Most useful article I've ever found on LFP battery charging

[Maast]

Came across this as a reference in a thread, it's possibly the most useful article I've ever came across about LFP charging regimes. Evidently there actually is a well documented memory effect on LFP cells and that always holding charge voltages low to avoid overcharging the cells is counterproductive. The author recommends a periodic full charge and discharge to 'recondition' the cells.

Marine lithium batteries in operation | Nordkyn Design

This article details the relations between voltage, state of charge, current and temperature for lithium iron phosphate (LFP or LiFePO4) battery banks.

nordkyndesign.com

 

[upnorthandpersonal]

Cold temperatures are known to be detrimental to the cells if they are exposed to charging. Cycling performance tests at varying temperatures showed the apparent existence of a threshold below which capacity fade with cycling suddenly accelerated. This threshold appeared to be above the temperature of 0°C often suggested as limit for recharging, but the data available was limited and the exact details of cell manufacture are likely to influence this value.

Emphasis mine.

I figured this was the case. I always have my cut-off temperature well above 0°C, preferably at 5°C or even higher. Seeing people putting it right at 0°C seemed a bit off.

 

[Maast]

Supporting documentation, info-dense read though. Oh the irony, we still need what is effectively a "equalization" charge periodically and I have no idea of how to automate that with my Midnites. I might have to rig something up with a power supply and long duration time delay relay control boards for once a month or so after the system gets inspected by the county after install is complete.

 

[gnubie]

Really has me wondering how the all-in-one MPPs handle lithium charging now. They should be able to watch the battery current directly.

 

[Maast]

Everything the author writes on the subject is gold and I wish I'd come across it a lot sooner.

Like this one on LFP battery bank assembly: http://nordkyndesign.com/assembling-a-lithium-iron-phosphate-marine-house-bank/

Or anything on the subject of LFP batteries: http://nordkyndesign.com/category/marine-engineering/electrical/lithium-battery-systems/

 

[Maast]

I think I'll just attach a PSP-300-48 power supply to a standard high reliability timer and set it to one day a month but otherwise keep the charge profile down to 3.4v

 

[Dzl]

Came across this as a reference in a thread, it's possibly the most useful article I've ever came across about LFP charging regimes. Evidently there actually is a well documented memory effect on LFP cells and that always holding charge voltages low to avoid overcharging the cells is counterproductive. The author recommends a periodic full charge and discharge to 'recondition' the cells.

Marine lithium batteries in operation | Nordkyn Design

This article details the relations between voltage, state of charge, current and temperature for lithium iron phosphate (LFP or LiFePO4) battery banks.

nordkyndesign.com

I have that website bookmarked, but have yet to read the article(s) in full.

Coincidentally, this article which is the 'most useful article on lithium batteries' that I've come across so far, also touches on some of these same issues. The author does a full capacity test every 50 cycles and after 772 cycles has what appears to be slightly greater capacity than when he began testing. His hypothesis as to why there has been no capacity loss is that the every 50 cycle full charge and discharge helps keep any potential memory effect to a minimum. I'm oversimplifying a bit, but I think that is the gist of it, and it seems to corroborate the theory from the article you cited.

 

[upnorthandpersonal]

Time to buy some of those cells off of Aliexpress and set up a test set-up for myself I think.

 

[Steve_S]

I have that website bookmarked, but have yet to read the article(s) in full.

Coincidentally, this article which is the 'most useful article on lithium batteries' that I've come across so far, also touches on some of these same issues. The author does a full capacity test every 50 cycles and after 772 cycles has what appears to be slightly greater capacity than when he began testing. His hypothesis as to why there has been no capacity loss is that the every 50 cycle full charge and discharge helps keep any potential memory effect to a minimum. I'm oversimplifying a bit, but I think that is the gist of it, and it seems to corroborate the theory from the article you cited.

The link to MarineHowTo you provided IMO should be a MUST READ like the Nordkyndesign ones... Sure explains a LOT and makes no bones about it.... IN particular how & what a BMS is supposed to do and best charging profile info...

 

[SolarRat]

Like I've been saying, todays charge controllers are just lead acid chargers with just enough user adjustable settings so they can slap a "for lithium" label on them...

LFP is still in it's relative infancy. There's a lot we still don't know, and the ones "in the know" are not giving up their trade secrets so easily. I've been reading the links above the past few months and those guys grasp a lot of the challenges, but even they are still learning and are not always 100% correct (but probably a lot closer than most).

Battery manufacturers hold all the secrets. They don't care about us DIYers. They sell to huge companies, not just the batteries but charger design info too. They are not freely giving this type of information to you or I...or Victron, MPP Solar or Epever for that matter.

 

[gnubie]

It's an interesting point. Victron has its own range of lithium batteries. If the lifepo4 charging profile in their SCCs cause the sort of damage the article suggests is possible, that will mean there could be a substantial number of warranty claims. At least Victron will honour the warranty and will be around to do it.

 

[SolarRat]

It's an interesting point. Victron has its own range of lithium batteries. If the lifepo4 charging profile in their SCCs cause the sort of damage the article suggests is possible, that will mean there could be a substantial number of warranty claims. At least Victron will honour the warranty and will be around to do it.

Victron doesn't make their own batteries. They use CALB or Winston cells (I forget which). The BMS they use was also probably recommended by or designed by the battery manufacturer. Did they also help design their charge profiles?...not sure

 

[gnubie]

Who said they did? They have their own range, ie a product line.

 

[SolarRat]

Who said they did? They have their own range, ie a product line.

Just clarifying for the majority that probably don't realize that.

If a Victron has a bad cell, who eats the warranty cost, Victron or Winston?

 

[SolarRat]

My guess is the manufacturers are not responsible for lost capacity due to memory effects (would fall under "improper charging").

IF there is even such a thing as a memory effect on lithiums?...

 

[gnubie]

Yes, it is IF at this point. My point was that if Victron has range of lithium batteries and a range of SCCs with lifepo4 profiles specifically to charge their lithium batteries, improper charging shouldn't be an out, unless of course the charging profile has been modified or not used.

 

[SolarRat]

Victron only warranties their batteries for 2 or 3 years. IF memory problems are real they probably won't be pronounced enough to trigger a warranty claim in that timeframe. Getting 5 years out of a quality LFP should be easy with any CC from a decent company...but will they still be going strong at 10 years without some end-user help? Most people who post about their 10 year old battery banks are way above the average user in terms of electrical expertise and test equipment. They've surely done capacity tests throughout the years which exercised the banks.

 

[Steve_S]

One of the,main reasons that Victron, Trojan, Rolls Surette LFP Battery packs cost as much as they do, they buy guaranteed & tested cells that meet "their specs", not just some random pull off the assembly line. They stand behind the product they stick their label on and they eat the cost "if" it is a Warranty issue but NOT if it is a User Abuse issue. IN the case of Victron, they have their profiles setup to match their LFP offerings which can be tweaked.

LFP has no memory it is NOT NimHi, NiCad or those other horrible batteries of the past which did set a charge memory. Again the old wives tales progress to new batteries & new chemistries... hen of course the FUDster's push such as an argument against Renewable Energy. What is a FUDster, it is someone or some group pushing "Fear, Uncertainty & Doubt" in regards to any technology or science. It can be highlighted quite well by the Anti-Tesla goons who attack everything out of context to portray things negative and to keep people from considering an EV...

 

[upnorthandpersonal]

Please read the article. There might very well be memory effects, even if they're not as pronounced as on other chemistry. However these memory effects do occur in specific circumstances, and if batteries are charged wrong, these might very well cause issues. This has nothing to do with FUD. I've been reading the nordkyndesign articles for the past day or so, and they are very well written and properly sourced with references and I don't see any obvious bias.

 

[SolarRat]

I remember what a FUDster is. You called me one when I warned you to stay away from Shun-Bin..... Sometimes FUDsters are correct.

 

[Maast]

LFP has no memory it is NOT NimHi, NiCad or those other horrible batteries of the past which did set a charge memory.

Yeah, it does, not nearly as bad as the others but it exists. It was a shock to me too. Don't take my word for it - read the first link, and then the PDF study I posted, then google the subject and read more papers. I just posted the two best documents I found on the subject but I found many many many more.
The good news is it's reversible if you carefully do a perodic full charge without overcharging it - Dont watch the voltage watch the current go to 0 or near-0 and then stop charging. Don't float.

 

[grizzzman]

Yeah, it does, not nearly as bad as the others but it exists. It was a shock to me too. Don't take my word for it - read the first link, and then the PDF study I posted, then google the subject and read more papers. I just posted the two best documents I found on the subject but I found many many many more.
The good news is it's reversible if you carefully do a perodic full charge without overcharging it - Dont watch the voltage watch the current go to 0 or near-0 and then stop charging. Don't float.

Not always. If allowed to under charge long enough, it may become a permanent loss.

 

[electric]

Oh my God, red line has slightly deviated from the black line, call the Nobel Prize committee, we discovered that sky is falling on all LFP batteries.
This will be chewed, regurgitated, chewed again and again until no longer recognizable in all social media for the next 10 years.
You guys are a funny bunch...

 

[upnorthandpersonal]

From the text:

The memory effect was found to strengthen with the number of incomplete charge cycles performed before the erase cycle. It was also strengthened when a partial charge was followed by a shallow discharge, rather than a deep discharge.

and

These latter aspects have proved to be of key significance when considering the longer term performance of LiFePO4 batteries in house bank applications, because incomplete charge cycles are common when relying on renewable energy sources and shallow discharge cycles are also frequently experienced. These have the potential to render battery banks near unusable after as little as 2-3 years in regular service in the absence of memory-releasing cycles. Ineffective memory-releasing cycles are very common in DIY installations where the charging process is not properly controlled and/or configured incorrectly by fear of overcharging or due to widespread mythologies.

Are they minimal? Probably. The sky isn't falling. Are they good to know about so systems can be designed better and last longer? I would say, definitely.

 

[Maast]

I asked the original author and got an answer. It appears a completely full charge using current taper to find the termination point once or twice a year is sufficient. My current equipment can't do it so it'll have to be a manual "memory wipe" but at only a couple times a year this is acceptable.

Am I making much ado about not much? I dont think so and the science behind it is more than solid even though it's not common knowledge, maybe because people dont WANT to believe it.

I've got more money invested in my battery bank than my first three cars I owned - combined! I saved for years to build my system. You damn well better believe I'm going to do everything I can to get full use out of it for as long as is achievable.

I’m a little late to the party here, but I have to ask: how often should a full charge be accomplished to wipe memory effects before they become permanent? Once a month? 6 months? a week? I’ve got 3 55A Midnite Classic 250s charging my 50kwh LFP bank w/ a Radian GS8048 inverter. I can adjust the bulk and adsorption voltages & time, and turn off the float.
Nothing I have allows me monitor current and get that information into the Midnites or Radian in a useful way.
The only way I can see accomplish a periodic full charge is to set the equalize function to 3.6v/cell and the time to a value I establish w/ a current monitor to when the charge current gets to 0 or near 0 and then have it repeat once a week/month/etc.
If you have any ideas I’d love to hear them.
Thanks

Eric Bretscher says:
30 December 2019 at 7:46 am

Memory effects don’t become permanent, they just become more difficult to overcome. Your question is difficult to answer because there is not much data available and it depends too much on the operating regime of the bank. Performing a full recharge once or twice a year would appear to be quite enough in most cases.
If you can’t monitor current and use this information, you can’t achieve a correct charge termination. The absorption time varies a lot with the condition (and age) of the cells, so trying to deterine a fixed absorption time is a flawed strategy. You must use voltage and current.
Trying to charge LFP banks with lead-acid chargers doesn’t work properly. The BMS must measure the current and be able to control the charge termination.
Best regards,
Eric