Battery lifetime/cost vs. state of charge

[kmacdonald]

Originally Posted by valhalla360

Nope, you have plenty of speculation and your results are not consistent with the graphs put out by the manufacturers. (see post 112 which shows how it produces more overall amp-hrs). The big issue is all of these charts assume 100% charge between cycles. Also, they don't say but they most likely accelerate the testing by starting the charge as soon as the DOD is reached so you aren't likely seeing comparable results where there are typically at least a few hours early morning where the bank sits partially discharged.

Basically, the 50% DOD is a compromise between maximizing total amp-hrs over the life of the batteries versus keeping the battery bank size reasonable. It also gives you a nice reserve capacity for use in emergencies.

With 80% discharge you give up some amp-hrs over the life of each battery and if anything goes wrong, you are far more likely to run them dead. Let's say your fridge thermostat sticks on in the early evening. With 50% discharge, odds are you find out in the morning when your food is frozen and the batteries are still at 20-40% charge. If you plan on 80% discharge, you likely have 0% charge (and damaged batteries) by morning.

Actually there is no speculation on my part. The data I used was from Trojan and I posted the link to it. Your comment that it was not consistent is not correct and your false comments cloud a rational discussion.

[Maine Sail]

Originally Posted by kmacdonald

The capacity lost due to PSOC happens regardless of the DOD.

Yes but what I see in testing (real world) is that Ah capacity loss it is greatly accelerated as the real world DOD cycles go deeper.

Originally Posted by kmacdonald

If you recharge to full after each use PSOC degradation doesn't happen.

If you recharge after each use you are not really PSOC cycling you are just real world cycling. Even real world cycling, minus PSOC use, dose not match lab data.

The time at heavy sulfation before full recharge, as well as the discharge rate, as well as your absorption cycle duration and voltage still affects the battery.

We need to move away from thinking and believing this BCI test lab data until the manufacturers and the BCI are willing to develop and use real world testing criteria or they can develop a PSOC resistance test.

[kmacdonald]

Originally Posted by mvas

Why is your chart from Trojan, for their T-105RE, which includes CARBON (like the FireFly), the best chart, but charts from other manufacturer's are only speculation?
Are saying that the majority of the batteries in use, now include carbon?

I used the chart for the T-105RE because I feel it is the best LA battery for marine use.

The PSOC argument holds true regardless of DOD. It does nothing to support a 50% DOD max.

[valhalla360]

Originally Posted by kmacdonald

The capacity lost due to PSOC happens regardless of the DOD. If you recharge to full after each use PSOC degradation doesn't happen.

Big difference sitting at 50% PSOC vs 20% PSOC for several hours per day but hey, I'm don't have to replace your battery bank, so have at it.

[kmacdonald]

What this thread really shows is the superiority of lithium batteries for marine use. Lets discuss whether a BMS is necessary.

[valhalla360]

Originally Posted by kmacdonald

Actually there is no speculation on my part. The data I used was from Trojan and I posted the link to it. Your comment that it was not consistent is not correct and your false comments cloud a rational discussion.

You are speculating that the test numbers are comparable to real world use and trying to state it as a proven fact when you have provided no data to confirm this.

Also, the other graphs provided by the manufacturers are not consistent with numbers you are telling us 3rd hand which hardly makes them "fact".

[kmacdonald]

Originally Posted by valhalla360

You are speculating that the test numbers are comparable to real world use and trying to state it as a proven fact when you have provided no data to confirm this.

Also, the other graphs provided by the manufacturers are not consistent with numbers you are telling us 3rd hand which hardly makes them "fact".

If the test numbers are incorrect for 80% DOD then it stands to reason they are equally incorrect for 50% DOD. I never said they were comparable to real world numbers but said it is the best available data.
In the real word everyones battery usage will vary and decisions will need to be made on that individual use profile. Discharging to 80% DOD should not be automatically excluded from consideration and may make sense under certain conditions. It's really not a simple binary decision everyone here seems to be looking for.

[Maine Sail]

Originally Posted by kmacdonald

If the test numbers are incorrect for 80% DOD then it stands to reason they are equally incorrect for 50% DOD.

They are just incorrect for real world use.

Originally Posted by kmacdonald

Discharging to 80% DOD should not be automatically excluded from consideration and may make sense under certain conditions.

Absolutely!

The best testing data we have today are the PV IEC tests but many manufacturers are resistant to the IEC test and they too are not very "real world" and extrapolate a bit much..

They do include some PSOC use but again it not very realistic or real world though far better than the garbage testing the BCI uses..

Sadly the Ah capacity data under this test is exaggerated at 40C/104F and the testing usually only lasts for 15 months so it is not very representative of "real world" and completely ignores calendar life at elevated temps.

IEC testing also suggests/extrapolates that 100 shallow "micro cycles" plus 50 deep "macro cycles" (150 total cycles a mix of 50 deep and 100 shallow) equal 365 days worth of solar use in the real world. Still if all manufactures tested to this standard we'd have a slightly better idea how certain batteries deal with that particular testing.

[mvas]

Originally Posted by kmacdonald

Wrong. Get your facts straight. Here is the link: http://www.trojanbattery.com/pdf/dat...ata_Sheets.pdf

The chart is not logarithmic so maybe that will help you understand a little better.

You have made an incorrect assumption about the Trojan Chart.
That DOD Chart that you quote from Trojan does not contain any real data.
It is for "Estimation Purposes" only.
There are no facts in that chart.

It is simply the graph of this inverse relationship formula:
#Cycles = 80,000 / DOD
=======================

• 4,000 cycles = 80,000 / 20 (% DOD)
• 2,000 cycles = 80,000 / 40 (% DOD)
• 1,000 cycles = 80,000 / 80 (% DOD)
• .. 800 cycles = 80,000 / 100 (% DOD)

Therefore, when you multiply "Cycles x % DOD" from that chart
you will always get the Constant = 80,000.
Re-computing the constant from the formula, proves absolutely nothing.
Your chart does not indicate the actual # of deep cycles per any real test.

Your false statements have clouded the facts.

The DOD Chart in message # 13 ...
has real data points, from real battery tests, with a best fit curve overlay.
That chart does show the accelerated reduction in cycles for deeper DOD.

[kmacdonald]

Post deleted by mods.

[kmacdonald]

Of course the total energy stored in a battery over its useful life is a constant. It's not a function of DOD. Several educated posters have stated the same.

[transmitterdan]

Originally Posted by kmacdonald

Of course the total energy stored in a battery over its useful life is a constant. It's not a function of DOD. Several educated posters have stated the same.

I think you are saying the total energy that can be stored and released is a constant and that determines the life expectancy of a battery.

It would seem easy to prove this hypothesis is not correct. If it were then a batter fully charged and never discharged will last forever. I'm pretty sure that isn't true.

[kmacdonald]

The link to the Trojan Chart I posted earlier shows the characteristics of the T-105RE battery. Although I have not verified the accuracy of the chart, I have no reason to dispute it's accuracy.

[kmacdonald]

Originally Posted by transmitterdan

I think you are saying the total energy that can be stored and released is a constant and that determines the life expectancy of a battery.

It would seem easy to prove this hypothesis is not correct. If it were then a batter fully charged and never discharged will last forever. I'm pretty sure that isn't true.

Yes, that is what the Trojan Chart tells us, within it's limits of course. Again, I have not verified the accuracy of the Trojan Chart but I am not going to dispute it without hard evidence.

[StuM]

Originally Posted by kmacdonald

Of course the total energy stored in a battery over its useful life is a constant. It's not a function of DOD. Several educated posters have stated the same.

That's one of your more ludicrous statements.

The total energy which can be stored in a battery and used over its useful life is extremely variable and controlled by multiple factors including ( to name just a few factors):

Average rate of discharge.
How much time it sits at a PSOC
Ambient temperature it operates in.
The charging regime.

That's why some batteries last for many years of sustained use and others of the same make and model are killed within a year.