
fundamental problem with those
> > cells?
> >
> > Bring it on Gerry ;-)
> >
> > Cheers,
> > Russel.
It may be the internal resistance, because this cell is not directly
connected and is feed through the others,
time on recharge, work and equalisation may flatten this difference. Maybe
a good case in wich the pulsing can help?
Jean-Pierre