Not the cells that fail it is the battery Management System!

[pianotuna]

Hi all,

"The Weak Link - The BMS

We now have a few years of experience with lithium-ion batteries, and what is becoming clear is that while the LiFePO4 cells hold up very well, that is not the case with the Battery Management System (BMS). Overall the number of prematurely failed batteries is small, but with 10,000+ batteries sold it is clear that in 99% of cases it is the BMS that fails, turning the battery into an expensive piece of gender-neutral-cave decoration!

While we very much advocate for using batteries with a build-in BMS (without one the battery would be unsafe and likely fail very quickly!), manufacturers struggle to make their BMS as bullet-proof as it should and needs to be. Surge currents due to the input capacitors of large inverters, motors, and air-conditioners can and at times will kill the BMS, rendering the battery useless.

At least one well-known battery manufacturer is now enforcing their warranty conditions to the letter, and that requires the use of an external current limiter when their batteries are used with large inverters (“large” being defined as 3,500 Watt and up). This leads to the ironical situation where the BMS is there to protect the battery, and now a current limiter gets connected to protect the BMS. What will be next to protect the current limiter…

Seeing how the BMS has become the weak link, manufacturers should really work (hard) on hardening that. Nothing is 100% bomb-proof, but there certainly is room for improvement! Another solution could be to acknowledge that the BMS is the weak link and make it so it can be replaced without too much effort, for example a gasketed lid on the battery that is removable with a few screws, and a BMS that has connectors and bolted lugs, so a repair shop can swap the board. It makes no sense to throw away a battery where 90% of the cost is in the cells, and 10% in the BMS, just because the BMS failed."

From:

https://www.solacity.com/how-to-keep-lifepo4-lithium-ion-batteries-happy/?fbclid=IwAR0FAHVnbdaMhMmT3...

[Y-Guy]

And we’re done. Closing the tread for a time out.

[3_tons]

“ I really have no horse in the race.”

Yet we still haven’t heard what your purported “Li device” is??…Please provide details :)…

3 tons

[Itinerant1]

Today makes 6 years of continuous use of my system with lfp of fulltime boondocking and the days that I was on a power pole I would turnoff the charging from inverter and let the power pass through so only solar was charging the the batteries if needed it from misc 12v loads (fridge, furnace).

2016_ 200 of 261 days
2017_ 365 of 365 days
2018_ 365 of 365 days
2019_ 344 of 365 days
2020_ 282 of 365 days
2021_ 349 of 365 days
2022_ 102 of 102 days

Total of 2,007 days boondocking.

Everyday there are high draw appliances being used from 5-20 minutes (coffeemaker, microwave) to 2-3 hours (15k air conditioner) or just the idle draw of the inverter with a humidifier always going 24/ 7 of 7ah. We live off of the system almost like being on the grid.

My solar and inverter/ charger are set to the same settings of 14.1v absorb (10 minute max, 6 minutes is the normal time till it switches to float), 13.6v float. Our daily power consumption can range from 175ah to 275ah just depending on the season. Shorter the day light hours the more power consumed from batteries. This is running everything in the trailer (not at once). Coffeemaker, microwave, air conditioner, vacuum, ice maker, fridge, air compressor, and other misc hand tools. My inverter is set to 12.0v cut off and never have had it shut down yet due to low voltage even when drawing 150a load at 30% SOC for 5 minutes.

If I have lost capacity I can not tell yet in my day to day use of the system. I have/ do use between 20-100% depending on the season.
I have not had to break the system apart for rebalancing of cells but had to replace 2 senseboards on 2 cells a couple years back. The cpu/ bms shut my batteries down and after bypassing the cpu/ bms was back up and running. Ran it like that for 2 months till I got south to replace them.

I guess my point being is that there are not alot of folks using their rvs in an extreme boondocking/ dry camping situation and try to get "longevity" out of the batteries seems just silly when using them per the manufacturer specs of voltage range 2.8vpc-3.65vpc should yeild a very long life of 2,000-5,000 cycles of 100% use seeing that most are just weekend worriors or on power poles most of the time and in those cases just get dead lead. I believe most will kill their lfp by mistakes of human error or the cells will age out.

Just my opinion from years of hands on experience in all environmental conditions and use and expect to get many more years out of the system.

[StirCrazy]

pianotuna wrote:

StirCrazy wrote:

pianotuna wrote:
Stir crazy,

I have no way of knowing what the battery chemistry is. It is not specified in the owners manual.

I'm only providing information for others. LiFePo4 are useless for me.

I believe they are wonderful batteries for temperatures above freezing.

so your providing information for other on somthing you have not used or don't know if you used, and yet the information you like to provide is from older chemestry lightium batteries which don't share the same properties as newer versions.... just think about that for a second...

Old? Nope just got it 2 weeks ago. Recommended 85% max charge for long life. I do read manuals and follow the recommendations.

What I don't know is the exact type of li battery.

if you just got it they do put the chemistry type in the owners manual nd it is written on the battery. so realy theres no excuse for you not to know.

nobody is disputing that if you use less of the capacity you get more life. this happens with every battery chemistry out there, flooded , agm, Si02, and Li. but they do have there rated life and at 3000 to 4000 cycles at 100% discharge are you worried about getting more cycles. when I sized my camper I used to have 110 usable AH in it with two 6v batteries, now I have 300AH so to use the full capacity would be a strech as the solare would charge long before I ever got that low. (I could go 3 days with out sun with the old batteries) so will I use all the battery, no i set my cut off to 11.9V so I am not using the bottom 8ish % and I'll probably only charge to 100% when I am actualy camping. I can change that setting in about 30 seconds with my phone. so maybe on the day I go home I'll set the charge limit to about 70% for storage and a day or two before I go camping Ill set it for 100% or heck I could use 90% that will still give me about 250 usable AH, thats the beautiful thing about sizing a battery properly, if gives you options and reserve capacity. so by using say 82% of my battery I could maybe get 7000 cycles instead of the 3500.. is that my concern? naw Ill be dead by the time I would ever use 7000 cycles, maybe I can leave this pack to my kids in the will...:B

[pianotuna]

StirCrazy wrote:

pianotuna wrote:
Stir crazy,

I have no way of knowing what the battery chemistry is. It is not specified in the owners manual.

I'm only providing information for others. LiFePo4 are useless for me.

I believe they are wonderful batteries for temperatures above freezing.

so your providing information for other on somthing you have not used or don't know if you used, and yet the information you like to provide is from older chemestry lightium batteries which don't share the same properties as newer versions.... just think about that for a second...

Old? Nope just got it 2 weeks ago. Recommended 85% max charge for long life. I do read manuals and follow the recommendations.

What I don't know is the exact type of li battery.

[StirCrazy]

pianotuna wrote:
Stir crazy,

I have no way of knowing what the battery chemistry is. It is not specified in the owners manual.

I'm only providing information for others. LiFePo4 are useless for me.

I believe they are wonderful batteries for temperatures above freezing.

so your providing information for other on somthing you have not used or don't know if you used, and yet the information you like to provide is from older chemestry lightium batteries which don't share the same properties as newer versions.... just think about that for a second...


as for tempatrue outside temprature has absolutly nothing to do with useing or charging LiFePO4 batteries, it is the battery temprature that matters, they are no use to you becasue ou refuse to put them in a conditioned space or use a heating system for them. for others who camp at -40 they might just be fine.

It just seams to me that because you don't want to put in the work to make them suitable, which is fine, you think that nobody should find them suitable and spread half truths or total BS about them in your never ending attack posts..

I have one of my rv's set up on LFP now and I think its wonderfull, and I would have no issue of camping at -35 except my old small furnace wouldnt keep up and theres hardly any insulation in the camper :B when I do up the 5th wheel that will be the test as I will camp in -15 to -20 in that if I have to.

[pianotuna]

Stir crazy,

I have no way of knowing what the battery chemistry is. It is not specified in the owners manual.

I'm only providing information for others. LiFePo4 are useless for me.

I believe they are wonderful batteries for temperatures above freezing.

[3_tons]

pianotuna wrote:
Hi 3tons,

I do have an li battery device. They happen to recommend 85% maximum charge to extend the life of the battery.

That’s good to know, but ‘service application’ matters (say, appliance, RV or what??) which will dictate both chemistry and charging requirements, right??.… Bottom line is ‘Li’ does not specifically denote LiFePO4 chemistry (nor do we know it’s a/hr capacity, or type of charging device?)…For clarity’s sake (meaning confusion avoidance) there’s no reason why a LiFePO4 cannot be fully charged - it’s just that it’s seldom necessary, and I suspect that (say, after one’s gained some hands-on familiarity and understanding - e.g. NOT of the Flooded Lead Acid type!…), few will commit to do so on a routine basis…

3 tons

[time2roll]

3 tons wrote:
This is where a few ‘determined’ FLA folks, unable to wrap their minds around LFP, inoculate themselves from empirical reality…

Yes and all the while cranking on the FLA at max voltage and amps as if it does not matter too.

[pianotuna]

Hi 3tons,

I do have an li battery device. They happen to recommend 85% maximum charge to extend the life of the battery.

[3_tons]

pianotuna wrote:

S Davis wrote:

pianotuna wrote:

S Davis wrote:
The thing I like is they will take every amp I throw at them until fully charged unlike other chemistries that charge slower at the top

Except that 100% state of charge is NOT a goal for li.

I didn’t say 100% state of charge, i said fully charged. Maybe I consider mine fully charged at 90%.

You may wish to consider 85% instead of 90% if you want maximum cycles.

It doesn't matter to me as Li are not in my temperature zone.

Well, here’s where actual user application and seasoned experience kinda, sorta matters - For instance, IF 85% is better than 90, then should we also assume that 80% is better than 85, and so on …(ad nauseam…)…One would like to think that this point is rather self evident, but from my perspective, what’s being ‘implied’ per caveat (while avoiding the explicit) is that a LFP ought not be fully charged (do so at your own RISK!!), and this is in fact patently False…But haven’t we seen this tactic elsewhere before?? (I’m starting to wonder, was this the design behind this thread??) - sadly, seasoned LFP posters have witnessed this pattern here before!)…And this is precisely how mythologies get launched (and re-launched!), to grow ‘plausable’ legs…

So say of the 3,000 to 5,000 cycles LFP’s are ostensibly capable of delivering (say with competent charging), does anyone worry about how many cycles will be lost by charging to a what I’d call a mere 90% versus 85?….Really??

This is where a few ‘determined’ FLA folks, unable to wrap their minds around LFP, inoculate themselves from empirical reality…

3 tons

[S_Davis]

pianotuna wrote:

S Davis wrote:

pianotuna wrote:

S Davis wrote:
The thing I like is they will take every amp I throw at them until fully charged unlike other chemistries that charge slower at the top

Except that 100% state of charge is NOT a goal for li.

I didn’t say 100% state of charge, i said fully charged. Maybe I consider mine fully charged at 90%.

You may wish to consider 85% instead of 90% if you want maximum cycles.

It doesn't matter to me as Li are not in my temperature zone.

The manufacturer specs are 10% to 90% SOC for 3500 cycles, that is in a compression fixture.

[pianotuna]

S Davis wrote:

pianotuna wrote:

S Davis wrote:
The thing I like is they will take every amp I throw at them until fully charged unlike other chemistries that charge slower at the top

Except that 100% state of charge is NOT a goal for li.

I didn’t say 100% state of charge, i said fully charged. Maybe I consider mine fully charged at 90%.

You may wish to consider 85% instead of 90% if you want maximum cycles.

It doesn't matter to me as Li are not in my temperature zone.

[3_tons]

pianotuna wrote:

S Davis wrote:
The thing I like is they will take every amp I throw at them until fully charged unlike other chemistries that charge slower at the top

Except that 100% state of charge is NOT a goal for li.

As I previously stated, ‘Discernment Required’ - gotta separate the chafe from the wheat…

3 tons