That is a good question that demands a good answer.
When lead sulfate builds up and hardens on the battery plates cause the internal resistance to go up. When that happens th ebattery cannot take a charge nor deliver a charge. The SPG falls off the cliff toward neutral.
A battery in good condition meaning cycles and charge properly, the plates deteriorate or dissolve. During the charge cycle both lead and lead sulfate are dissolved from the plates. Th eprocess is reversed during discharge, but not all the lead is re-deposited. You can keep th elead sulfate in check by not over discharging the battery, keeping it fully charged, or let it set long discharged.
Eventually 1 of 2 things happen. You completely disolve the plates which is very rare, or the sulfate eventually builds up on the plates, harden and render the battery useless. 90% of all lead acid battery failures are lead sulfate.
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I have always wondered how the SG can still come up to full value if some of the sulphate in the sulfuric acid has been converted to lead sulfate crystals and taken out of solution?
I would expect that the voltage would rise to the gassing point at "full charge", but the electrolyte SG could not make it back to the original full charge value.
I have seen some members assert that full charge on a 50%-of-original-capacity battery will still correspond to the same SG, rather than just the same voltage. Can you comment on that?
Also, I expect that the answer might be different if the capacity loss is the result of plate shedding or other mechanisms other than sulfation.
As the chemists say, "If you're not part of the solution, you're part of the precipitate."
And that is not intended to be the lead in to a political discussion.
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Sorry but not accurate. Capacity has nothing to do with SOC voltages. You are correct to say as batteries age they loose capacity, no doubt about that. But th eSOC voltage only indicates the percentage of charge, not the capacity. For example the battery may be rated at say 200 AH. But 3 years down the road may only be 150 AH. The SOC would still read 100% at 12.6 volts, but that has nothing to do with the actual capacity.
Only way to determine the capacity is with a capacity load test. Not a DIY project.Leave a comment:
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There are also some graphs available on the web that show voltage versus SOC for a variety of charging and discharging rates expressed as fractions of the 20 hour capacity (C). But given the differences in battery chemistry and construction, these are more useful as a guide to how significantly the charge and discharge rates affect the SOC determination than as an accurate guide for your batteries.
So, as Dereck says, making your own calibration with an accurate ammeter, voltmeter and hydrometer is the best way to get information about your own system.
But the calibration will need to be repeated after (hopefully) a few years as your batteries age and lose capacity.Leave a comment:
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It is fairly correct but there are some caveats.
1. The SOC voltages are completely meaningless on a operating system that is being charged or discharged. The battery has to be disconnected and rested for several hours. However you can get accurate reading SOC voltages on a battery under charge or discharge by making your own chart plotting it with a temperature compensated hydrometer.
2. The voltages are different depending on battery chemistry of AGM, Gel, or on eof the three flooded lead acid types of Lead Calcium, Lead Antimony, or pure Lead. Most all deep cycle FLA batteries are lead antimony.
The voltages the OP list appear to be AGM. FLA will be a bit lower. For example 100% = 12.6
FWIW any quality battery manufacture will list the SOC voltages in the Owners Manual.Leave a comment:
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Got it Thanks
Code:Typical* VRLA Battery Cycling Ability vs. Depth of Discharge Typical Life Cycles Withdrawn Capacity Gel AGM 100% 450 150 80% 600 200 50% 1000 370 25% 2100 925 10% 5700 3100 Flooded acid a little moreLeave a comment:
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If you need to copy in text-formatted tables, putting them in a "Code" section (the "#" sign in the format bar) will allow you to preserve the spacing.
Code:Open Circuit Voltage vs. State of Charge Comparison* % Open Circuit Voltage Charge Flooded Gel AGM 100 12.60 or higher 12.85 or higher 12.80 or higher 75 12.40 12.65 12.60 50 12.20 12.35 12.30 25 12.00 12.00 12.00 0 11.80 11.80 11.80 NOTE: Divide values in half for 6-volt batteries.Leave a comment:
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For Flooded Acid batteries Yes
This might be a helpful read:
http://www.evdl.org/docs/deka-vrr.pdf
Open Circuit Voltage vs. State of Charge Comparison*
% Open Circuit Voltage
Charge
Flooded Gel AGM
100 12.60 or higher 12.85 or higher 12.80 or higher
75 12.40 12.65 12.60
50 12.20 12.35 12.30
25 12.00 12.00 12.00
0 11.80 11.80 11.80
NOTE: Divide values in half for 6-volt batteries.
* The “true” O.C.V. of a battery can only be determined after the battery
has been removed from the load (charge or discharge) for 24 hours.Leave a comment:
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DOD and voltage chart.
Is this chart correct?
Is SOC inversely proportional to DOD or is it more complicated?
This is for a lead acid battery.
SOC 12V battery 24V battery DOD
100% 12.70+ 25.4+V 0%
75% 12.40 24.8V 25%
50% 12.20 24.4V 50%
25% 12.00 24V 75%
0% 11.80 22.6V 100%
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