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

[john61ct]

Originally Posted by newhaul

Apparently charging our lfp banks at sub freezing temps is not a problem when charging at sub.3C rates.

At least according to battleborn CEO Denis Phares.

As long as not **too** far below, but me, that low I'd stay under 0.1C, or pre-warm the bank.

Like so many issues, hard to nail down hard numbers when the damage done is lost cycles off the back end.

Actual now-noticeable damage, and certainly rendering the bank instant scrap, only happens long past the point where longevity was being reduced.

Most of the recent research studies show the effect very clearly without destroying the cells, but

each chemistry, each model battery will have different numbers.

Only the minimum "no charging anywhere near this temp or instant scrap" spec is on the data sheet.

In truth you usually can charge at a low C-rate around 0°C

But in general, being conservative I'd start pre-warming below 10° if going over 0.1C

25° should be fine for 0.2-3C

Faster charging than this, anybody's guess, impossible to detect the factors leading to lost lifecycles without forensic autopsy, studies show different numbers for even slightly different chemistries.

So for 0.5C and above, I'd go to 30° first to maximize longevity.

Of course in many contexts people just take the hit, if they're even aware of the issue.

[john61ct]

And for those inclined to take Winston Chung's word, apparently his Yttrium doping allows for charging at much lower temps, and at higher rates in "cooler" temps.

But all that was long before the imaging-based studies came out, might be based only on "immediate gross" damage rather than just sacrificing lifetime cycles.

[newhaul]

Originally Posted by john61ct

As long as not **too** far below, but me, that low I'd stay under 0.1C, or pre-warm the bank.

Like so many issues, hard to nail down hard numbers when the damage done is lost cycles off the back end.

Actual now-noticeable damage, and certainly rendering the bank instant scrap, only happens long past the point where longevity was being reduced.

Most of the recent research studies show the effect very clearly without destroying the cells, but

each chemistry, each model battery will have different numbers.

Only the minimum "no charging anywhere near this temp or instant scrap" spec is on the data sheet.

In truth you usually can charge at a low C-rate around 0°C

But in general, being conservative I'd start pre-warming below 10° if going over 0.1C

25° should be fine for 0.2-3C

Faster charging than this, anybody's guess, impossible to detect the factors leading to lost lifecycles without forensic autopsy, studies show different numbers for even slightly different chemistries.

So for 0.5C and above, I'd go to 30° first to maximize longevity.

Of course in many contexts people just take the hit, if they're even aware of the issue.

Sorry but i would have to take Denis Phares word over your word he has skin in the game and has to honor his company warranty.

[newhaul]

Originally Posted by john61ct

As long as not **too** far below, but me, that low I'd stay under 0.1C, or pre-warm the bank.

Like so many issues, hard to nail down hard numbers when the damage done is lost cycles off the back end.

Actual now-noticeable damage, and certainly rendering the bank instant scrap, only happens long past the point where longevity was being reduced.

Most of the recent research studies show the effect very clearly without destroying the cells, but

each chemistry, each model battery will have different numbers.

Only the minimum "no charging anywhere near this temp or instant scrap" spec is on the data sheet.

In truth you usually can charge at a low C-rate around 0°C

But in general, being conservative I'd start pre-warming below 10° if going over 0.1C

25° should be fine for 0.2-3C

Faster charging than this, anybody's guess, impossible to detect the factors leading to lost lifecycles without forensic autopsy, studies show different numbers for even slightly different chemistries.

So for 0.5C and above, I'd go to 30° first to maximize longevity.

Of course in many contexts people just take the hit, if they're even aware of the issue.

you really need to be specific as to what you are referring to .
30℃ is 86℉
At 86℉ you are getting toward the warm top end for high rate charging .

[newhaul]

Originally Posted by john61ct

And for those inclined to take Winston Chung's word, apparently his Yttrium doping allows for charging at much lower temps, and at higher rates in "cooler" temps.

But all that was long before the imaging-based studies came out, might be based only on "immediate gross" damage rather than just sacrificing lifetime cycles.

as with Denis I would take their word they have skin in the game .

[john61ct]

While not doing damage discharging in cold temps at House bank rates is greatly impaired.

At propulsion C rates, damage can be done too far below freezing with discharging as well. That has not yet been rigorously researched, but at least for non-LFP chemistries is well known from observation among EV / eBike and RC communities.

Amazing how much capacity and power output is reduced even before going below freezing.

[newhaul]

Originally Posted by john61ct

While not doing damage discharging in cold temps at House bank rates is greatly impaired.

At propulsion C rates, damage can be done too far below freezing with discharging as well. That has not yet been rigorously researched, but at least for non-LFP chemistries is well known from observation among EV / eBike and RC communities.

Amazing how much capacity and power output is reduced even before going below freezing.Attachment 206366

its also must be amazing that all batteries suffer capacity loss with declining temperatures.

Now my real question on all of this sub freezing charging . How many of us that are using Lfp house banks are actually worried about charging the banks with said bank having a temperature below freezing. 0℃ or 32℉ .
The water I sit in is rarely below 45℉ at surface . And I have never seen frozen fresh water in my bilge / engine room where most banks are mounted. Inside my boat it is rarely below 50℉ and not below 65℉ when I'm aboard .

If your bank is below freezing I'm sure you are not on the boat and it is on the hard in winter layup. So no charging is happening anyway.

[john61ct]

All Celsius, as specified in the first.

And no, very common for use cases that need really fast C-rate charging to heat the cells up to very high temperatures

but just for the charging, not storage or discharge.

Obviously they're not as concerned about maximizing longevity, and no one knows where the balance point is, just too many variables.

But even for House bank use, if I wanted to charge at say 1.5C or higher, heating the cells up to well over 35°C would IMO be better than leaving them below say 25°.

[john61ct]

All temps are **cell** temps, ambient plays a role of course but there's a thermal mass lag effect.

Have yet to see bare cells with embedded sensor leads, but I bet we will in coming years.

Relion sells LFP with internal cell heating now.

http://www.sci-news.com/otherscience...ery-07777.html

[newhaul]

Originally Posted by john61ct

All Celsius, as specified in the first.

And no, very common for use cases that need really fast C-rate charging to heat the cells up to very high temperatures

but just for the charging, not storage or discharge.

Obviously they're not as concerned about maximizing longevity, and no one knows where the balance point is, just too many variables.

But even for House bank use, if I wanted to charge at say 1.5C or higher, heating the cells up to well over 35°C would IMO be better than leaving them below say 25°.

1.5C. I have never seen a small boat like we all have ( ie: under 100' )
having enough charging capability to charge our banks at that high of a rate.
For example I will soon have 240ah Lfp there is no where to mount enough charging capacity to charge at 320 amps not to mention where would you get that much power to support that much charge.
And I'm a small bank.
Lets keep it applicable to our use case shall we.

[john61ct]

Nope some aren't so limited.

Just saying no need to be so cautious about temps higher than we've considered in the past, if you have a compelling reason to fast charge.

[john61ct]

Imaging dendrite formation

https://streamable.com/rksrw

[newhaul]

Originally Posted by john61ct

Nope some aren't so limited.

Just saying no need to be so cautious about temps higher than we've considered in the past, if you have a compelling reason to fast charge.

by not limited what or who are you referring to?

Please show an example of a cruiser that we may know that is using Lfp and charging at even 1C . Not that it is possible but that is actually doing it .
What is their boat size, bank size , and charging ability . ( verifiable not theoretical)
after all this thread is geared toward those of us actually using Lfp house banks.
( in other words this thread is literal not theoretical.)

[newhaul]

Originally Posted by john61ct

Imaging dendrite formation

https://streamable.com/rksrw

we have all seen this one a long time ago.

[CatNewBee]

Originally Posted by john61ct

All Celsius, as specified in the first.

And no, very common for use cases that need really fast C-rate charging to heat the cells up to very high temperatures

but just for the charging, not storage or discharge.

Obviously they're not as concerned about maximizing longevity, and no one knows where the balance point is, just too many variables.

But even for House bank use, if I wanted to charge at say 1.5C or higher, heating the cells up to well over 35°C would IMO be better than leaving them below say 25°.

35°C can reduce capacity, heat is worse than low temperatures