Charging LFP below 32F - 0C freezing temperature - possible - with newer chemistry?

[eXodus]

We are getting drilled in by Will and other people knowledgeable about the subject - do not charge below freezing.

Like every other knowledge - that piece of advice has an expiration date - since technology moves on.

There are more and more manufacturers are coming out - saying - we don't do low temperature -cut off, but low temp charge limitation.
"When charging lithium iron phosphate batteries below 0°C (32°F), the charge current must be reduced to 0.1C and below -10°C (14°F) it must be reduced to 0.05C. Failure to reduce the current below freezing temperatures can cause irreversible damage to your battery. "

How do LiFePO4 batteries perform in cold temperatures? | RELiON

How do LiFePO4 batteries perform in cold temperatures?

www.relionbattery.com

Can be charged at temperature down to -20°C for cold weather use (sub Zero version)

Charging Your Lithium Battery Below Zero - DC Battery Technologies

How to correctly charge your Lithium Battery is a frequently asked question. By following this simple guide, you will have all the knowledge to look after your battery efficiently!

dcbattery.tech

My first chemistry question was when looking deeper into the subject - why is everyone focused on the freezing point of water? There is no H2O in common LFP chemistries. Every solution has a different freezing point - it would be quite a coincident that all batteries are freezing a 32F 0C.

My potential unpopular opinion on the subject:
All that public bashing on missing low temp CUTOFF is leading manufacturers to not develop low temperature chemistries.

There is still research going on low temp charging , but not as much as there could be, with the single minded focus of the DIY video publishing community - in ripping batteries apart and putting sensors ins freezing WATER and waiting for the current to drop to zero.

Study on the Capacity Fading Effect of Low-Rate Charging on Lithium-Ion Batteries in Low-Temperature Environment

By taking a cylindrical LiFePO4 power battery as the research object, the cycle performance test was conducted under different charging current aging paths in a preset low-temperature environment and combined with EIS results to analyze the dynamic characteristics of the battery during the aging...

www.mdpi.com

When you look at various scientific studies - you can see that the effect on LFP is gradual.



It essentially means - +1C is not massively safer then -1C Zero is just random value chosen for familiarity.

Impact of Test Conditions While Screening Lithium-Ion Batteries for Capacity Degradation in Low Earth Orbit CubeSat Space Applications

A wide variety of commercial cylindrical lithium-ion batteries are available for use in nanosatellites (CubeSats) that cycle in low Earth orbit (LEO). This space application differs greatly from the conditions used to create the manufacturer datasheets that CubeSat teams rely on to screen cell...

www.mdpi.com

Fluorinated Solvent Molecule Tuning Enables Fast-Charging and Low-Temperature Lithium-Ion Batteries​

Yanbing Mo, Gaopan Liu, Yue Yin, Mingming Tao, Jiawei Chen, Yu Peng, Yonggang Wang, Yong Yang, Congxiao Wang, Xiaoli Dong, Yongyao Xia"

https://onlinelibrary.wiley.com/doi/10.1002/aenm.202301285

-20C is bad for Lithium - do not get me wrong - that will kill current chemistries pretty fast. But 0C is a rather arbitrary cutoff in my opinion.

Lets get the debate up and point out the flaws in my Thesis.

 

[sunshine_eggo]

Can be charged at temperature down to -20°C for cold weather use (sub Zero version)

Charging Your Lithium Battery Below Zero - DC Battery Technologies

How to correctly charge your Lithium Battery is a frequently asked question. By following this simple guide, you will have all the knowledge to look after your battery efficiently!

dcbattery.tech

Nope. It does NOT charge at -20°C, it's heated:

"The process of heating and charging is automatically controlled by the BMS and the heating element embedded within the battery and takes roughly 40 minutes to change the temperature from -20°C to +5°C. Once the battery temperature reaches +5°C the charging starts immediately and once the temperature rises to +10°C the heating element stops and continues with the charging."

-20C is bad for Lithium - do not get me wrong - that will kill current chemistries pretty fast.

Yttrium doping of the cathode can permit safe charging down to -20°C.

But 0C is a rather arbitrary cutoff in my opinion.

Agreed. The issue is that most manufacturer's don't publish charge rates at reduced temperatures, so everybody just says "don't charge below freezing.

 

[eXodus]

Yttrium doping of the cathode can permit safe charging down to -20°C.

interesting - are those common place in current consumer grade batteries?

Agreed. The issue is that most manufacturer's don't publish charge rates at reduced temperatures, so everybody just says "don't charge below freezing.

Yes, that was my point - and every review and youtube video are pointing that out.

Now we are getting batteries with 0C switches - which could be charged lower - but all youtuber ripping them to shreds in their videos and say - bad manufacturer bad bad no low temp cut-off.

While the low temp charging- answer is getting more nuanced.

 

[Hedges]

Here were some manufacturer tables with recommended max charge current vs. temperature.
Even above 0C, reduced charge rate is needed to avoid excessive deterioration.
Maybe very low rate is OK a bit below 0C, but only the Gangfen table allows it.

[Edit, forgot the link. As Sunshine says below, known here for a few years.]

Why you cannot charge LiFePO4 below 0 degrees Celsius

I am not an expert either but my understanding is: The simple answer is just don't charge under 32*F The complicated answer is... its complicated, but still no.. ;) There are a number of variables to consider with low temperature charging (1) temperature (2) C-rate (3) SOC (4) degree of...

diysolarforum.com

 

[sunshine_eggo]

interesting - are those common place in current consumer grade batteries?

No. IIRC, the premium Thundersky/Winston batteries from about 10 years ago did, but it seems very rare these days.

I use Panasonic NMC cells taken from plug in hybrids that spec unrestricted charging down to -20°C... but I still use my Batrium to prevent charging below 5°C because.

Yes, that was my point - and every review and youtube video are pointing that out.

Now we are getting batteries with 0C switches - which could be charged lower - but all youtuber ripping them to shreds in their videos and say - bad manufacturer bad bad no low temp cut-off.

Aren't they shredding them because they allow any charge current at any temperature? I'd say that deserves shredding.

While the low temp charging- answer is getting more nuanced.

This feels like a re-hash to me. The fact that it's a progressive taper has been common knowledge on this forum for at least three years.

 

[beckkl]

Just seeing this thread. Wondering what the though it is on charging Eve 304AH cells at say, .02C when below freezing. I just built a seplos DIY pack with the heaters, but it sounds like it doesn't preheat the batteries.

 

[SeaGal]

Just seeing this thread. Wondering what the though it is on charging Eve 304AH cells at say, .02C when below freezing. I just built a seplos DIY pack with the heaters, but it sounds like it doesn't preheat the batteries.

Here is the EVE charge profile for the LF280K cells - I suspect the 304Ah cells are not much different.

So, personally, I would not attempt to charge them much below +5C.

I thought the BMS's with heaters first direct solar generation to the heaters and only when the cell temp reaches your pre-defined temp would the BMS allow the cells to be charged?

Also see my posting here...

Science based discussion on charging LiFePO4 below 32°F

I am not sure if any BMS has more than 2 states, on and off. Besides… Isn’t this what charge controllers are designed to do (scale current): I am not sure I would want a more complex BMS as it would likely reduce reliability. And for the last line of defence, BMSs need more reliability if...

diysolarforum.com

 

[Ampster]

No worries for me. My soon to be installed Pytes V5 batteries have built in heaters.

 

[Lt.Dan]

I thought the BMS's with heaters first direct solar generation to the heaters and only when the cell temp reaches your pre-defined temp would the BMS allow the cells to be charged?

This is typically correct, and the preferred way to do it. But you can never trust consistency from manufacture to manufacture. One will have to reach out to the manufacturer to find out for sure.

 

[beckkl]

This is typically correct, and the preferred way to do it. But you can never trust consistency from manufacture to manufacture. One will have to reach out to the manufacturer to find out for sure.

Others with the seplos BMS have confirmed, there is no combination of parameters that can be entered in the BMS to allow it to heat without charging. This presents a unique problem for me, as my setup is in an unheated shed in an area that can get down to -20C at night during the winter. I think I am just going to have to make sure there is enough solar production to keep the heaters going and the batteries over 0deg. I'll likely wrap the entire seplos case in 2" of EPS insulation.

 

[SeaGal]

This presents a unique problem for me, as my setup is in an unheated shed in an area that can get down to -20C at night during the winter.

So presumably there is no grid power to keep them warm overnight? My DIY battery system has 2" of PIR insulation and just 21W of heaters keeps the 14.3kWh around 20C when it's -5C outside and they're only on 30% to 50% of the time.

 

[Lt.Dan]

Others with the seplos BMS have confirmed, there is no combination of parameters that can be entered in the BMS to allow it to heat without charging. This presents a unique problem for me, as my setup is in an unheated shed in an area that can get down to -20C at night during the winter. I think I am just going to have to make sure there is enough solar production to keep the heaters going and the batteries over 0deg. I'll likely wrap the entire seplos case in 2" of EPS insulation.

I don't know why you would want to waste power to heat all night when you aren't charging?

 

[beckkl]

I don't know why you would want to waste power to heat all night when you aren't charging?

Because in the morning I can't preheat the batteries before charging.

 

[Lt.Dan]

Because in the morning I can't preheat the batteries before charging.

Preheating the batteries shouldn't take more than 30-45 minutes, even if they are cold soaked to -20C. Getting them to 2-5C shouldn't take very long.

Like you said though, lots of insulation will really help with that also. Don't forget the batteries will slightly self heat, so with enough insulation, they will keep themselves warm enough.

 

[beckkl]

So presumably there is no grid power to keep them warm overnight? My DIY battery system has 2" of PIR insulation and just 21W of heaters keeps the 14.3kWh around 20C when it's -5C outside and they're only on 30% to 50% of the time.

Correct, it is an off-grid property. That is good to know about the efficiency of the insulation + heaters. I am hoping to need < 1KW a day to keep it heated, which sounds very doable.

Preheating the batteries shouldn't take more than 30-45 minutes, even if they are cold soaked to -20C. Getting them to 2-5C shouldn't take very long.

Like you said though, lots of insulation will really help with that also. Don't forget the batteries will slightly self heat, so with enough insulation, they will keep themselves warm enough.

See my previous comments. My current setup does not allow this (Seplos BMS with heating pads). There is no ability to heat the batteries without charging them.

 

[Lt.Dan]

See my previous comments. My current setup does not allow this (Seplos BMS with heating pads). There is no ability to heat the batteries without charging them.

I understand that. In the early morning when charge current is just starting to come up, you are loosing such a small amount of PV in that 30-45 minutes to heating, much less than if you heated the batteries ALL NIGHT, and insulating will make that time even shorter, or prevent it all together.

 

[HighDesertOffgrid]

Others with the seplos BMS have confirmed, there is no combination of parameters that can be entered in the BMS to allow it to heat without charging. This presents a unique problem for me, as my setup is in an unheated shed in an area that can get down to -20C at night during the winter. I think I am just going to have to make sure there is enough solar production to keep the heaters going and the batteries over 0deg. I'll likely wrap the entire seplos case in 2" of EPS insulation.

What is your current solution to this problem?
Edit: nevermind. I see you just built the pack.

 

[SeaGal]

you are loosing such a small amount of PV in that 30-45 minutes to heating

Do we know it would be that quick? I've not been in a situation to test it, but would assume that the specific heat capacity and density of 16 x EVE 304Ah cells would take quite some time to raise their internal temperature by +5C

 

[beckkl]

I understand that. In the early morning when charge current is just starting to come up, you are loosing such a small amount of PV in that 30-45 minutes to heating, much less than if you heated the batteries ALL NIGHT, and insulating will make that time even shorter, or prevent it all together.

Am I missing something? My concern is that early in the morning I will be charging frozen batteries for a time.

See this post:

Seplos heating function not working?

I’ve been chatting to a Seplos engineer to try and understand how to make this work, and according to what I’ve been said, this should work. I’ve placed temperature sensor 1 just above the heating pad, and temperature sensor 2 in a glass with ice Temp 2 is 3°, so it should activate heating...

diysolarforum.com

Which is my exact setup. It takes many hours to take the battery up 10deg C.

 

[Hedges]

Do we know it would be that quick? I've not been in a situation to test it, but would assume that the specific heat capacity and density of 16 x EVE 304Ah cells would take quite some time to raise their internal temperature by +5C

Or to lower it at night.

I'm not sure that maintaining battery temperature at night consumes much more than warming it back up in the morning. It is just a matter of that extra 5C delta T, and thermal resistance.

I'd think a few inches of foam would make heat loss negligibly low. For summer, need a manual or automatic vent opened.

While you're at it, raise not just 5 degrees but enough that the battery can comfortably accept the power you will have available. The curves for cold temperature charging dropped quite low, like 0.2C. I don't think many, if any, of you have charge current adjustable based on temperature.

 

[SeaGal]

I'd think a few inches of foam would make heat loss negligibly low. For summer, need a manual or automatic vent opened.

very low. It's funny but last summer, the 2" of PIR around the batteries stopped them heating up as much as the garage air temp got to in the sunny afternoons!

I don't think many, if any, of you have charge current adjustable based on temperature.

I do I have temperature and SOC mappings... see...

Science based discussion on charging LiFePO4 below 32°F

I am not sure if any BMS has more than 2 states, on and off. Besides… Isn’t this what charge controllers are designed to do (scale current): I am not sure I would want a more complex BMS as it would likely reduce reliability. And for the last line of defence, BMSs need more reliability if...

diysolarforum.com

 

[beckkl]

Or to lower it at night.

I'm not sure that maintaining battery temperature at night consumes much more than warming it back up in the morning. It is just a matter of that extra 5C delta T, and thermal resistance.

I'd think a few inches of foam would make heat loss negligibly low. For summer, need a manual or automatic vent opened.

While you're at it, raise not just 5 degrees but enough that the battery can comfortably accept the power you will have available. The curves for cold temperature charging dropped quite low, like 0.2C. I don't think many, if any, of you have charge current adjustable based on temperature.

I have solar assistant configured + home assistant, so can adjust the max charge amperage based on temp. But it is sort of irrelevant since I can't get above .1C with my current production.

 

[Lt.Dan]

I'm thinking in this early portion of the morning, here is a screen shot of mine this morning:


So if heating begins at 6:45am, or so, right when solar just starts to come in (ignoring my home load, just focus on PV Charging the battery), the battery will begin heating because it detects charge current, then by 7:30 (maybe much sooner, depending on Cell temp, and insulation), the battery is warm, and ready to accept the 1kw of solar that is coming in. In that 45 minutes, you've lost maybe 4-500wh of possible solar, because it was only letting the heaters run, and not allowing any other charge current.

And by that time, if it starts charging the battery with a full 1kw, at 7:30am, and say you have a 100ah battery bank (abnormally small, but exaggerated for the example), then you are still only charging at .2C rate. If you have a 280ah bank, which I would consider minimum for a 48v bank, then its only a 0.07C rate. Should be no problem for a LiFePO4 battery at 2-5*C.

Another thing that popped into my head, is what if you don't have good sun in the morning/next day? You heated that battery all night to keep it ready for the next day, and wasted that energy because there is no charging the next day. PV might not even cover your loads, so its definitely not charging the battery. Now you lost that energy you could have used during the day because it was wasted in the night to heat.

 

[beckkl]

I'm starting to question if you are reading my replies carefully. The example you provide is not reproducible with a Seplos BMS. You cannot "let the heaters run, and not allow any other charge current". The BMS does not allow for this to happen. There is simply no settings in the BMS that will allow you to have the heaters on and the cells not accepting a charge with a Seplos BMS.

If you don't keep the batteries above 0 deg C you have no choice but to charge the cells below 0deg C, at least until the heaters get them over 0deg C which can be several hours based on others who have tested this exact scenario. Which is why I originally asked what the impact of charging at an extremely low C rate might be.

 

[Lt.Dan]

I'm starting to question if you are reading my replies carefully. The example you provide is not reproducible with a Seplos BMS. You cannot "let the heaters run, and not allow any other charge current". The BMS does not allow for this to happen. There is simply no settings in the BMS that will allow you to have the heaters on and the cells not accepting a charge with a Seplos BMS.

If you don't keep the batteries above 0 deg C you have no choice but to charge the cells below 0deg C, at least until the heaters get them over 0deg C which can be several hours based on others who have tested this exact scenario. Which is why I originally asked what the impact of charging at an extremely low C rate might be.

My apologies, I assumed the Seplos activated the heaters in the manner that @SeaGal mentioned on post #7. If the Seplos BMS does not switch off the charge mosfets, and allow the heaters, then it is pretty worthless if you ask me. Maybe reach out to Seplos and ask for a firmware update? It should be capable of such with the current hardware if I remember correclty.