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...

[S_Davis]

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%.

[Itinerant1]

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.

What charge voltage do you recommend? What are you calling 100% charge...voltage? Is that 100% and using it? 100% then resting it? Oh so many more questions I could think of as a daily user and charging to 14.1v almost everyday when the sun permits it, am I killing the batteries or shortening their life? Should we be using batteries for longevity or daily loads?

[pianotuna]

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.

[TechWriter]

S Davis wrote:

I have four lightly used Trojan T-105s I can’t find a home for.

Now you tell me.

[TechWriter]

wa8yxm wrote:
TecWriter said:"Get on youtube and you will see the extra ordinary measures needed to destroy an LFP cell."

I see many things on You Tube that are ...... Well...... Entainertaining yes. Factual no.

Um, that was time2roll, w8forit, not me.

The YouTube link I gave was to someone who seems to know what he’s talking about. That’s why I’m pretty sure you didn’t check it out.

[jaycocreek]

wa8yxm wrote:
FOr me there is now (Was not when I was in the motor home) another advantage to LI and one less disadvantage

The advantage is LBS. the LI's don't have as many LBS to lug up the stairs to my battery box.

The no longer a disadvantage is Degrees (F or C) LI's don't like to charge at LOW temp.. NOT a problem here INSIDE the apartment.

Reason why I'm considering LI's (not ready to change yet) for my E-power/12 volt system .. yes I have a 12 volt system in the apartment. also multiple 2-way 12 volt powered radios. fans. Even lights.

I did my lfp with home use in mind..Each battery and inverter can easily be carried inside to run inside appliances/internet/cpap etc rather than totally attached to an RV,with two of them in battery boxes with all the extras and the other in a soft cooler...

I never thought I would go this route after years of wet cell batteries without any issue...The way the world is now,I'm glad I went this route..

[wa8yxm]

FOr me there is now (Was not when I was in the motor home) another advantage to LI and one less disadvantage

The advantage is LBS. the LI's don't have as many LBS to lug up the stairs to my battery box.

The no longer a disadvantage is Degrees (F or C) LI's don't like to charge at LOW temp.. NOT a problem here INSIDE the apartment.

Reason why I'm considering LI's (not ready to change yet) for my E-power/12 volt system .. yes I have a 12 volt system in the apartment. also multiple 2-way 12 volt powered radios. fans. Even lights.

[S_Davis]

RLS7201 wrote:
Every time I see a thread like this, I go give my 6 volt, wet cell, GC batteries a hug. No BMS. No DC to DC charge to protect my alternator. No worries about ambient temperature.
The draw back is having to check the water levels twice a year.

Sent from my flip phone.............

Richard

I have four lightly used Trojan T-105s I can’t find a home for.

[S_Davis]

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, oh and the weight I have 500ah of usable capacity at a little over 110lbs.

[3_tons]

RLS7201 wrote:
Every time I see a thread like this, I go give my 6 volt, wet cell, GC batteries a hug. No BMS. No DC to DC charge to protect my alternator. No worries about ambient temperature.
The draw back is having to check the water levels twice a year.

Sent from my flip phone.............

Richard

I use to feel the pretty much the same way about my sixers - that is until a twist of fate intervened - lol.

I got the opportunity (donated spare time and labor) to fully convert a friends V-nose cargo trailer into a ‘full fledged’ camper, with 400w of MPPT solar, Aims pure-sine pass-thru inverter-charger, air conditioner, Danfoss compressor refer, shower (50 gal fresh), and even a SCR rectifier-based diversion-load hot water heater…He insisted on going with a single 100a/h Aims LFP (later upgraded to two, and 800w solar…).

During the course of this build (which took about 3 or so mos), I was afforded (by being alone, 🙂 he-he!) pretty much a cart blanc opportunity to assemble, test (actually torture test!!) this ‘weird’ LFP under all kinds of loads, incl. heavy inductive, and (relative to my two GC’s) it’s rapid harvest recovery…Ran the 11kbtu air conditioner a bunch, and on one occasion inadvertently noticed that the LFP had gotten to an amazing 6% SOC (per Victron BMV shunt meter), compressor running!…On another occasion I strung together a full 100’ extension cord to reach over to my garaged camper (from his LF 2500w Inverter) and it ran my air conditioner without a hitch!…After awhile it began to occur to me that for the most part SOC was pretty much a non-issue (due to a relatively flat voltage profile), and that a full charge was mostly unimportant and after this period of exposure, with many free-lance exhaustive trials (some covert!), I felt forced to cave and made the leap into ‘(or back to?) the future’ lol…

In closing, the best way I can relate the difference (via arguably, just analogy) is to say, similar to comparing grid power to GC battery power…I would also add that while a BMS may be a concern for some, charging is far simpler simply because (assuming solar?), staying anywhere’s within say the middle ground of SOC span is plenty good enough, and because of this, charging is much less frequent due to LFP’s far deeper depth of discharge and extent of usable SOC.

Either way, Just don’t ask me anything about pregnancy, because fortunately I’m unable to ever experience it - lol

3 tons

[RLS7201]

Every time I see a thread like this, I go give my 6 volt, wet cell, GC batteries a hug. No BMS. No DC to DC charge to protect my alternator. No worries about ambient temperature.
The draw back is having to check the water levels twice a year.

Sent from my flip phone.............

Richard

[3_tons]

This has been a good thread…I should add to my previous (for those not as electrically inclined…) that warranties are only as good as the supplier-vendor, and your proximity to them…Cost from a reputable North American supplier may initially be somewhat higher (QC, and often cylindrical cell quality as well…), but over time something worthy of consideration, and possibly with far less aggravation in the end…JMHO

3 tons

[S_Davis]

I ended up building my own but I am an HVAC/Electrical contractor with over 30 years in the trades. If buying off the shelf I would make sure the battery is serviceable, no welded buss bars and you could take all the connections apart to service/replace them or the BMS.

The cells could last 15-20 years BMS and terminal connections not so much, if the warranty Is done or the company is out of business you at least have an option of repair.

[3_tons]

wa8yxm said: “Someone mentioned LiFePO4 batteries with REPLACEABLE BMS systems.

I do not recall mention of brands or links to them..
Can said someone supply?”

I did allude to this feature, but not meant in the sense of ‘user replaceable’, and I’ve only seen this on a few of the higher end (e.g. costlier) LFP’s… Not sure about BattleBorn, but Viper and Aims comes to mind…And coincidentally (by correlation??) these tend to be batteries having longer warranties….JMO, Sorry for any unintended confusion…

3 tons

[wa8yxm]

TecWriter said:"Get on youtube and you will see the extra ordinary measures needed to destroy an LFP cell."

I see many things on You Tube that are ...... Well...... Entainertaining yes. Factual no. But I do suspect the LiFePO4 types are safe. and I do use one with no special protection. (Small one 12 AH)

****

Someone mentioned LiFePO4 batteries with REPLACEABLE BMS systems.

I do not recall mention of brands or links to them..
Can said someone supply?