Depth of Discharge Myth?

[sailorboy1]

Originally Posted by Dockhead

I wonder what Trojan would say about this? They of all people must know the answer. I am unfortunately in a remote place with no easy telephone access, or I would just call them up.

You have internet, post it to them in their technical questions section.

[Dockhead]

Originally Posted by sailorboy1

I think the answer from Trojan is going to be:

If you fully recharge after each cycle, depth of discharge per cycle doesn't matter to the total lifetime amount of power you can remove from the batteries.

But if you don't fully recharge after each cycle the sulfication remaining from each cycle will shorten the life cycle and you will get less total power out the battery.

So the depth discharge effects the amount of sulfication and greater depth result in more damage to the battery.

But, this of course is just my myth theory :-)

That sounds right to me, but I haven't seen a single shred of data to back it up!


Do people just believe it because it sounds right, or has some actual investigation been done, into this alleged mechanism?

[Dockhead]

Originally Posted by sailorboy1

You have internet, post it to them in their technical questions section.

OK, that's a good suggestion. I will.

[daletournier]

Maybe reframing the question is the way to go.

Does anyone fulltime cruising discharge 50% or more regularly/constantly ? If so how many years are you getting out of your bank?

The problem of course is all the variables, due to the fact we dont cruise in a lab. But thats the problem with the ops question, variables, real world stuff.

We read cruisers forum and all come away experts..lol. The thing is theory and practice dont always match.

Here i am following correct charging parameters religiously , then i come across Jim ,the guy on the next boat (right now). Same batteries , same size bank , no solar . He runs the generator twice a day, an hour in the morning and and hour in the evening. Absoption voltage 14.2v ,and dosent worry about an amp counter. His batteries never ever get back to 100%, they are permanently in a PSOC, he tried equalizing once and distorted the cases permanently, dosent do that anymore, YET hes up to his eighth year on this bank! and hes not a power nazi. Go figure.

[a64pilot]

Originally Posted by sailorboy1

I think the answer from Trojan is going to be:

If you fully recharge after each cycle, depth of discharge per cycle doesn't matter to the total lifetime amount of power you can remove from the batteries.

But if you don't fully recharge after each cycle the sulfication remaining from each cycle will shorten the life cycle and you will get less total power out the battery.

So the depth discharge effects the amount of sulfication and greater depth result in more damage to the battery.

But, this of course is just my myth theory :-)

I agree and said just this thing at least once in the thread and was ignored.
He wants a simple answer, well the simple answer is most don’t fully recharge their banks anyway, even if they only discharge 26% or so, for evidence of this everyone raise your hands who says your fully recharged by noon on Solar.

Now take this same guy, let him discharge down to only 25% remaining, he has no chance of fully recharging, unless he hits the dock and has a good charger and stay plugged in overnight. Almost certainly his charger will trip to float way too early and he will finish charging at float voltages, and that can take days, but does happen, there is charge at float voltage.
Sulphation is what kills them early, sulphation comes from short cycling, deep discharges almost guarantee short cycling.

The lab results come from complete 100% recharging each discharge, and if that charge takes 12 hours so what, they don’t define a cycle until completely full recharged.

[a64pilot]

Just for the heck of it, try it one time as a controlled experiment, discharge down to 25% SOC remaining, then kick in the Charger when tied to the dock, but hold it in absorption voltage if you can, often you can set absorption and float to the same voltage, if not you can usually set Absorption .1V higher and float at absorption voltage, or .1 V lower
See how long it takes to get to fully charged, then realize that is how many hours every day you have to run your generator. I bet it’s eight hours or longer.

That is when Lithium shines, cause you can likely get by with running the generator if it’s big enough and you have big chargers for an hour, maybe two.

[a64pilot]

So you can go much deeper that 50% with lead, just it’s the extended recharge time that doesn’t happen usually for people that do, so they are seriously undercharging, and it’s sulphation that build up from undercharging that kills the batteries in real life.
You don’t see that in the Lab, cause well they are battery experts, they wouldn’t undercharge, every charge they do is just right.

[ramblinrod]

Originally Posted by Dockhead

This is turning into a really interesting discussion.



Some people say that although you can't see it in the cycle life charts, there is an objective reason why you are disproportionately shortening the life of your batteries if you discharge them regularly below 50%, and you shouldn't do it.


Other people say: It's a myth; there is no downside to using more of the batteries' capacity.




Where is the truth in this? And on the basis of what facts and data? Fascinating. I have no idea what the right answer is.

I wonder what Trojan would say about this? They of all people must know the answer. I am unfortunately in a remote place with no easy telephone access, or I would just call them up.

Ya know, ya really don't have to live up to your handle.

If you wish to continue to ignore the correct answers you have been given here, I recommend you contact the manufacturer, using the same technology and equipment you are using to post here.

Else, let me try to one last time to be more clear:

The concept of improved battery life by not discharging too deeply is not a myth.

Technical reasons why?

1. Lab cycle charts don't represent real life.

Real life hurts batteries more, the deeper they are discharged.

A 10,000 A-hr bank that only gets discharged 2% doesn't make a lot sense on a boat due to weight and space, and the slower the discharge rate, the longer the battery is held at PSOC, and the more the battery is hurt, so the general rule of thumb is ~ 50% DOD is best for FLA.

2. Lab cycles vs A-hrs doesn't tell the story about the amount of life energy transfer realized. Look at lab cycles vs W-hrs at various depth of discharge and you will see a different story that favours less DOD. This still can only be considered with a grain of salt as lab cycles are virtually meaningless in the real world.

3. At low SOC, the risk of extended PSOC at a deeper DOD is greater, and does more harm to battery real world life.

If you cannot accept this, and need more in depth precise data, and are not getting the answers you seek, why not stop chastising others and perform the tests yourself if you feel this is so important?

Maybe when you see first hand what others are trying to explain to you, you will understand.

Here's a test protocol that should give you what you are asking for:

1. Set up 10 equal house banks on your personal vessel.

2. Automatically alternate the connection of each bank to normal loads until it reaches the target DOD (0-100% in 10% increments per bank).

3. When the target DOD is reached, recharge for say 2 hours of ICE running, or some combination of lesser ICE and solar or wind. You may not always get back to 100% before starting the discharge cycle again, especially on the deeper discharged banks.

4. When the 10% DOD bank finally reaches 80% of original capacity, and the test is complete, repeat this test 10-20 times and average to eliminate influence of anomalies.

Please report your results and conclusions here.

[Dockhead]

Originally Posted by a64pilot

I agree and said just this thing at least once in the thread and was ignored.
He wants a simple answer, well the simple answer is most don’t fully recharge their banks anyway, even if they only discharge 26% or so, for evidence of this everyone raise your hands who says your fully recharged by noon on Solar.

Now take this same guy, let him discharge down to only 25% remaining, he has no chance of fully recharging, unless he hits the dock and has a good charger and stay plugged in overnight. Almost certainly his charger will trip to float way too early and he will finish charging at float voltages, and that can take days, but does happen, there is charge at float voltage.
Sulphation is what kills them early, sulphation comes from short cycling, deep discharges almost guarantee short cycling.

The lab results come from complete 100% recharging each discharge, and if that charge takes 12 hours so what, they don’t be fine a cycle until completely full recharged.

No, you misunderstand -- I don't want a simple answer, I want technical facts which confirm this explanation (or some other; or which disprove it).


I agree with all of you that this sounds plausible. I guess it's probably true, but I would love to know why and to what extent, in facts!


EDIT: Actually, there is something like a theory, in this post. You are saying, if I understand you right, that



1. "Sulphation comes from short cycling" -- I.e., charging the batteries without finishing. So is that right? Does sulphation come from cycling to less than a full charge? Or from time you hold them at partial SOC? This is important.



2. "The average user will leave the battery more discharged, for longer, if he's cycling deeper -- ergo, more sulphation". OK, but what if he cycles deeper but charges higher since he's doing it less often? What then? We don't know if we don't understand the mechanism of sulphation, and I don't, and it doesn't seem to me that any of us does.

[Dockhead]

Originally Posted by ramblinrod

. .. If you wish to continue to ignore the correct answers you have been given here, I recommend you contact the manufacturer, using the same technology and equipment you are using to post here.

I have not ignored anything -- and a lot of the information which has been posted by you and others has been interesting and useful, for which I am grateful. However, there is no answer to my question in any of this information!

Originally Posted by ramblinrod

Else, let me try to one last time to be more clear:

The concept of improved battery life by not discharging too deeply is not a myth.

Technical reasons why?

1. Lab cycle charts don't represent real life.

Real life hurts batteries more, the deeper they are discharged.

Those are not "technical reasons why; those are bare assertions without any facts or even any explanation. I have no reason to doubt that this is true, and as I said, it sounds right to me. But I want to know why (and that also means WHY others on here, who say otherwise, are wrong). I don't demand this answer from you or anyone; but if anyone even has a good guess -- I'm keenly linterested, and that's all I'm saying.

Originally Posted by ramblinrod

2. Lab cycles vs A-hrs doesn't tell the story about the amount of life energy transfer realized. Look at lab cycles vs W-hrs at various depth of discharge and you will see a different story that favours less DOD. This still can only be considered with a grain of salt as lab cycles are virtually meaningless in the real world.

This is a good point, which I noted the first time you made it. But they DO tell the story if you just correct for voltage. And this point only accounts for a relatively small change in what the cycle life charts mean in terms of kWH handled vs. lifetime.

Originally Posted by ramblinrod

3. At low SOC, the risk of extended PSOC at a deeper DOD is greater, and does more harm to battery real world life.

Sounds right, but why? There is not even any theory here, about why. I'm not chastising anyone; there's no shame in not knowing (I sure don't know myself). I'm merely asking if anyone knows.




And to that end, I just wrote a long letter to Trojan tech support. I'll post what they answer. I'm pretty sure I'm not the only person who is interested in this question. And where the heck is MaineSail?

[Paul L]

Originally Posted by newhaul

ok lets see 4 years or 10 years 10÷4= 2.5 changes of Fla per Lfp
Now the charge rate of 1C from 20% to 95% saves on fuel. Also half the ah needed to do the same job.
2.5 years and 10 years. For the deeper cycling 10÷2.5 = 4 changes for Fla vs 1 for Lfp
Still have the much higher charge rate so saves many hours running dino juice.
99% likely to reach full on solar alone if fitted. Daily vs Fla.
And no more having to remember watering them
So worth thinking about at next battery change.

Lithium has lots of nice features. But these are benefits over its lifetime, not direct dollars comparison. Decent golf cart batteries are drop in and cheap. Lithium is not drop and the setup is either expensive or time consuming, or both.

[a64pilot]

By facts I guess you mean published data?
I do think a call to a manufacturer is in order, in particular a Gentleman at Lifeline who was really the brains behind that outfit, he is older now and doesn’t hear as well, prefers to email now, trying to remember his name, but skip rings a bell.
I have only called there once or twice, once I called specifically to talk to Justin Goodbar I think his name was, his name was given to me by our sales contact for Concorde batteries, we had a decent technical conversation.
Then I called the help desk once, and well frankly You could tell he wasn’t really enthused and was used to answering stupid questions. You know the continuing to argue, the green light is on, I must be charged types of questions.

I think however if you call Engineering dept and state I’m outfitting an expedition vessel and would like to talk to an Engineer about depth of discharge strategies, you may get past the guy who’s job Is mostly to convince people that yes, batteries are like your little dog, they need a drink once in a while too.

[newhaul]

Originally Posted by Paul L

Lithium has lots of nice features. But these are benefits over its lifetime, not direct dollars comparison. Decent golf cart batteries are drop in and cheap. Lithium is not drop and the setup is either expensive or time consuming, or both.

the bank I just got is basically drop in I just adjusted my solar to stop charging .2 volt below the banks max charge point . ( Lfp actually don't like to be charged to 100% ) Not to hard to do . Heck you should adjust the charge controller for each different manufacturers specs for their Gc2 Fla battery as well to maximise its life expectancy.

[sailorboy1]

I doubt there’s going to be experimental data of cycles for not recharging afterwards. That’s really “I’m a cruiser and my batteries lasted 4.3 years.”

[Dockhead]

Originally Posted by a64pilot

By facts I guess you mean published data?
I do think a call to a manufacturer is in order, in particular a Gentleman at Lifeline who was really the brains behind that outfit, he is older now and doesn’t hear as well, prefers to email now, trying to remember his name, but skip rings a bell.
I have only called there once or twice, once I called specifically to talk to Justin Goodbar I think his name was, his name was given to me by our sales contact for Concorde batteries, we had a decent technical conversation.
Then I called the help desk once, and well frankly You could tell he wasn’t really enthused and was used to answering stupid questions. You know the continuing to argue, the green light is on, I must be charged types of questions.

I think however if you call Engineering dept and state I’m outfitting an expedition vessel and would like to talk to an Engineer about depth of discharge strategies, you may get past the guy who’s job Is mostly to convince people that yes, batteries are like your little dog, they need a drink once in a while too.

Not necessarily something published -- hell, any kind of fact. Even a decent theory would be interesting.


Thanks very much for the contact -- I'll write to this guy with the same question I sent Trojan.