Depth of Discharge Myth?

[evm1024]

I stumbled onto another paper that may be a useful read. Chapter 1 is the most apropos in that it gives a great summary of what we know about lead acid batteries. If nothing else reading it would give the reader an in-depth background of whet we know about lead acid batteries.

Other chapters head off into the meat of the thesis and may have less interest to the lay reader.

https://tel.archives-ouvertes.fr/tel-00443615/document

[newhaul]

Originally Posted by ramblinrod

I think it goes without saying that I recommend you read and comprehend what I post.



I wish I could say it was in "The Bible" because that would be easy.

But I doubt it was there.

So it could be a result of any number of articles I have read, tests I've performed, or conditions I have experienced, over my lifetime.

I am not about to waste my time trying to cite everything or anything because you want it. I know it. If you need something more than my say so, it is your responsibility to find it not mine. Again, try Google.



No, I would not.

I have provided you with some information that I hoped would help.

Though I believe it should have, you have declared it has not, as apparently it does not meet your standard of irrefutability.

If you wish to ignore what I post because of this, that's OK. Your loss.

If you wish to research and verify what I post, have at it.

If you don't, that's fine to.

The onus is not on me to prove what I know to you, because I offered some friendly advice on a forum as a kind gesture.

IOW you don't really understand it either .
I admit I don't understand it as well as I suppose I should.

[Dockhead]

I was on passage for four days and this thread sure went downhill!


Could we keep it civil, please?


I appreciate Rod's comments, but he has misunderstood people's reaction to them. What he has written ("sulfation is a function of DOD and time left that way" or whatever) is a good formulation of the popular explanation of what happens, but the popular, simplified explanation is not at all satisfying to the several people on here who want to go deeper than that. That's no insult to Rod. It's just that every single person in this thread knows that already, and it doesn't answer the question. References to Nigel Calder, whom I guess every single person in this thread has read, also don't help. It's not that we don't believe you, Rod! No need to be offended! It's that you haven't answered the question; you've just given us the same simplistic explanation we've been hearing since we were kids. And that's fine; probably all most people ever need.


But those of us who want more have to dig deeper. I was on the ocean for four days, but now I have a connection again so I'll get back to my reading and I'll share anything new I find out. I hope some of the rest of you will come up with something as well.



So for those who are curious -- let's keep digging. For those who aren't -- there are plenty of other threads on CF to keep you entertained!

[john61ct]

Perhaps a new thread

WHY - scientifically - does deep discharge shorten lifespan?

will attract those interested in such research.

This thread's title implies skepticism that it does, so is likely being skipped by the vast majority already certain that it is no myth.

[poiu]

There is an assumption in many of the postings here that all lead acid batteries behave the same way. They don't.


There is one type of lead acid battery that will perform much better than the usual Trojan type and that is a traction or fork lift truck battery. They are often made of 2v cells and are made for very deep discharges. A fork lift truck will work for hours non stop, discharging its battery to 70% or more usually 80%, then will roll the battery out, slot another in and carry on working, often round the clock and with several battery changes per day. A battery will last 1500 deep cycles, so incomparably better than a typical boat battery.


If you want the longest life and probably the best value for money and you don't want lithium then get traction batteries.

[newhaul]

Originally Posted by poiu

There is an assumption in many of the postings here that all lead acid batteries behave the same way. They don't.


There is one type of lead acid battery that will perform much better than the usual Trojan type and that is a traction or fork lift truck battery. They are often made of 2v cells and are made for very deep discharges. A fork lift truck will work for hours non stop, discharging its battery to 70% or more usually 80%, then will roll the battery out, slot another in and carry on working, often round the clock and with several battery changes per day. A battery will last 1500 deep cycles, so incomparably better than a typical boat battery.


If you want the longest life and probably the best value for money and you don't want lithium then get traction batteries.

sounds great till you look at the average of a pound per ah when built into 12v banks great lifecycles but dang.

[sailorboy1]

I think a quick web search will tell you the death mechanism of batteries so I’m not typed it with one finger on my iPad

[john61ct]

They still last many times more cycles if not cycled so deeply.

And most are too heavy.

Fundamentally this specific issue is similar with all lead, even Firefly Oasis.

It's just that some types start off more robust than others, or the curve of the chart may be a slightly different slope.

[Dockhead]

Originally Posted by john61ct

Perhaps a new thread

WHY - scientifically - does deep discharge shorten lifespan?

will attract those interested in such research.

This thread's title implies skepticism that it does, so is likely being skipped by the vast majority already certain that it is no myth.

Why a new thread? That's exactly what this one is about.

[poiu]

Originally Posted by john61ct

They still last many times more cycles if not cycled so deeply.

Fundamentally this specific issue is similar with all lead, even Firefly Oasis.

It's just that some types start off more robust than others, or the curve of the chart may be a slightly different slope.

It is not the same. They are designed for deeper discharge and the relative loss of life from going to 80% is hugely less with traction batteries compared to leisure batteries. The curve is a totally different shape.

[a64pilot]

Originally Posted by sailorboy1

I think a quick web search will tell you the death mechanism of batteries so I’m not typed it with one finger on my iPad

That and or call a reputable battery manufacturer that has a real help desk.
Call Lifeline and ask to speak with one of the Godbers or their Engineering dept.

Problem with the Internet is that there is so much bogus, purely unsubstantiated “truths” out there by “experts” in the field, and these experts for some reason have their own fan boys and you see the same “facts” being posted over and over until some begin to believe it.
Even some are well meaning and test, their testing methodology is often flawed, well meaning, but flawed.

However when you find papers written by the Sandia National Labs or DARPA etc., pay attention.

[Maine Sail]

Originally Posted by Dockhead

What am I missing??!!

What you're missing is what happens to batteries in the real world outside of an extrapolated table created from white-glove lab data.

Routinely dipping to 80% DOD on lead acid, other than GEL (they actually handle this marginally well), in the real world is just not good for the batteries. I see this repeatedly in actual capacity testing of used marine batteries.

This is not to say never dip to 80% DOD. The occasional dip to 80% DOD is fine, and can even be somewhat healthy, provided you recharge ASAP to 100% SOC immediately there after.

Going to 80% DOD routinely, in my experience, (based on actual testing) just does not result in the energy throughput the curve depicts, not even close. Why? We're not operating our banks in a laboratory. One can assume this is why nearly every LA battery maker, including Trojan, Lifeline, East Penn etc. suggest 50% DOD max. It's because I suspect they do actually know what happens outside the lab. A bottom DOD of 50% helps minimize impact on reputation I suppose..

Lifeline initially marketed their batteries for 80% DOD and it left a bad taste for many AGM early adopters. Lifeline has since revised their suggested DOD to 50% max. A result of real world use vs. lab data.??

I was on a transient boat at the end of July for an "engine issue" (plugged 2 micron primary). The owner had "motored all day", a 52nm run with no wind or wind on the nose, before the engine slowed repeatedly then died altogether. He was able to limp in under sail..

During the bleeding process the bank died on the second start attempt (one bank no other bank on-board). When I looked at the date code on the G-31 batteries they were dated March of 2018 or basically brand spankin' new.

When I asked the owner how they had been performing he said they were great in April, May and June but now they were "really bad". After a few questions he explained to me that his normal "it's time to recharge" voltage was approx 11.6V.

The batteries were so destroyed, in just a couple months, that even when at a 10.67V open circuit voltage, after the starting attempts, when we got them jumped the voltage immediately jumped up to 14.2V from a 0% SOC voltage reading, with only a 60A alternator. This is completely bypassing the bulk charge stage due to sulfation. This had been his third jump-start of the trip and he assumed it was bad cables or connections.

This behavior is due to sulfation and no matter how long he charged the bank it was just done. Even after a rather aggressive EQ process the two batteries sagged to 11.2V under a measly 10A load the next morning.

Two destroyed West Marine / East Penn G-31 batteries in just a few months. He simply shrugged and said "I'm going to return them to West Marine, these batteries suck." This was not the fault of West Marine or the battery maker but rather due to overly deep cycling on a cruising boat without attaining 100% SOC often enough.

In contrast I have customers who shallow cycle, charge properly and who get 10+ years out of deep-cycle LA batteries and a few GEL banks that have gone over 15 years.

All I can say, and it's not my money I am trying to save here its yours, is don't routinely deep-cycle to 80% DOD unless you have batteries such as a quality GEL, Firefly, or others that are specifically designed for it. Testing of real world marine use batteries shows me the cycle life graphs are simply not translatable to the real world in terms of the energy throughput they suggest.

[Delfin]

Originally Posted by sailorboy1

the real question is what you they consider a cycle and whether that has much in common to real life use

But I don't see how lithium will ever become as cost effect as golf cart batteries except on a lab spreadsheet. If they were don't you think golf courses would start using them. I got 5 years out the last set and abused them, so they cost me $0.25/day. I probably spill more beer a day than that.

They do use them.

http://www.stephentucker.net/daily-grind/lithium-ion-golf-carts-now-worth/

[Dockhead]

OK, for those of you who are interested in the actual physics and not just the Wikipedia-level explanation of lead acid battery sulfation, I think I am closing in on the actual science.


Most of the hard science has been published in the Journal of Power Sources. Unfortunately JPS does not provide access to older articles through the paid subscription services like ResearchGate and DeepDyve, the two I use, but you can request the authors to give access, which I've done for a few of these.


Some of the basic sources:


GIBSON, I. and K. PETERS (1982) “Sulphation in discharged lead-acid batteries,”Journal of Power Sources, 8(2)


Takeuchia T., Sawai K., Tsuboia Y., Shiota M., Ishimotoa S., Hirai N., Osumia S.: The partial state-of-charge cycle performance of lead-acid batteries. J. Power Sources 189, 1190–1198 (2009)


TAKEHARA, Z. (2000) “Dissolution and precipitation reactions of lead sulfate in positive and negative electrodes in lead acid battery,” Journal of Power Sources, 85(1)


There is also a very interesting dissertation available free here:


https://www.mne.psu.edu/mrl/theses/YingShi_dissertation.pdf


Which goes very deeply into the subject of modelling of the "state of health" of lead acid batteries and non-destructively monitoring their failure mechanisms.





What have I learned so far?


Well, first of all, the article someone else cited above, which refers to "sulfation" as a myth or at least a misnomer, is absolutely correct. What we get from Wikipedia is a fairy tale which might roughly approximate some of what goes on, but the reality is far more complex, and there is more than one failure mechanism which we typically lump in as "sulfation".


It is not true at all that "sulfation" is caused by transformation of "amorphous" lead oxide, into crystalline lead oxide. All lead oxide in our batteries is crystalline. The difference is that healthy, reactive lead sulphate has a much finer crystalline structure which has a much greater surface area, allowing it to react readily with the electrolyte in the basic dissolution-precipitation reaction which is the basic power storage and release mechanism of our batteries. What determines, at least to some extent, the difference between healthy, reactive lead sulphate crystals and the crystals present in case of "hard sulfation" is the size of the crystals, which is different by orders of magnitude depending on their origin -- those formed by the basic electro-chemical reaction are small and reactive, and those formed by recrystallization are large and passive. This recrystallization is known as "Ostwald ripening" -- see: https://goldbook.iupac.org/html/O/O04348.html. However, the size of the crystals alone is not the whole story -- there are still other complexities. I haven't read the Gibson article yet because it's not included in any of my subscriptions, but I have requested a copy of it.



So do I now understand how it all works? Heck no! But I start to get a glimmer of understanding -- so if I may speculate a little after reading all this science, a full finishing charge on the batteries gets rid of the lead sulphate and so prevents it from being dissolved and redeposited as larger, harmful, passive crystals via the Ostwald ripening process. So a battery in a partial state of charge, basically, has material available for this harmful process, and a battery which is fully charged, does not.


Some other random things I picked up along the way:


* The scientists basically condemn amp-counting as a method of evaluating state of charge, and they explain why -- the relationship between power input into the battery during charging and state of charge achieved is highly non-linear because of different side reactions which occur at different stages, particularly near full charge. Acid concentration (which we measure as specific gravity) and resting voltage have a highly reliable, linear relationship to each other and are far more reliable measures of state of charge.


* Positive plate corrosion is much more complex than we imagine, and surely accounts for a significant proportion of battery failure cases attributed to "sulfation". The Takeuchi article cited above goes deeply into this. The complexity of this particular reaction can be seen from this diagram from the article:





Unfortunately we don't get a clue about how to operate our batteries to minimize this harmful mechanism -- the article concentrates on different electrode compositions as a way to fight it.




* Another really important failure mechanism is cell imbalance resulting from sometimes even small degradation of the performance of one cell in a battery. This is a kind of feedback loop which turns small damage into big damage.




Someone called LiFePo battery systems as "science experiments" (it may have been me! ). Well, that's almost nothing compared to our lead acid batteries, which are real science experiments, much more complicated than most of us imagine.


I have only really just scratched the surface of this so far, but I'll continue reading and let you know what I figure out. Maybe someone else on here can contribute some understanding as well?

[sailinglegend]

Originally Posted by Dockhead

....So do I now understand how it all works? Heck no! But I start to get a glimmer of understanding -- so if I may speculate a little after reading all this science, a full finishing charge on the batteries gets rid of the lead sulphate and so prevents it from being dissolved and redeposited as larger, harmful, passive crystals via the Ostwald ripening process. So a battery in a partial state of charge, basically, has material available for this harmful process, and a battery which is fully charged, does not....

Look at it this way:

Sulfation is the formation of lead sulfate crystals on the lead plates as a result of the chemical reaction of current discharge.

The basic lead-acid chemical reactions in a sulphuric acid electrolyte are as follows:

PbO2 + Pb + 2H2SO4 = (discharge----><----charge) = 2PbSO4 + 2H2O

Put in more simple English - when the battery is discharged the lead (Pb) and lead oxide (PbO2) and the hydrochloric acid (2H2SO4) convert to lead sulphate crystals (2PbSO4) and water (2H2O) which dilutes the hydrochloric acid and so lowers the specific gravity. During charging the reverse happens and the extra water that was produced during discharge is removed and the Specific gravity of the sulphuric acid returns to its original level. This is why SG can be used to determine when a battery is fully charged.

During charging the reverse happens converting the lead sulfate back to lead and sulphuric acid, but if not fully recharged then any lead sulfate crystals not converted back will harden over a relatively short time and will provide a permanent layer of lead sulphate crystals on the lead plates which will reduce the capacity of the battery.

Simple!