Is My Battery Toast?

[MisterSandals]

sorry you are right

No need to be sorry, your English is MUCH better than my second language!

I was mostly curious as to what effect you are referring to so i can look it up and maybe learn something today!

I did learn a new word today (snobbler) and i am looking forward to my first opportunity to use it in conversation.

 

[Northernchateau]

440W X 3 in parallel. The Growatt often throws a high bus voltage error on sunny days, even after adding a switch to remove 1 of the panels from the array on sunny days (but I use all 3 on cloudy/overcast).

Panels in Parallel configuration, the voltage does not add together just the current does.
Adding or taking away panels of the same brand and wattage will not change the output voltage.
Please post a pic of the lable on your panel and what brand/model SCC are you running?

 

[lexio]

mr snoobler was saying everybody is lying some what so -10% of the capacity of the battery is normal.
Some thing like that sorry cant find the original text.



but if i see my system in my rv with a compressor fridge some led lights water pump charge phone radio inverter ( non all in one ) and so on i use almost 1.5 kwh

have a 320 w solar flat on my rv witch gives me on a good day maybe 200 watt

 

[robby]

mr snoobler was saying everybody is lying some what so -10% of the capacity of the battery is normal.
Some thing like that sorry cant find the original text.



but if i see my system in my rv with a compressor fridge some led lights water pump charge phone radio inverter ( non all in one ) and so on i use almost 1.5 kwh

have a 320 w solar flat on my rv witch gives me on a good day maybe 200 watt

I always admire people who can speak and write in a second language, but I am utterly amazed by those who can pull it off while talking about technical topics.
Very few people can do that.

 

[Mattb4]

Your batteries are evidently charging and discharging. Whether they have the capacity that they are rated for is an open question. Only way to know for certain is to do a load test. The best way to do that is to fully charge your batteries (such that the resting voltage reads 27.2v for a 24v (8s) LiFePO4 battery.) before running a test.

If your batteries have the indicated capacity, and they deplete faster than you expect, the next area of testing is to find your actual loads.

Final issue is your soalr panel and AIO setup. From your description something is not right that you need to switch out a panel during Summer.

 

[Goboatingnow]

Unlikely to damage the cells, but the bms could fail from frequent high voltage disconnect.
A cell can reach 100%SOC at 3.4V, but it can safely reach 3.65 without damage.
If the bms is working, 28.4 shouldn't hurt the cells.

If the bms did not do HVC disconnect that float voltage left for any amount of time would definitely damage the cells with plating effects SEI layer growth

Is your battery toast? Possibly

 

[rykelo]

I would lower the float to 27.6V
Ok to keep absorb at 28.4, however some out of balance cells can still trigger overvoltage.
The overvoltage likely is due to the bms limiting charging.
You need a larger bank, or additional load to keep the battery from

Thanks, I've lowered Fv to 27.6V

 

[rykelo]

How did you figure that is was 80% charged? By voltage from the inverter while under load?
What is the idle draw from the Growatt?
How much power does your refrigerator and LED lights use "by the next day"?

I suspect you might be reading too much into surface charge, assuming that 28.4V is 100%. The surface charge may be less than 1% of total capacity and you could still be virtually at 100% when voltage is around 27V-27.5V.

I got my "80% charged" by just seeing what the Growatt was showing for the battery voltage (26.6V) under no loads. Under no loads, having it show 26.6V and then 26.1V 12 hours later (Growatt was turned off) is how I'm concluding that my battery is having problems. Guys, assume I know nothing about batteries. Total beginner. I bought this battery from a local solar outfit, they built it. It appears to have BMS wired in but to be honest, I barely understand what a BMS does (other than try to keep the PV from destroying the battery). My BMS doesn't appear to communicate with the Growatt, nor do I know how to get individual cell readings (or what to do if I were to discover a cell was low).

At this point, I'm just trying to figure out my best option for keeping my lights on and food cold next season... limp along with what I have, or buy a new battery bank ?

 

[MisterSandals]

Under no loads, having it show 26.6V and then 26.1V 12 hours later (Growatt was turned off) is how I'm concluding that my battery is having problems.

I guess this assumes there is no draw even when off. Maybe someone with this unit can confirm?

I barely understand what a BMS does (other than try to keep the PV from destroying the battery)

Yep, its a cutoff switch. It has wires to each cell pair (more on this later).

nor do I know how to get individual cell readings

If you have a volt meter, its super easy since you have access to all the cell posts.
From your pic, its apparent that you have 80Ah cells paired up (2P) to make a "120Ah cell equivalent". Each cell in the pair will have identical voltage because they are connected but one may be propping the other up. The voltage should be around 3.2V (its nominal voltage which is about 80% charged).
It takes 8 cells (or cell pairs in your case) in series (which sums the voltages) to make a "24V" battery (25.6V nominal (8 x 3.2V)).

If you can test the 8 cell pair voltages (pictured below), its possible to see if there is a bad cell pair (the most common trait of a failing battery). And yes, cell 1 is the negative end of the battery, so cell 8 the positive end.

 

[Goboatingnow]

I guess this assumes there is no draw even when off. Maybe someone with this unit can confirm?


Yep, its a cutoff switch. It has wires to each cell pair (more on this later).


If you have a volt meter, its super easy since you have access to all the cell posts.
From your pic, its apparent that you have 80Ah cells paired up (2P) to make a "120Ah cell equivalent". Each cell in the pair will have identical voltage because they are connected but one may be propping the other up. The voltage should be around 3.2V (its nominal voltage which is about 80% charged).
It takes 8 cells (or cell pairs in your case) in series (which sums the voltages) to make a "24V" battery (25.6V nominal (8 x 3.2V)).

If you can test the 8 cell pair voltages (pictured below), its possible to see if there is a bad cell pair (the most common trait of a failing battery). And yes, cell 1 is the negative end of the battery, so cell 8 the positive end.
View attachment 119532

You have achieved two things

Probably you have severe cell imbalance which effectively delivers lower then plated capacity

The high float has lead to internal plating , SEI layer growth and other degradation internally these again present as loss of capacity.

It may not be recoverable if this charge cycle has being going in for some time. Measure each cell with a good multimeter

Get rid of float voltages. Lithium should nit be subject to float voltages at all preferably.