Depth of Discharge Myth?

[newhaul]

Originally Posted by ramblinrod

As I understand it LFP is more tolerant of PSOC (not
normally an issue if one has adequate wind and solar) but far less tolerant of
over or undercharge, like kill the bank if ever done.

There are few batteries more tolerant to abuse and misuse than FLA. If you think LFP is an install it and forget about it solution, you gotta whole nuther thing comin’.

33 years? More like 3.3 months, if yer lucky.

PS most of the cells I see are rated 2000 cycles at .3C to 20% DOD and have charge limits of 1C.

For real world cycles, I would be 1/2 that, if one is really trying to use 80% of capacity on a regular basis.

ok you seem to have a poor opinion of Lfp batteries please inform us
( as we are all still learning ) what experience you base your Lfp battery life expectancy statements on.

[john61ct]

Originally Posted by evm1024

100% full is a nice phrase but in reality what do you call 100% full?

No, it is objective, endAmps. Any decent battery the maker will give the precise spec for that model..

Otherwise by default, .005C

Or trailing amps does not decline more than .1A for over an hour, useful as a bank ages.

[Dockhead]

Originally Posted by ramblinrod

Sounds like your boat is no where near “the average 35 ft +/- cruising sailboat.

Most of those have full canvas, 20 year old Dacron sails, and maybe a little Honda 2000.

For your specific case, after thorough electrical review, I may recommend LFP and no solar or wind. There’s a good chance I would work with you to get you over the solar and wind phobia / distaste, but if I couldn’t then maybe, just maybe LFP makes sense for you.

Ha, ha, ha!


This is a good post I must say, I underestimated your sense of humor.




Just note that the phobia is NOT indeed to solar. I had solar on the last boat and loved it. Solar is great. The phobia is to WINDAGE.



If you can invent a zero windage solar system which would work on my boat, I would pay you good money.


Actually there are zero windage solar systems -- I've seen them let into the pilothouse roofs of custom metal boats built in the yard in the Netherlands where I hope to have my next boat built. But this boat doesn't have pilothouse, bimini, or any other place for such a system. So I'll just have to live with IC charging for the time being.

[newhaul]

Originally Posted by ramblinrod

As I understand it LFP is more tolerant of PSOC (not
normally an issue if one has adequate wind and solar) but far less tolerant of
over or undercharge, like kill the bank if ever done.

There are few batteries more tolerant to abuse and misuse than FLA. If you think LFP is an install it and forget about it solution, you gotta whole nuther thing comin’.

33 years? More like 3.3 months, if yer lucky.

PS most of the cells I see are rated 2000 cycles at .3C to 20% DOD and have charge limits of 1C.

For real world cycles, I would be 1/2 that, if one is really trying to use 80% of capacity on a regular basis.

question where did you get the .3C discharge and max of 1C charging.
The cells I am considering have a 1C charge and discharge rate.
With burst to 3C discharges.
With a cycle rating of 7500 with an 80% DOD and a 10 year warranty

[john61ct]

Originally Posted by ramblinrod

As I understand it LFP is more tolerant of PSOC

No, there is no such issue at all. Being full is unhealthy, it prefers sitting long periods depleted

< not normally an issue if one has adequate wind and solar

Tautology, and a huge issue with most boat, especially those without convenient ICE charging on demand.

LFP ratings are gross underestimates based on too-high charge rates.

Even with drawing down 80% DoD.

[Dockhead]

Originally Posted by ramblinrod

PS most of the cells I see are rated 2000 cycles at .3C to 20% DOD and have charge limits of 1C.

For real world cycles, I would be 1/2 that, if one is really trying to use 80% of capacity on a regular basis.

I would like to know what LiFePo4 cells you've seen, which are rated like that. None that I've seen. I believe you have mistaken DOD for percentage charge.



Winston -- the most popular ones here, and the ones Victron use in their lithium systems, are rated 3000 cycles at 80% DOD, and 8000 at 55%. MaineSail's (and other) testing suggest that these ratings are very conservative.


And that's very different from lead-acid batteries, which give not more, but far less cycle life than their ratings, if used in any kind of PSOC regime. Typically a few hundred cycles, which is fine for boats which spend 90% of the time in marinas, but much less good for those used much off grid.

[newhaul]

Originally Posted by newhaul

question where did you get the .3C discharge and max of 1C charging.
The cells I am considering have a 1C charge and discharge rate.
With burst to 3C discharges.
With a cycle rating of 7500 with an 80% DOD and a 10 year warranty

I just checked the specs and I must make a correction they are rated for a 5C maximum charge rate with a 10C discharge rate.
And a standard charge rate of .5C which for my installation initially will be 50 amps ( initial testing will be 100ah bank 4s4p .

[evm1024]

Originally Posted by ramblinrod

Incorrect,

The reason for the 400 A-hr FLA to 200 A-hr LFP was due to many people claiming that the full capacity of LFP is usable whereas only 50% of FLA is usable, and suggesting that the LFP bank could be half the FLA bank size, thereby attempting to justify the cost difference.

I responded explaining that the 50-20% SOC range of
FLA can be used occasionally if recharged rapidly and therefore could
Be considered occasional use reserve capacity, thereby making 80% usable, just not very frequently.

For a proper comparison of LFP one has to also have reserve capacity available for use.

Therefore to compare apples to apples the two banks must be the same size.

My example using a half sized LFP bank, was to demonstrate that principle of what would happen if a half sized LFP bank (no reserve capacity) was selected.

Thank you for acknowledging that reserve capacity is needed when switching from FLA to LFP and the banks should be approximately equal sized.

Finally, one small element of common opinion.

I'm confused here (What else is new?)

So were you trying to prove that half sized LiFePO4 banks could not compete with full size FLA banks.

Or were you trying to show that each bank be it FLA or LiFePO4 needed a reserve capacity?

Or were you trying to show that FLA was "better" than FLA?

Wait!

That thread was called LiFePO4 vs FLA - The Real Deal so clearly you were contrasting FLA to LiFePO4.

No Wait!

Now I'm really confused you said Shouldn't we design for 50% reserve capacity? and then went ahead and spec'ed a half sized LiFePO4 bank.

And the list goes on.


Really let's do apples to apples. (and remember that this thread is about depth of discharge)

[evm1024]

Originally Posted by ramblinrod

Incorrect,

The reason for the 400 A-hr FLA to 200 A-hr LFP was due to many people claiming that the full capacity of LFP is usable whereas only 50% of FLA is usable, and suggesting that the LFP bank could be half the FLA bank size, thereby attempting to justify the cost difference.

I responded explaining that the 50-20% SOC range of
FLA can be used occasionally if recharged rapidly and therefore could
Be considered occasional use reserve capacity, thereby making 80% usable, just not very frequently.

For a proper comparison of LFP one has to also have reserve capacity available for use.

Therefore to compare apples to apples the two banks must be the same size.

My example using a half sized LFP bank, was to demonstrate that principle of what would happen if a half sized LFP bank (no reserve capacity) was selected.

Thank you for acknowledging that reserve capacity is needed when switching from FLA to LFP and the banks should be approximately equal sized.

Finally, one small element of common opinion.

But completely ignored that the occasional use of the capacity below 50% (or some other number) in FLA was a major factor in reducing the life of said bank by up to or more than a factor of 10.

This is especially true in typical cruising boats that I see.

In order to avoid this loss of capacity they need to be fully charged ASAP and there is very often no chance of reaching 100%SOC with solar alone. Thus they become slaves to ICE charging.

[fxykty]

Originally Posted by Dockhead

Ha, ha, ha!


This is a good post I must say, I underestimated your sense of humor.




Just note that the phobia is NOT indeed to solar. I had solar on the last boat and loved it. Solar is great. The phobia is to WINDAGE.



If you can invent a zero windage solar system which would work on my boat, I would pay you good money.


Actually there are zero windage solar systems -- I've seen them let into the pilothouse roofs of custom metal boats built in the yard in the Netherlands where I hope to have my next boat built. But this boat doesn't have pilothouse, bimini, or any other place for such a system. So I'll just have to live with IC charging for the time being.

Many semi-flexible panels can be walked on. Does a large Oyster seriously have no flat-ish areas such as cabin top where you could mount panels and wouldn’t be walking on them much? If you take Solbian SP or SXp as an example, they’re 3mm thick, can be glued or mechanically fastened, and are as efficient as glass panels at a fraction of the weight. Would that not be close enough to zero windage?

[ramblinrod]

Originally Posted by newhaul

ok you seem to have a poor opinion of Lfp batteries please inform us
( as we are all still learning ) what experience you base your Lfp battery life expectancy statements on.

We are all still learning as it is a relatively new application for a relatively new technology.

Like many marine electrical professionals my personal experience is limited, so I have to rely on the experience of those I feel I can trust. Of the ones I trust, most agree that if you overcharge or undercharge LFPs without very high risk of irreparable damage.

Again, one does not have to have personal experience nor be able to cite published references to know something.

I have never personally wrestled an alligator.

Nonetheless I “know” I don’t want any in my pool. ;-)


(Actually, I don’t own a pool any more. What time I can manage to get away from making customer boats awesome, I spend on my own boat, swinging on anchor, charging my 6 year old (mostly) FLA bank fully, almost solely with solar.

[ramblinrod]

Originally Posted by newhaul

ok you seem to have a poor opinion of Lfp batteries please inform us
( as we are all still learning ) what experience you base your Lfp battery life expectancy statements on.

Originally Posted by evm1024

I'm confused here (What else is new?)

So were you trying to prove that half sized LiFePO4 banks could not compete with full size FLA banks.

Or were you trying to show that each bank be it FLA or LiFePO4 needed a reserve capacity?

Or were you trying to show that FLA was "better" than FLA?

Wait!

That thread was called LiFePO4 vs FLA - The Real Deal so clearly you were contrasting FLA to LiFePO4.

No Wait!

Now I'm really confused you said Shouldn't we design for 50% reserve capacity? and then went ahead and spec'ed a half sized LiFePO4 bank.

And the list goes on.


Really let's do apples to apples. (and remember that this thread is about depth of discharge)

I am sorry if you are confused.

I’ve tried to be as clear as I can be.

Position Summary

1. Before making modifications to a marine electrical system, one should perform an electrical energy needs analysis.

2. The Marine electrical system needs to be balanced, considering, energy demand, storage capacity and charging capacity.

3. The marketing “features” of any product or technology need to be evaluated to determine if they will actually result in “benefits” for the user in a real world setting.

4. I normally try to design a system that represents “best value” for the customer.

5. After the energy analysis performed to date, I have yet to encounter one (personally) where LFP represented a superior solution (all factors considered) to FLA.

I have never stated that LFP can’t be a better solution. Just in all the cases I have personally reviewed, including boats being outfitted for full time cruising, including my own personal vessel.

I scrutinize all reports of FLA and LFP experiences.

Often, I find those attributing improved performance due to switching to LFP, when in fact, some if not all improvement was due to simultaneous:

1. Storage capacity increase.
2. Charging capacity increase.
3. Improved maintenance and monitoring.
4. Attempts to justify unwarranted costs.

My first encounter with Li on a cruising sailboat was about 5 years ago. The owner initially claimed they were fantastic. After a few probing questions, he acknowledged that they were expensive, difficult to implement, fraught with problems, and he wouldn’t actually recommend them to others.

I certainly understand that as they become more mainstream, these factors will likely all be improved. Are we their yet. Not in my opinion. YMMV.

[wsmurdoch]

Originally Posted by evm1024

100% full is a nice phrase but in reality what do you call 100% full?

It it where the specific gravity reached some value? Is it when the amps in do not give any greater return? What would be 100% full? Is it when the capacity is greater than the spec'ed number?

Perhaps it should be the point where there is no damage to the cells due to PSOC.

In the previously linked article "Charging Algorithms for Increasing Lead Acid Battery Cycle Life for Electric Vehicles" fully charged seems to be indicated by ZDV... "

"The battery was then charged with 10 amps until ZDV was reached. During the ZDV charging, the battery voltage was sampled once every second for 30 seconds. The 30 readings were then averaged, and the average was subtracted from the previous 30-second average and then compared to a limit. The limit for this particular test was 15 mV. The limit chosen depends on the number of cycles placed on the battery. The 15-mV limit was used through cycle 295 and then lowered to below 10 mV after cycle 295. The final test for ZDV is when the limit is not exceeded 5 consecutive times. In other words, the difference between successive 30-second average readings needs to be below the assigned limit five consecutive times."

I found that measure quite interesting because it is a measure that could be used by a battery SOC monitor that can only measure the voltage at the battery (SmartGauge). It is also a measure that can be used on a lead acid battery that is under charge as opposed to resting for several hours before measuring a resting voltage.

The battery is charged when the voltage has been rising (a charging device is operating at a rate greater than the load) and the voltage rise per unit time gradually declines to a near zero amount.

Bill Murdoch

[evm1024]

Originally Posted by ramblinrod

I am sorry if you are confused.

I’ve tried to be as clear as I can be.

Position Summary

1. Before making modifications to a marine electrical system, one should perform an electrical energy needs analysis.

2. The Marine electrical system needs to be balanced, considering, energy demand, storage capacity and charging capacity.

3. The marketing “features” of any product or technology need to be evaluated to determine if they will actually result in “benefits” for the user in a real world setting.

4. I normally try to design a system that represents “best value” for the customer.

5. After the energy analysis performed to date, I have yet to encounter one (personally) where LFP represented a superior solution (all factors considered) to FLA.

I have never stated that LFP can’t be a better solution. Just in all the cases I have personally reviewed, including boats being outfitted for full time cruising, including my own personal vessel.

I scrutinize all reports of FLA and LFP experiences.

Often, I find those attributing improved performance due to switching to LFP, when in fact, some if not all improvement was due to simultaneous:

1. Storage capacity increase.
2. Charging capacity increase.
3. Improved maintenance and monitoring.
4. Attempts to justify unwarranted costs.

My first encounter with Li on a cruising sailboat was about 5 years ago. The owner initially claimed they were fantastic. After a few probing questions, he acknowledged that they were expensive, difficult to implement, fraught with problems, and he wouldn’t actually recommend them to others.

I certainly understand that as they become more mainstream, these factors will likely all be improved. Are we their yet. Not in my opinion. YMMV.

Thanks for the description of Sheen Marine's sales philosophy.

However this and the other thread are technical discussions of the merits and drawbacks of FLA, LiFePO4 batteries and specifically How depth of discharge effects the cycle count and thus lifespan of FLA batteries.

Now of a few questions.

Hey Rod,

How much battery capacity do you have on your boat? Also, How much solar, wind and ICE charging capacity do you have. Also, what loads do you commonly have.

I've almost got my model up and running and I think it would be interesting to take a well thought system like yours and plug the numbers into the model to see if the results get even close to what you see.

I'll be able to take your real-world numbers and make changes to the model to get closer to the real-world.

Thanks!

[ranger58sb]

Originally Posted by ramblinrod

Of the ones I trust, most agree that if you overcharge or undercharge LFPs without very high risk of irreparable damage.

????

-Chris