battery bank 12.9, hydrometer in red???

[SoulRaven]

Confusion is reigning in my camp ....

I have 2 Duracell SLIGC115 batteries wired in series.  

duracell spec from Batteries plus

I have felt that there is a problem with them, so at this time, they are getting no use.  I have them being recharged by a solar trickle charger.  

amazon description of charger

When I read the voltage using a multimeter, it reads 12.9 ... yet when I use a hydrometer to check State of Charge, IT reads in the red; 12.5 ... 

It seems to me that is a problem... Do you experts agree?

Thanks,

Pat

 

[SoulRaven]

Well, a big DUH from Pat.... 
:blush: :s

I forgot to factor in the temperature ... according to the hydrometer, I should add "4"... I'm going to assume that is .4 .  In which case, the hydrometer is reading 12.9 , which agrees with the multimeter.

Thanks ,

Pat

 

[jimindenver]

First question is why are you using that trickle charger when you have a panel up top? Second is if they are getting no use, what is running the trailer. Last is why do you think there is a issue with the batteries?

 

[Spaceman Spiff]

 . . . When I read the voltage using a multimeter, it reads 12.9 ... yet when I use a hydrometer to check State of Charge, IT reads in the red; 12.5 ... 
It seems to me that is a problem... Do you experts agree?

I forgot to factor in the temperature ... according to the hydrometer, I should add "4"... I'm going to assume that is .4 .  In which case, the hydrometer is reading 12.9 , which agrees with the multimeter.

First, some questions:

1. Is the trickle charger connected and charging when taking the measurement?  If it is you are measuring the voltage of the charger.
2. Is the hydrometer free floating?  If the float is touching the top plug it will be pushed down and read low, if touching the bottom it will read high, if it sticks to the side it will read incorrectly.
3. Have you measured the battery voltage after it has rested (no current in or out) for at least 8 hours?

Also, hydrometer reading is 1.XXX and the temperature adjustment is in 0.0XX.  So your reading would be 1.25? ± .004

Disconnect the battery from all loads and let the battery sit more than 8 hours.  Measure voltage across the two terminals.  A good, fully charged battery should measure ~ 12.7V and hydrometer reading should be around 1.270 (temp corrected) and the cells should not vary more than ±0.005.

 

[SoulRaven]

First, some questions:

1. Is the trickle charger connected and charging when taking the measurement?  If it is you are measuring the voltage of the charger.
2. Is the hydrometer free floating?  If the float is touching the top plug it will be pushed down and read low, if touching the bottom it will read high, if it sticks to the side it will read incorrectly.
3. Have you measured the battery voltage after it has rested (no current in or out) for at least 8 hours?

1.  No
2. Yes
3. Yes

Thanks

Pat

 

[SoulRaven]

First, some questions:

1. Is the trickle charger connected and charging when taking the measurement?  If it is you are measuring the voltage of the charger.
2. Is the hydrometer free floating?  If the float is touching the top plug it will be pushed down and read low, if touching the bottom it will read high, if it sticks to the side it will read incorrectly.
3. Have you measured the battery voltage after it has rested (no current in or out) for at least 8 hours?

Also, hydrometer reading is 1.XXX and the temperature adjustment is in 0.0XX.  So your reading would be 1.25? ± .004

Disconnect the battery from all loads and let the battery sit more than 8 hours.  Measure voltage across the two terminals.  A good, fully charged battery should measure ~ 12.7V and hydrometer reading should be around 1.270 (temp corrected) and the cells should not vary more than ±0.005.

Now that I have a laptop instead of a tablet, I can answer more thoroughly.   I did give the battery 8 hours since the sun went down.  It was still dark when I checked it.  There was and is no load on it at all.  

The sun is now up, even though it's really cloudy here in this part of AZ.  I will disconnect it, and check it again.  

In regard to Jim's question, I would prefer to not cloud this issue with why I'm doing this when I have that , etc....

I wish to focus on this behavior regarding different readings from my multimeter and the hyrdometer.  I have had it drummed into me since the 7th grade to eliminate as many variables as possible when you are trying to understand some kind of behavior, whether it's rats or robots.   

I have noticed some behavior in my solar power system that seems odd, and I wish to understand it.   For myself.  So, I hope to pursue an answer using methods that I have found to be tried and true.

Thanks for your help,

Pat

 

[Spaceman Spiff]

Confusion is reigning in my camp ....
When I read the voltage using a multimeter, it reads 12.9 ... yet when I use a hydrometer to check State of Charge, IT reads in the red; 12.5 ... 

Confusion reigning here too.  I pulled out my hydrometer (turkey baster type with thermometer).  Green goes from 1.300 to 1.260, white goes from 1.260 to 1.225 and red from 1.225 to 1.000.  A battery at 1.25 should be at ~85%, a battery at 1.22 is at ~ 50%.

Battery specific gravity is defined at 80ºF, add 0.004 to reading for every 10ºF above and subtract 0.004 for every reading 10ºF below.  Your battery electrolyte at 90ºF?  With a trickle charge they shouldn't be heating up at all; should be close to ambient.

 

[SoulRaven]

Confusion reigning here too.  I pulled out my hydrometer (turkey baster type with thermometer).  Green goes from 1.300 to 1.260, white goes from 1.260 to 1.225 and red from 1.225 to 1.000.  A battery at 1.25 should be at ~85%, a battery at 1.22 is at ~ 50%.

Battery specific gravity is defined at 80ºF, add 0.004 to reading for every 10ºF above and subtract 0.004 for every reading 10ºF below.  Your battery electrolyte at 90ºF?  With a trickle charge they shouldn't be heating up at all; should be close to ambient.

I must have misread the hydrometer.  You know, I need reading glasses for that stuff.

God, I'm old.  I had to get my little magnifying glass with a light to read the hydrometer gradations (right term?) ... where it reads is 1200... the white is 1250.

So, it still doesn't agree with the multimeter or the load meter I just bought.  

load meter


so, it still needs recharging, even though the multimeter reads 12.8 after a day of doing nothing.

 

[Trebor English]

When the battery is charged the plates are lead and lead oxide and the electrolyte is sulfuric acid.  When you take electricity the lead becomes lead sulfate and the electrolyte becomes water.  The lead sulfate layer goes deeper as electricity use continues.  As the layer of lead sulfate gets thicker the battery voltage drops as the electricity is harder to get out through the lead sulfate.

When the battery gets charged the lead sulfate plates give up the sulfur and the electrolyte becomes stronger sulfuric acid.  That happens first on the outer most surface of the plates.  That will give a 12.9 volt reading quickly.  Water has a specific gravity of 1.000.  As the electrolyte gets more sulfur it gets denser.  When the plates have lead sulfate buried under lead that resulted from charging it takes more pressure, voltage, to get that buried lead sulfate out and back into the electrolyte.   More charging gets the buried lead sulfate converted and gets that sulfur back into the acid making it denser.  1.275 to 1.280 means the electrolyte is back to full strength acid.  

We can't measure the lead sulfate layer thickness.  Measuring specific gravity of the electrolyte tells how much sulfur is missing.  What's missing from the acid is on the plates.

Meanwhile the voltage depends on the charged lead outer surface of the plate.  The actual state of charge can be measured by checking the density of the acid.  Buried lead sulfate means less sulfur in the acid, less dense acid.  The volt meter doesn't measure state of charge.  It only responds to the outer most surface of the plates.  

Usualy partial state of charge cycling, PSOC cycling, results in buried lead sulfate.  Fully charging gets all of the lead sulfate back to lead.  A charge that is only 80% leaves some lead sulfate.  The part that is left is buried under a layer of charged lead.  The next 80% discharge / charge cycle leaves more lead sulfate buried.  

The volt meter and the hydrometer measure different things.  Compared to a normal battery a sulfated battery will have a high voltage, lower specific gravity and lower capacity.  It will charge up quickly and run down quickly.

 

[SoulRaven]

Thanks,  Trebor.  I could actually understand that.

 

[SoulRaven]

{BIG snip}

The volt meter and the hydrometer measure different things.  Compared to a normal battery a sulfated battery will have a high voltage, lower specific gravity and lower capacity.  It will charge up quickly and run down quickly.

Dear moderators, could we possibly make the above post by Trebor English a sticky ?  I found it to be extremely helpful and clear. 

Thanks, 

Pat

 

[Tinysolarshack]

I didn’t see this mentioned but a “12v battery “ is technical in a deep state of discharge at 12.1-2 volts. Use below those numbers will seriously reduce battery life. The proper input charge voltage should be 13.8 volts from your solar panels/ charge controller. A fully charged 12 v battery should have a nominal voltage in the range of 13.5 volts.
Given that you are dealing with a sulphated cell condition,you might need a stronger charger to break the sulphation loose and get the chemistry back in line. Try to never leave a battery in a discharged state for very long. Batteries are like people they need exercise ow and then to stay healthy ? peace Bryan

 

[John61CT]

Lots of misinformation there.

But the OP is well on his way to knowing what he's doing.