LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

[CatNewBee]

AFAIK, "Sailing Sisu", a 45" Leopard sport-bridge recently launched was outfitted with a Victron Lithium Setup, at least they talked about it, but I am not sure what exact batteries they use.

Sailing Sisu

https://www.youtube.com/watch?v=wDhpkHN_AQY

[john61ct]

NMC is a completely different chemistry from LFP, different charging profile, temperature issues, nowhere near the same lifetime cycles potential. . .

IMO this question is worth its own thread, an extensive discussion would dilute the value of this one.

That said Victron is a class outfit, downside only to the wallet.

[newhaul]

Originally Posted by john61ct

NMC is a completely different chemistry from LFP, different charging profile, temperature issues, nowhere near the same lifetime cycles potential. . .

IMO this question is worth its own thread, an extensive discussion would dilute the value of this one.

That said Victron is a class outfit, downside only to the wallet.

not to mention the fire potential of NMC vs the relative safety of Lfp .

[CatNewBee]

Hi there,

just wanted to inform you about some long-term testing results with Winston LiFeYPO4 cells, heavily abused over 7 years in a off-grid set up at one of the German LFP pros shed. He runs a business in building and providing custom LFP batteries for RV usage, is doing it for many years and has a similar reputation in the German RV forum like Maine Sail here in the CF forum.

For those of you, who can read German here is the link to the discussion thread:

https://www.wohnmobilforum.de/w-t118991.html

Bottom line is:

he has a battery built of 4x 160Ah Winston cells, uses 300W solar to charge and floats the cells at 14.7V on a lead acid profile with the charge solar controller, He does this all year long, also cycles the batteries and has other sets of cells he also disconnects and stores over the winter and re-enables them for the next season.


The findings are, after 7 years of charging and keeping the cells at 14.2...14.7V almost daily, they show no signs of capacity degradation - so the assumption of high storage / absorption voltages, even float of 14.7V over 7 years show no negative effects yet on the cells. The full capacity test (Discharge to the cut-off point) is performed once per year to monitor degradation, the cells are exposed to the elements outside of a building, so the temperature varies between sub zero during the winter and high temp in the summer, also the cells are re-charged and kept kept at float over 14.2V during the winter when the solar panels are covered by snow by a B2B charger from a larger LFP house bank.

Second finding was, that cells of disconnected PSOC batteries tend to run out of balance and have significant voltage differences when re-enabling the battery, what leads to long balancing and heat at the balancer modules. However the battery goes back in sync and recovers to almost full capacity after a few cycles when allowing it to sync by longer Absorption phases.

He has the impression, that storing and keeping the battery full even at float with crazy 14.7V (setting absorption=float) seems to be better for the battery than disconnecting and storing it half discharged. Also he finds a capacity loss on disconnected stored cells more likely, the cells seem to be more sensitive to low voltages and storage on lowed SOC regarding capacity than on being all the time at 100% SOC.

The tests were done on a real use scenario with inverter usage and occasionally charging in temperatures sub zero.

It contradicts diametrically the "common sense" of the experts here to never charge the cells to full for longevity and never store them at high SOC.

The LFP seem to be much more robust to high voltage than postulated here.

Just wanted to let you know.

[Delfin]

Originally Posted by CatNewBee

Hi there,

just wanted to inform you about some long-term testing results with Winston LiFeYPO4 cells, heavily abused over 7 years in a off-grid set up at one of the German LFP pros shed. He runs a business in building and providing custom LFP batteries for RV usage, is doing it for many years and has a similar reputation in the German RV forum like Maine Sail here in the CF forum.

For those of you, who can read German here is the link to the discussion thread:

https://www.wohnmobilforum.de/w-t118991.html

Bottom line is:

he has a battery built of 4x 160Ah Winston cells, uses 300W solar to charge and floats the cells at 14.7V on a lead acid profile with the charge solar controller, He does this all year long, also cycles the batteries and has other sets of cells he also disconnects and stores over the winter and re-enables them for the next season.


The findings are, after 7 years of charging and keeping the cells at 14.2...14.7V almost daily, they show no signs of capacity degradation - so the assumption of high storage / absorption voltages, even float of 14.7V over 7 years show no negative effects yet on the cells. The full capacity test (Discharge to the cut-off point) is performed once per year to monitor degradation, the cells are exposed to the elements outside of a building, so the temperature varies between sub zero during the winter and high temp in the summer, also the cells are re-charged and kept kept at float over 14.2V during the winter when the solar panels are covered by snow by a B2B charger from a larger LFP house bank.

Second finding was, that cells of disconnected PSOC batteries tend to run out of balance and have significant voltage differences when re-enabling the battery, what leads to long balancing and heat at the balancer modules. However the battery goes back in sync and recovers to almost full capacity after a few cycles when allowing it to sync by longer Absorption phases.

He has the impression, that storing and keeping the battery full even at float with crazy 14.7V (setting absorption=float) seems to be better for the battery than disconnecting and storing it half discharged. Also he finds a capacity loss on disconnected stored cells more likely, the cells seem to be more sensitive to low voltages and storage on lowed SOC regarding capacity than on being all the time at 100% SOC.

The tests were done on a real use scenario with inverter usage and occasionally charging in temperatures sub zero.

It contradicts diametrically the "common sense" of the experts here to never charge the cells to full for longevity and never store them at high SOC.

The LFP seem to be much more robust to high voltage than postulated here.

Just wanted to let you know.

Let the fun begin....

[Delfin]

The discussion comments in the link are also interesting.

[john61ct]

Very interesting.

Storage in such cold conditions would be very conducive to longevity.

I believe it is the very high SoC regime generally that is causing the unbalancing.

I assume when manually starting out he also top-balances?

I bet the cells are not being full isolated in storage, lots of cell-level BMSs will create long-term problems, really have no function in a storage context so IMO should not be left on.

And relying on a very low-balance current BMS for restoring major un-balance seems sub-optimal.

I wonder how much Winston's Yttrium doping changes the LFP characteristics?

7 years including long non-cycling seasons IRL is likely well under 1500 cycles, not long at all.

Isolating the impact of some of these variables on longevity in the range of 10000-20000 cycles, would require a precise well automated test rig, and holding to lower C rate levels really slows things down.

[CatNewBee]

There are several tests running at his shed. One is the long term float test with a 160Ah battery, now running 7 years, while keeping the battery most of the time above 14.2..14.7V.

The second is the disconnected storage and re-activation afterwards of another battery. The findings there are, the cells drift when disconnected. Some discharge internally faster than others, the voltage stability gets lost (caused also by increased internal resistance), but it seems to be not a permanent damage. The result is, the battery needs extended balancing and several cycles to return to full capacity when awaking it from the storage, while the floated battery do not show any degradation.

The third one is the effect of lover cell voltages in disconnected storage, especially when they go down un-monitored. Here comes the contribution in the thread about how to rescue a cell that is almost empty after disconnected storage by very low charge currents for the first 20..30% of charge. The revival must be done with very slowly, otherwise you risk inflation of the cells and serious mechanical damages.

Bottom line was: cells held in float over the winter are better off than disconnected cells, even abusive high voltages in the upper shoulder do not harm as much as lower voltages in disconnected cells, what he was not expecting in the first place. His setup was to find out how fast the cells will degrade when floated at 14.7V (3.675V) all the time and what damage FLA controller / charger may cause on LFP batteries - surprisingly he found in 7 years none. He uses a cheap dumb Steca FLA solar controller for the test, the one similar to mine that was responsible to wreck and boil my Excide equipment gel house battery before I went to rebuilding the electric installation of the Cat to LFP. I was not aware of it when purchased the vessel 2nd hand.

The high voltage regime keeps the cells perfectly in balance, because the balancer are active all the time at this set point / daily re-charge. The test was not meant to find out how many cycles the battery will do (assumption is, more than you can wait for), but to see the impact of solar and permanent float / high voltage storage / use of lead acid chargers and the damages caused by it.

So, lessons learned.

[tanglewood]

Originally Posted by CatNewBee

So, lessons learned.

Indeed. It's a good reminder that we don't know anywhere near as much about this chemistry as we might think.

[Delfin]

Originally Posted by tanglewood

Indeed. It's a good reminder that we don't know anywhere near as much about this chemistry as we might think.

True dat.

I would really like to see this replicated before accepting that much of what we currently think about this technology is incorrect. Although I have to say that the idea that cells in storage may drift due to different rates of self discharge has the ring of plausibility, and may argue for more frequent top balancing via the BMS.

[mat jam]

I read the first few pages and the last ten or so pages so apologies if this has been covered, but what I gleaned was that there are too many unknowns with such a complex thing that has too many variables that requires a management system which is another thing that can go wrong.


LiFePO4 Battery 101


This guy worked at JPL on the Mars Rover.

https://www.youtube.com/watch?v=QlDd3jkcxoQ

Thickness of electrodes determines discharge efficiency rate. Thinner is much more effective and more expensive. Higher discharge rate creates heat which breaks down the electrolytes which ultimately affects life cycle. Short term heating is good, but it is specific to each cell structure and the required regimen to follow would be difficult for most cruisers to implement, especially without guidelines from the manufacturer. Long term heating is bad, period. And the higher the current discharge equals less and less energy available. So the bottom line is the battery manufacturers should be publishing the safe discharge load range for long term use efficiency. If you are pulling a constant rate of energy from the batteries within the range then your batteries will provide a longer life cycle. If you are putting high discharge loads on your batteries expect a shorter life cycle. If your use is on the higher SoC then you can expect thousands of cycles. If your use is on the lower SoC you can expect hundreds of cycles. Also says some interesting things about BMS and individual Cells.


And pulse charging regimen is better than a constant current. With a properly engineered cell (all cells equally balanced) potentially charge 40-50% faster with a pulse technique. And add about 10% life cycle. So the question is with so many charging methods being utilized on a boat – diesel, shore, solar, etc. how will this effect the life cycle?


I have read elsewhere stated that with Lithium batteries you can expect 7 years if you do not go below 50% SoC without proper battery management and 10 years if you do not go below 50% SoC with proper battery management. Charge at 3.4 V. Above 4.3 V the electrolyte starts to break down. Do not let it go below 1.0 V. Fast charging and fast venting can cause a spark and an explosion. Stay under 50 C for longevity. Stay under 100 C for safety. They may fail or blow up. The vents are potential areas where water can get in and contact with the electrolyte is not good (dangerous). And use of aluminum foil only makes this worse. So essentially, if you thought you can take it down to 20% and put high loads on it and still get thousands of cycles...


Conditioning a battery (all cells equally balanced) and a starting regimen is very important. Management is very important. Seems like a lot of work for a cruising lifestyle.


He also mentions that LA with the proper regimen is really good and is amazing what you can do with it and that you can use a technique for removing the sulfation which I think most already know.


Some of this info may be outdated.

[Delfin]

Originally Posted by mat jam

I read the first few pages and the last ten or so pages so apologies if this has been covered, but what I gleaned was that there are too many unknowns with such a complex thing that has too many variables that requires a management system which is another thing that can go wrong.


LiFePO4 Battery 101


This guy worked at JPL on the Mars Rover.

Thickness of electrodes determines discharge efficiency rate. Thinner is much more effective and more expensive. Higher discharge rate creates heat which breaks down the electrolytes which ultimately affects life cycle. Short term heating is good, but it is specific to each cell structure and the required regimen to follow would be difficult for most cruisers to implement, especially without guidelines from the manufacturer. Long term heating is bad, period. And the higher the current discharge equals less and less energy available. So the bottom line is the battery manufacturers should be publishing the safe discharge load range for long term use efficiency. If you are pulling a constant rate of energy from the batteries within the range then your batteries will provide a longer life cycle. If you are putting high discharge loads on your batteries expect a shorter life cycle. If your use is on the higher SoC then you can expect thousands of cycles. If your use is on the lower SoC you can expect hundreds of cycles. Also says some interesting things about BMS and individual Cells.


And pulse charging regimen is better than a constant current. With a properly engineered cell (all cells equally balanced) potentially charge 40-50% faster with a pulse technique. And add about 10% life cycle. So the question is with so many charging methods being utilized on a boat – diesel, shore, solar, etc. how will this effect the life cycle?


I have read elsewhere stated that with Lithium batteries you can expect 7 years if you do not go below 50% SoC without proper battery management and 10 years if you do not go below 50% SoC with proper battery management. Charge at 3.4 V. Above 4.3 V the electrolyte starts to break down. Do not let it go below 1.0 V. Fast charging and fast venting can cause a spark and an explosion. Stay under 50 C for longevity. Stay under 100 C for safety. They may fail or blow up. The vents are potential areas where water can get in and contact with the electrolyte is not good (dangerous). And use of aluminum foil only makes this worse. So essentially, if you thought you can take it down to 20% and put high loads on it and still get thousands of cycles...


Conditioning a battery (all cells equally balanced) and a starting regimen is very important. Management is very important. Seems like a lot of work for a cruising lifestyle.


He also mentions that LA with the proper regimen is really good and is amazing what you can do with it and that you can use a technique for removing the sulfation which I think most already know.


Some of this info may be outdated.

Different chemistry than the LiFePO4 batteries discussed in this thread.

[mat jam]

Originally Posted by Delfin

Different chemistry than the LiFePO4 batteries discussed in this thread.

He discusses the basics of all LifePO4 batteries - hence - 101. Any difference would be in the chemical make-up of the electrolyte. If as you suggest it is a different chemistry altogether would it not have a different designation? I along with many are trying to understand these batteries. And are you stating that what he states in the video does not apply? If so, what does not apply and what does? Specifically, what is so different of the chemical structure to devoid the facts in the video when he is giving an overview of LifePO4 batteries?

[CatNewBee]

Originally Posted by mat jam

.... Charge at 3.4 V. Above 4.3 V the electrolyte starts to break down. Do not let it go below 1.0 V. Fast charging and fast venting can cause a spark and an explosion. Stay under 50 C for longevity. Stay under 100 C for safety. They may fail or blow up. The vents are potential areas where water can get in and contact with the electrolyte is not good (dangerous). And use of aluminum foil only makes this worse. So essentially, if you thought you can take it down to 20% and put high loads on it and still get thousands of cycles...


Conditioning a battery (all cells equally balanced) and a starting regimen is very important. Management is very important. Seems like a lot of work for a cruising lifestyle.


He also mentions that LA with the proper regimen is really good and is amazing what you can do with it and that you can use a technique for removing the sulfation which I think most already know.


Some of this info may be outdated.

Well this is ridiculous. You should check the tech data of a LiFePO4 / LiFeYPO4 cell.

Cell is full at 3.65V, 3.4V would not even charge it to 60%, because there will be no charge current. You can expect cell damage below 2.8V, at 1.0V the cell is definitely dead. When you charge a cell, that is deep discharged, it can inflate and burst, so do this with very low current over a long time to try to recover a deep discharged cell. Initial charge and conditioning is done up to 4.0V to the specs, once done, you should not exceed 3.65V while charging.

Also keep the cells balanced, this is important. Unbalanced cells drift faster and lead to capacity reduction and possible disconnects of the battery despite being in a "safe voltage" range of the pack, because a single cell either runs above the protection threshold while charging or below the threshold while discharging provoking failures in operation. Assume you sail around and look at your gauge, it reads 13 V and suddenly the battery disconnects because of the deep discharge protection. The reason is, 3 cells are at 3.4V and one is at 2.8V because she is out of balance triggering LVP signal.

Also keep in mind, most BMS cell modules bypass part of the current when the respective cell voltage is over 3.6V. Usually they burn 1.0...2.5A while balancing. If your pack voltage is 13.6V (3.65V cell voltage) and all cells are balanced, and you measure a current of 1.0...2.5A, that means, there is no charge current to the cells at all, what you see is the bypass current of the 4 cell modules only, heating up the environment with 13.6...34W

I know the 101, I have posted it somewhere in this thread - it discusses the chemistry and also the extremes that occur outside of the shoulders and the implication for use in mobility applications. When you use LFP batteries as house battery you want to stay in the safe operational voltage, current and temperature range, so stick to the specs. The LFP battery with a good BMS is a "set it and forget it" device, it needs less maintenance than a FLA battery, it does not require human interaction.

[Delfin]

Originally Posted by mat jam

He discusses the basics of all LifePO4 batteries - hence - 101. Any difference would be in the chemical make-up of the electrolyte. If as you suggest it is a different chemistry altogether would it not have a different designation? I along with many are trying to understand these batteries. And are you stating that what he states in the video does not apply? If so, what does not apply and what does? Specifically, what is so different of the chemical structure to devoid the facts in the video when he is giving an overview of LifePO4 batteries?

What I was referring to was your summary of the characteristics and difficulty of management of LiFePO4 batteries. Not much of it applies to that chemistry, or the systems on boats as CatNewBee also notes.