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

[evm1024]

Originally Posted by OceanSeaSpray

Wrong. Another contributor from Australia a few years go reported how he had to "service" all his RV installations every 3 years or so because they were running out of capacity. That was in excess of 100 of them if I remember correctly.

You need to measure capacity to identify issues and this requires doing a full controlled charge or discharge cycle. Most people never do that, or only at the very beginning, and then just keep claiming that everything is great and as good as new.



I have already done that if you actually read the material, but the fine detail is that I started recharging with the pack very close to the bottom, 2.95V/cell or so, and recharged continuously until the termination condition was hit while metering the current. There are no "misconceptions". Within 1-2% of capacity at the very most, that is what it is.
After the charge, the cell voltage settled back down to a value abnormally low for fully recharged cells and in agreement with the charge supplied. This is a tell-tale of memory effects and precisely what prompted me to formally measure the available capacity. When a 4S pack has been fully recharged, the voltage under light load should hold above 13.3V for about 0.2C. If this doesn't happen, there is an issue somewhere.

I too have been seeing some loss of capacity. I've got 5 years on my 700 AH bank. Which now gives about 500 AH in a capacity test, About 70%.

I have not run capacity tests in years - as noted the bank acts normally. Charges up much the same as always. There are 2 "weaker" cells that increase in voltage faster than the other 2.

Discharge is normal - the cells track within 10 mV or less and just deliver amps as needed.

Charging is irregular and I only get to 100% rarely. Mostly the cells sit around 50%.

Without a capacity test I had no idea that I was "only" getting 500 AH.

The test was prompted because I changed out the older Xantrex Charger/Inverter for a Victron unit.

SO - I would be very interested in seeing what works to restore some or all of the "lost" capacity.

A new thread or keep it here, that is the big question.

[OceanSeaSpray]

Originally Posted by Maine Sail

I have actually done that, every 50 cycles to 1000 cycles, and now doing it every hundred cycles as it really just got tiresome...

As we discussed in emails our pack shows no sign of memory issues but we are getting to 100% SOC at least every 20 +/- cycles and at the worst every 50 cycles... Our most frequent charge source is about .35C. I wonder if memory effect may also be related to low charge rates stacked on top of many months PSOC cycles?

A low charge rate should help with achieving higher SOC... In any case, the research indicates that memory effect is the result of failing to recharge completely and it becomes more and more noticeable with the number of aborted charge cycles, especially if they all stop in the same place. I will have had well over a thousand of these by now, stopping anywhere randomly. When the energy was available to fully charge, the charging regime used was obviously not enough to (fully?) overcome the cell memory in spite of the 3.5V/cell absorption voltage etc. As a result, it has been getting worse.

At this stage, this seems to suggest that charging should probably be adaptive and take into account the cycling history.

In this case, I started charging at about 0.7C and then the pack went into absorption for over an hour and the current stayed very low for most of that time. At the end, the apparent resistance of the pack was very high, about 125mOhms, but only for charging. Another curious thing I observed was that if I suddenly discharged some capacity, I could put that straight back in at high current, but I would hit the wall again at the same point again after that.
I hoped that the next full charge cycle after that would be easier and take me further, but it didn't.

The fact that you went up to 50 cycles with partial recharging only and then successfully returned to a full charge is a valuable piece of information, thanks for that.

[OceanSeaSpray]

Originally Posted by evm1024

I too have been seeing some loss of capacity. I've got 5 years on my 700 AH bank. Which now gives about 500 AH in a capacity test, About 70%.

I have not run capacity tests in years - as noted the bank acts normally. Charges up much the same as always. There are 2 "weaker" cells that increase in voltage faster than the other 2.

Discharge is normal - the cells track within 10 mV or less and just deliver amps as needed.

Charging is irregular and I only get to 100% rarely. Mostly the cells sit around 50%.

Without a capacity test I had no idea that I was "only" getting 500 AH.

The test was prompted because I changed out the older Xantrex Charger/Inverter for a Victron unit.

SO - I would be very interested in seeing what works to restore some or all of the "lost" capacity.

A new thread or keep it here, that is the big question.

This is strikingly similar, thanks for sharing it. I think this situation is much more common than it seems, it is just that it is not very visible until it is very late, or until you go and actually look for it.

Happy to move to a LFP memory effects thread. It will be a little while before I have more information to share about remediation, but the answer will be in the direction of "keep charging".

[evm1024]

Originally Posted by OceanSeaSpray

This is strikingly similar, thanks for sharing it. I think this situation is much more common than it seems, it is just that it is not very visible until it is very late, or until you go and actually look for it.

Happy to move to a LFP memory effects thread. It will be a little while before I have more information to share about remediation, but the answer will be in the direction of "keep charging".

Yes, the 70% comes up a few times here and there.

Are you thinking of a new thread to handle the "70%" issue or using the "LiFePO4 battery capacity decreasing" thread?

It would be nice to have a thread that only has posts by those who have direct experience with dealing with and trying to reverse the memory effect.

OK so here is one such thread.

LFP memory effects thread - Cruisers & Sailing Forums

If you have experience with this effect or direct information on its cause or remediation please do post there also.

[tanglewood]

Originally Posted by OceanSeaSpray

A low charge rate should help with achieving higher SOC... In any case, the research indicates that memory effect is the result of failing to recharge completely and it becomes more and more noticeable with the number of aborted charge cycles, especially if they all stop in the same place. I will have had well over a thousand of these by now, stopping anywhere randomly. When the energy was available to fully charge, the charging regime used was obviously not enough to (fully?) overcome the cell memory in spite of the 3.5V/cell absorption voltage etc. As a result, it has been getting worse.

At this stage, this seems to suggest that charging should probably be adaptive and take into account the cycling history.

In this case, I started charging at about 0.7C and then the pack went into absorption for over an hour and the current stayed very low for most of that time. At the end, the apparent resistance of the pack was very high, about 125mOhms, but only for charging. Another curious thing I observed was that if I suddenly discharged some capacity, I could put that straight back in at high current, but I would hit the wall again at the same point again after that.
I hoped that the next full charge cycle after that would be easier and take me further, but it didn't.

The fact that you went up to 50 cycles with partial recharging only and then successfully returned to a full charge is a valuable piece of information, thanks for that.

You mention research in this memory effect. Would you have any pointers to that? I’d be real interested to read about it.

[sparrowhawk1]

Here's a comparison between a cheap PWM and an MPPT controller. Of course there's going to be a huge difference in comparing series to parallel. I'm just interested in the parallel comparison.https://youtu.be/neaTgRlxRwk
I have that cheap controller and it says not to disconnect from the battery when the solar panel is connected so I don't see how he can use it with a battleborn ("drop in")

[OceanSeaSpray]

Originally Posted by tanglewood

You mention research in this memory effect. Would you have any pointers to that? I’d be real interested to read about it.

T. Sasaki, Y. Ukyo and P. Novak, "Memory effect in a lithium-ion battery", Nature Materials, Vol. 12, June 2013; doi:10.1038/nmat3623

[OceanSeaSpray]

I will now move to LFP memory effects thread - Cruisers & Sailing Forums for further discussions.

[newhaul]

Originally Posted by sparrowhawk1

Here's a comparison between a cheap PWM and an MPPT controller. Of course there's going to be a huge difference in comparing series to parallel. I'm just interested in the parallel comparison.https://youtu.be/neaTgRlxRwk
I have that cheap controller and it says not to disconnect from the battery when the solar panel is connected so I don't see how he can use it with a battleborn ("drop in")

here is a direct comparison that mainesail did a few years ago

[john61ct]

The full post https://marinehowto.com/mppt-vs-pwm-solar-controllers/

[sparrowhawk1]

So in a nutshell lithium batteries voltage vairies much less than lead acid having less differential at first but staying in bulk mode for much longer. Resulting in an average of 20% more amp hours. So I'm back to either buying an adjustable mppt controller ($150) or figuring out a way to use my 40a mppt controller that can only be set to sealed at 14.4 which when tested was actually 14.2 at the batteries when charging at 20 amps because the controller gets its reading off of the same leads that charge the battery. I'm just worried that at a lower amperage the voltage will be too high. Experienced people say different things. Keep in mind I'm planning on starting out small with maybe a hundred amp hour battery Bank that I can buy for less than $450 new. Free shipping. Same bank that Will Prowse used in his video.
Or even taking a gamble with used batteries with an eBay seller who has a high rating.

[sparrowhawk1]

Oops. The cells that go for 105 each have shipping that makes them more expensive than these https://www.amazon.com/LiFePO4-Lithi.../dp/B07PV5FCYX
I'm sure by the time I'm ready the price will come down more.

[john61ct]

Originally Posted by sparrowhawk1

So in a nutshell lithium batteries voltage vairies much less than lead acid having less differential at first but staying in bulk mode for much longer

As long as the C-rate stays within ranges lead is capable of, and between 10-90% SoC, yes.

At the shoulders, or at extreme current rates, no.

> Resulting in an average of 20% more amp hours

not sure what you mean? but if "usable capacity" going to deeper DoD per cycle, yes even more than that, depending if you want to go for crazy-long lifespan or not.

> Or even taking a gamble with used batteries

IMO only go that route if

as you say, seller's rating is very high, ideally lots of transactions over time, and

price - including delivery - is less than 15% of the new price, so who cares if near EoL,

OR (
the auction is not flagged as "For Parts Only", AND

they are being shipped via tracked method that can be verified online (no "for local pickup", no Uship.com), AND

you have the capacity to at least ballpark load-test for actual capacity soon after arrival, AND

the seller makes a specific claim about capacity still being high ("hardly used" etc),

so you are protected by eBay's NQAMBG
)

You still may have to cover return shipping, and that can be hard/expensive as they are Hazmat rated goods.

Above is all from hard-won experience, out of several thousand Ah purchased this way so far, I have gone from foolishly losing hundreds of dollars, to more recently saving many thousands.

_______
And yes, just get a better controller, nothing to do with LFP really, any expensive chemistry deserves precision and adjustability.

[KTP]

Seems really expensive to pay $600 for raw cells with no bms when packaged LFP solutions with warranties are $900 to $1000.

[sparrowhawk1]

Both Will Prowse and mainesail show 20% increase w MPPT over PWM.

Attachment 194374
This is mainesails breakdown
Will did it in full sunlight

And yes I understand conditions will be different all the time, state of charge, c rate, time, etc.