On Saturday, March 30, 2019 at 9:10:06 AM UTC-7, bill....@ieee.org wrote:
> 
> Chemical reactions do tend to get slower at lower temperatures, but this doesn't seem to be a problem with batteries. Electrolytes get more resistive at low temperatures, which can be more of a problem.
> -- 
> Bill Sloman, Sydney

I found some information on the temperature compensation used with lead-acid batteries. The temperature compensation defines the maximum charge voltage per cell and the float voltage per cell for any specified temperature. The objective is to prevent overcharging and extend the life of the battery.

Car batteries are typically exposed to ambient temperatures in the range of -40 to +120 degrees F. Discharge capacity is reduced at low temperatures and I suspect that charging is less effective even with the temperature compensation. It makes you wonder if car batteries were being charged adequately in the recent very cold winter.

The logarithmic relationship you mentioned is quite interesting and does seem to explain the sensitivity in the voltage readings.

Thanks for both of your replies.

On Wednesday, April 18, 2018 at 4:14:50 AM UTC+10, kt77 wrote:
> The concept of measuring battery voltage to indicate state of charge may not be very precise. This morning I measured my battery voltage at the battery terminals 36 hours after removing my battery maintainer. The voltage read 12.70 volts. I then opened the driver side car door which apparently results in some current flow. The battery voltage dropped to 12.60 volts and then drifted down to 12.48 volts within a few minutes.
> 
> After closing the car door, the voltage drifted back up to 12.68 volts after about 25 minutes. I've checked this battery on quite a few occasions and temperature also seems to be a factor. It's not clear if voltage readings are any more meaningful at lower states of charge. The table I have been referencing shows 100% charge at 12.7 volts, 75% charge at 12.4 volts, 50% charge at 12.2 volts, 25% charge at 12.0 volts, and 0% charge at 11.9 volts.

https://www.doitpoms.ac.uk/tlplib/batteries/thermodynamics.php

Battery voltage is a logarithmic function of reagent concentration. When a battery is close to fully charged there's not a lot of the unchanged reagent, and a lot of the charged reagent, and it doesn't take much discharge to shift the voltage appreciably.

It's also a function of battery temperature, which goes up a bit - due to ohmic heating - whenever you pull charge out of it.

The voltage you read at the terminals can drift around a bit for all sorts of reasons.

-- 
Bill Sloman, Sydney

On Saturday, March 30, 2019 at 5:38:49 AM UTC+11, kt77 wrote:
> Charging systems typically increase the charge voltage at lower temperatures. Does anyone know if the increased voltage fully compensates at low temperatures? One would think that the chemical reactions would be slowed considerably.

The free energy of the chemical reaction involved does depends on temperature.

Chemical reactions do tend to get slower at lower temperatures, but this doesn't seem to be a problem with batteries. Electrolytes get more resistive at low temperatures, which can be more of a problem.

<snip>

-- 
Bill Sloman, Sydney

Charging systems typically increase the charge voltage at lower temperatures. Does anyone know if the increased voltage fully compensates at low temperatures? One would think that the chemical reactions would be slowed considerably.

I recently discovered that my Black & Decker 2 amp charger is not temperature compensated and it also does not have a constant voltage phase for saturation of the battery. At lower temperatures, the 2 amp constant current charge results in surface charge building up rapidly and the unit switches to float mode prematurely.

I also have the new switching version of the Battery Tender Plus which previously was a linear design. The charger is now temperature compensated. This device does implement the constant current and constant voltage phases for saturation of the battery.

Lastly, I recently tested the new CTEK MXS 5.0 charger which is quite impressive. It has an eight stage charging algorithm with optional reconditioning mode. The saturation phase can take several hours at 14.5 volts or higher. After monitoring these chargers, I can now see the significant limitations in my car's charging system.

The concept of measuring battery voltage to indicate state of charge may not be very precise. This morning I measured my battery voltage at the battery terminals 36 hours after removing my battery maintainer. The voltage read 12.70 volts. I then opened the driver side car door which apparently results in some current flow. The battery voltage dropped to 12.60 volts and then drifted down to 12.48 volts within a few minutes.

After closing the car door, the voltage drifted back up to 12.68 volts after about 25 minutes. I've checked this battery on quite a few occasions and temperature also seems to be a factor. It's not clear if voltage readings are any more meaningful at lower states of charge. The table I have been referencing shows 100% charge at 12.7 volts, 75% charge at 12.4 volts, 50% charge at 12.2 volts, 25% charge at 12.0 volts, and 0% charge at 11.9 volts.

On 02/10/2018 10:45 PM, Steve Wilson wrote:
> oldschool@tubes.com wrote:
> 
>> On Sat, 10 Feb 2018 20:18:31 GMT, Steve Wilson <no@spam.com> wrote:
>   
>>> My previous car was a Ford Taurus. It was designed to destroy the battery,
>   
>> A mechanic once told me. There are TWO four letter "F-Words". He allows
>> his children to say the first one, but not the word FORD. (Unless the
>> first four letter F-Word, precedes the word FORD).
>   
> The Taurus had another built-in failure mode designed to destroy the engine
> through loss of coolant. Here is the story:
> 
> https://silvercell.000webhostapp.com/car/taurus.htm
> 
> A fiendish wicked design. It is now 2018. I don't see any more on the road
> these days. They either rusted out or lost the engine.

BITD the Taurus SHO was a beast.  Complete stealth family car that would 
blow the doors off just about anything out there.

Cheers

Phil Hobbs

-- 
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net

On 02/10/2018 08:35 PM, Jim Thompson wrote:
> On Sat, 10 Feb 2018 20:13:52 -0500, krw@notreal.com wrote:
> 
>> On Sat, 10 Feb 2018 19:53:02 -0500, Phil Hobbs
>> <pcdhSpamMeSenseless@electrooptical.net> wrote:
>>
>>> On 02/10/18 19:44, krw@notreal.com wrote:
>>>> On Sat, 10 Feb 2018 16:42:42 -0500, Phil Hobbs
>>>> <pcdhSpamMeSenseless@electrooptical.net> wrote:
>>>>
>>>>> On 02/10/2018 04:18 PM, oldschool@tubes.com wrote:
>>>>>> On Sat, 10 Feb 2018 20:18:31 GMT, Steve Wilson <no@spam.com> wrote:
>>>>>>
>>>>>>> My previous car was a Ford Taurus. It was designed to destroy the battery,
>>>>>>
>>>>>> A mechanic once told me. There are TWO four letter "F-Words". He allows
>>>>>> his children to say the first one, but not the word FORD. (Unless the
>>>>>> first four letter F-Word, precedes the word FORD).
>>>>>
>>>>> I have two of them, a convertible stick-shift Mustang (my car, which I
>>>>> love) and a turbo-four Fusion (my wife's car, whose dashboard displays I
>>>>> cordially dislike, but which makes her happy).  No worries so far.
>>>>
>>>> I have two, also.  My wife's car is also a convertible Mustang (though
>>>> a 6-speed auto) and I drive an F-150 (bought both the same week ;-).
>>>> She had a Mercury Sable (same car as the Ford Taurus) and had no
>>>> problems with batteries.  We were in Vermont at the time and got seven
>>>> years out of the original). Great vehicles.  The only crappy Ford I've
>>>> had was the '73 Rustang-II (i.e. Pinto, in drag). OTOH, every Chrysler
>>>> product I've had was crap.
>>>>
>>>
>>> We had a '94 Dodge Grand Caravan, which was great until it finally
>>> rusted out circa 2003.  It had far and away the most comfortable seats
>>> of any vehicle I've ever driven, and it was very reliable mechanically.
>>
>> I had '85 and a '90 voyagers.  Both rusted badly.  The '85 went
>> through a head gasket every 30K miles (you could set a watch by it).
>> Both rusted out before 100K miles (about six years).  The NE is hard
>> on car bodies but they weren't that much better than the Rustang-II.
>>
>> I also had a '93 Eagle Vision TSI and a '96 Chrysler Intrepid.  Nice
>> comfortable cars but they fell apart.  The final nail for both was
>> transmissions.
>>
>>> OTOH my '92 Saturn SC lasted twice as long before succumbing to
>>> corrosion. (It was old enough to drive itself.)
> 
> Car restorers/collectors buy engines from the Northeast and bodies
> from Arizona or Southern California.
> 		
>                                          ...Jim Thompson
> 

Seems like less of a problem nowadays.  We just got rid of a 2004 
Hyundai XG350 because the fenders rusted out, but it had 180k on it and 
didn't owe us anything--apart from one engine computer and a set of 
struts it worked fine till the day we traded it in on the Fusion.

Cheers

Phil Hobbs

-- 
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net

kt77 <kawill70@gmail.com> wrote:

> On Friday, February 9, 2018 at 2:29:37 PM UTC-8, Steve Wilson wrote:

>> 2. when the engine is running, the alternator quickly charges the
>> battery 

>> to capacity, then the charging current drops to near zero, in the tens
>> of 
>> milliamperes range. Modern engines start so quickly that very little
>> ener gy  is needed to start the car. 

> I agree if the voltage regulator settings allow it.  The problem today
> is that new cars are often light on charging to reduce alternator load
> and increase fuel economy.  My car is in that category and the highest
> alternator voltage I've seen after a cold start is 14.25 volts and that
> was on a cold day.  As soon as the engine warms up the voltage drops to
> the range of 13.5-13.8 volts.  I may only see ten minutes where the
> charge current would be adequate for charging the battery.  Ten minutes
> appears to be fine if the battery is in good condition and near full
> charge.  It's a different story with a discharged battery or a sulfated
> battery.  I think others have stated that automotive charging systems
> today are not designed to recharge a discharged battery. 

> I also wonder if there is a secondary problem with the temperature
> compensation typically used with voltage regulators.  If I restart my
> car after a short trip, the engine is still warm and the alternator
> voltage may be 13.8 volts or less.  The battery may still be relatively
> cool inside and need a higher alternator voltage to charge adequately. 

With the proper charging voltage, the battery recharges quickly after 
starting the engine. The actual drain current to keep the battery charged 
is very low. However, when you have a high load current from headlights, 
heatd seats, rear window defrost, stereo, and other loads, the alternator 
only charges on the peaks, and the battery has to supply the total load 
current between the peaks.

The alternator output is three phase bridge rectified, so there are 6 
voltage peaks per cycle. This means the ripple voltage is pretty low, so 
the alternator is taking the full load for a large part of the cycle. But 
the battery has to supply the load the rest of the time, and it needs to be 
in good shape. Especially if you are stuck in traffic at night with the 
healights on and the air conditioning full on. My battery died in Toronto 
one night under these same conditions, and it was a real pain trying to get 
it out of the traffic and get the engine started again.

Older cars had the voltage regulator inside the alternator. Since the 
alternator was bolted to the engine, it quickly attained the heat from the 
engine. After warmup, the regulator reduced the charging voltage regardless 
of the actual battery temperature. The battery became depleted and would 
begin to sulfate. This happened on my old Taurus. 

Newer cars meaure the intake manifold air temperature to estimate the 
battery temperature. This is a bit more accurate, but the temperature 
sensor can absorb heat from the engine while you are shopping. This throws 
off the estimate of battery temperature and the battery can be overcharged 
or undercharged depending on conditions.

oldschool@tubes.com wrote:

> On Sat, 10 Feb 2018 20:18:31 GMT, Steve Wilson <no@spam.com> wrote:

>>My previous car was a Ford Taurus. It was designed to destroy the battery, 

> A mechanic once told me. There are TWO four letter "F-Words". He allows
> his children to say the first one, but not the word FORD. (Unless the
> first four letter F-Word, precedes the word FORD). 

The Taurus had another built-in failure mode designed to destroy the engine 
through loss of coolant. Here is the story:

https://silvercell.000webhostapp.com/car/taurus.htm

A fiendish wicked design. It is now 2018. I don't see any more on the road 
these days. They either rusted out or lost the engine.

"Tim Williams" <tiwill@seventransistorlabs.com> wrote:

> "Steve Wilson" <no@spam.com> wrote in message 
> news:XnsA8859BBAA996Eidtokenpost@69.16.179.23...

>> I don't think you can attribute your performance to sulfation - the 
>> battery has to be almost dead and sitting for guite some time. Then it
>> won't  accept a charge. 

> "Sulfation" in a weak sense, in that, that's simply how a lead acid
> works (PbSO4 and Pb <--> Pb and PbO2), but that it's probably nonuniform
> enough to cause problems (high ESR) but apparently not beyond the point
> of no return. 
> Tim

The equation  we are interested in is

Pb(s) + PbO2(s) + 2H2SO4(aq) --> 2PbSO4(s) + 2H2O(l)

Both plates get sulfated. This is not bad if the battery gets fully charged 
before the sulfur crystals have time to harden. Here are some articles that 
describe it better:

  BU-804b: Sulfation and How to Prevent it

  Applying ways to minimize sulfation.

  Sulfation occurs  when  a lead acid battery is  deprived  of  a full
  charge. This is common with starter batteries in cars driven  in the
  city with  load-hungry accessories. A motor in idle or at  low speed
  cannot charge the battery sufficiently.

  Electric wheelchairs have a similar problem in that the  users might
  not charge  the  battery long enough. An  8-hour  charge  during the
  night when the chair is not being used is not enough. Lead acid must
  periodically be charged 14 - 16 hours to attain full saturation.

  This may  be the reason why wheelchair batteries last only  2 years,
  whereas golf  cars  with  the identical  battery  deliver  twice the
  service life.  Long leisure time allows golf car batteries to  get a
  full charge overnight. (See 403: Charging Lead Acid.)

  Solar cells  and  wind  turbines do  not  always  provide sufficient
  charge for  lead  acid  banks, which  can  lead  to  sulfation. This
  happens in  remote parts of the world where villagers  draw generous
  amounts of  electricity  with  insufficient  renewable  resources to
  charge the  batteries.  The result is a short battery  life.  Only a
  periodic fully  saturated charge can solve the problem.  But without
  an electrical grid at their disposal, this is almost impossible.

  An alternative solution is using lithium-ion, a battery that prefers
  a partial  charge  to a full charge. However,  Li-ion  is  more than
  double the  cost  of lead acid. Although more  expensive,  the cycle
  count is  said to be cheaper than that of lead acid  because  of the
  extended service life.

  What is  sulfation?  During use, small  sulfate  crystals  form, but
  these are  normal  and  are  not  harmful.  During  prolonged charge
  deprivation, however,  the  amorphous  lead  sulfate  converts  to a
  stable crystalline  and deposits on the negative plates.  This leads
  to the  development  of  large crystals  that  reduce  the battery's
  active material, which is responsible for the performance.

  There are  two types of sulfation: reversible  (or  soft sulfation),
  and permanent  (or hard sulfation). If a battery is  serviced early,
  reversible sulfation  can   often   be   corrected   by  applying an
  overcharge to  an  already fully charged battery in  the  form  of a
  regulated current  of about 200mA. The battery  terminal  voltage is
  allowed to rise to between 2.50 and 2.66V/cell (15 and 16V on  a 12V
  mono block)  for about 24 hours. Increasing the  battery temperature
  to 50 - 60C (122 - 140F) during the corrective service further helps
  in dissolving the crystals.

  Permanent sulfation  sets  in  when the battery has  been  in  a low
  state-of-charge for  weeks  or  months. At this  stage,  no  form of
  restoration seems possible; however, the recovery yield is not fully
  understood. To  everyone's  amazement, new lead  acid  batteries can
  often be  fully restored after dwelling in  a  low-voltage condition
  for many weeks. Other factors may play a role.

  A subtle  indication  whether lead acid can be recovered  or  not is
  visible on  the voltage discharge curve. If a fully  charged battery
  retains a   stable   voltage   profile   on   discharge,  chances of
  reactivation are better than if the voltage drops rapidly with load.

  Several companies offer anti-sulfation devices that apply  pulses to
  the battery  terminals  to   prevent   and  reverse  sulfation. Such
  technologies will lower the sulfation on a healthy battery, but they
  cannot effectively  reverse the condition once present. It's  a "one
  size fits all" approach and the method is unscientific.

  Applying random  pulses or blindly inducing an  overcharge  can harm
  the battery by promoting grid corrosion. There are no simple methods
  to measure  sulfation,  nor are commercial  chargers  available that
  apply a  calculated  overcharge to dissolve  the  crystals.  As with
  medicine, the most effective remedy is to apply a corrective service
  for the time needed and not longer.

  While anti-sulfation devices can reverse the condition, some battery
  manufacturers do  not recommend the treatment as it tends  to create
  soft shorts  that  may   increase  self-discharge.  Furthermore, the
  pulses contain  ripple  voltage  that  causes  some  heating  of the
  battery. Battery  manufacturers  specify the  allowable  ripple when
  charging lead acid batteries.

  Last updated 2016-09-22

http://batteryuniversity.com/index.php/learn/article/sulfation_and_how_to_p
revent_it
  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  Discharge

  In the discharged state both the positive and negative plates become
  lead(II) sulfate  (PbSO4),  and the electrolyte  loses  much  of its
  dissolved sulfuric  acid and becomes primarily water.  The discharge
  process is  driven by the conduction of electrons from  the negative
  plate back  into  the  cell at the positive  plate  in  the external
  circuit.

  The total reaction can be written as

  Pb(s) + PbO2(s) + 2H2SO4(aq) --> 2PbSO4(s) + 2H2O(l)

  Sulfation and desulfation

  Lead -  acid  batteries  lose the ability to  accept  a  charge when
  discharged for  too  long due to sulfation,  the  crystallization of
  lead sulfate.[27] They generate electricity through a double sulfate
  chemical reaction.  Lead and lead dioxide, the  active  materials on
  the battery's plates, react with sulfuric acid in the electrolyte to
  form lead sulfate. The lead sulfate first forms in a finely divided,
  amorphous state,  and  easily  reverts  to  lead,  lead  dioxide and
  sulfuric acid when the battery recharges. As batteries cycle through
  numerous discharges and charges, some lead sulfate is not recombined
  into electrolyte  and slowly converts to a  stable  crystalline form
  that no  longer dissolves on recharging. Thus, not all  the  lead is
  returned to  the  battery plates, and the  amount  of  usable active
  material necessary for electricity generation declines over time.

  Sulfation occurs in lead - acid batteries when they are subjected to
  insufficient   charging   during   normal   operation.   It  impedes
  recharging; sulfate deposits ultimately expand, cracking  the plates
  and destroying the battery. Eventually so much of the  battery plate
  area is  unable  to  supply current  that  the  battery  capacity is
  greatly reduced.  In  addition,  the sulfate  portion  (of  the lead
  sulfate) is not returned to the electrolyte as sulfuric acid.  It is
  believed that  large crystals physically block the  electrolyte from
  entering the  pores of the plates. Sulfation can be  avoided  if the
  battery is fully recharged immediately after a discharge cycle.[28]

  A white  coating  on the plates may be  visible  (in  batteries with
  clear cases,  or after dismantling the battery). Batteries  that are
  sulfated show  a  high internal resistance and  can  deliver  only a
  small fraction  of normal discharge current. Sulfation  also affects
  the charging  cycle,  resulting   in   longer  charging  times, less
  efficient and incomplete charging, and higher battery temperatures.

  SLI batteries  (starting,  lighting,  ignition;  ie,  car batteries)
  suffer most deterioration because vehicles normally stand unused for
  relatively long  periods  of  time.   Deep  cycle  and  motive power
  batteries  are   subjected   to   regular   controlled overcharging,
  eventually failing  due  to corrosion of  the  positive  plate grids
  rather than sulfation.

  There are  no   known,   independently   verified   ways  to reverse
  sulfation.[8][29] There are commercial products claiming  to achieve
  desulfation through various techniques (such as pulse charging), but
  there are no peer-reviewed publications verifying their claims.

  Sulfation prevention  remains   the   best   course   of  action, by
  periodically fully charging the lead-acid batteries.

  https://en.wikipedia.org/wiki/Lead%E2%80%93acid_battery

So when you go to Walmart or some other battery store, you may see racks of 
batteries waiting to be sold. The reason they don't sulfate is because they 
were fully charged before being placed on the racks, and they don't stay 
there long enough to become discharged.