Signature Solar unbalanced!

[underdog5004]

Reviewing the thread found a couple things:

1. Apparently, anything over 40mv (not 400mv) is considered imbalanced. @SignatureSolarJess why werent my batteries showing higher than 40mv diff covered under warranty?

2. @EG4TechSolutionsTeam you suggested discharging at 0.5c until undervoltage protection was engaged. According to BMS-test, UVP engages at 40v pack voltage, or 2.5vpc. Is it safe to bring my cells this low?

 

[fnnwizard]

Reviewing the thread found a couple things:

1. Apparently, anything over 40mv (not 400mv) is considered imbalanced. @SignatureSolarJess why werent my batteries showing higher than 40mv diff covered under warranty?

This depends on where te cell Vs are with .040V delta.

If lowest cell is > 3.45V with low current charging, you're good. If lowest cell is < 3.42V, then likely no, but also dependent on ending charge current.

2. @EG4TechSolutionsTeam you suggested discharging at 0.5c until undervoltage protection was engaged. According to BMS-test, UVP engages at 40v pack voltage, or 2.5vpc. Is it safe to bring my cells this low?

At .5C rate, taking it to 2.5V/ cell is ok. You'll see it drops precipitously as it goes below 3.00V and there won't be much capacity to get to pack UVP... However, there is also cell UVP and that will get to its uVp sooner so capacity will be less..

That's why i asked above what the Vs were on the low end with the discharge current applied.

 

[underdog5004]

This depends on where te cell Vs are with .040V delta.

If lowest cell is > 3.45V with low current charging, you're good. If lowest cell is < 3.42V, then likely no, but also dependent on ending charge current.




At .5C rate, taking it to 2.5V/ cell is ok. You'll see it drops precipitously as it goes below 3.00V and there won't be much capacity to get to pack UVP... However, there is also cell UVP and that will get to its uVp sooner so capacity will be less..

That's why i asked above what the Vs were on the low end with the discharge current applied.

At least two of the problem batteries had a cell that settled under 3.4v while pack was being held at 56.2v.

I'm charging to 56.2v now, will hold until current drops off, then will do another 0.5c discharge test, but will let it run until Cell or Pack UVP, whichever comes first.

 

[underdog5004]

Well, I ran into cell OVP at 56v, so I'm backing off to 55.6v and holding there until current drops off

 

[SignatureSolarJess]

Reviewing the thread found a couple things:

1. Apparently, anything over 40mv (not 400mv) is considered imbalanced. @SignatureSolarJess why werent my batteries showing higher than 40mv diff covered under warranty?

2. @EG4TechSolutionsTeam you suggested discharging at 0.5c until undervoltage protection was engaged. According to BMS-test, UVP engages at 40v pack voltage, or 2.5vpc. Is it safe to bring my cells this low?

Hi again! I hope you're well! As we don't provide the warranty, any specifics would need to be addressed with the manufacturer. Seems you've got them tagged though, hopefully they can respond soon!

 

[underdog5004]

Hi again! I hope you're well! As we don't provide the warranty, any specifics would need to be addressed with the manufacturer. Seems you've got them tagged though, hopefully they can respond soon!

 

[underdog5004]

Ok, took the battery down to protection state. Cell uvp triggered first.

Looks like I got 99.6ah out of this battery, shockingly close to what the bms predicted.

5 more to go.

 

[BarracudaBob]

History Repeats itself. There is a good chance if you top balance it and cycle it a couple of times you will be in good shape.
Top Balancing welded cell batteries

 

[Q-Dog]

Is this one of the "good" batteries or one of the "bad" batteries?

 

[underdog5004]

Is this one of the "good" batteries or one of the "bad" batteries?

This is battery 1, one of the problem batteries, which showed a diff of around 140mv when floated at 56.2v

 

[underdog5004]

History Repeats itself. There is a good chance if you top balance it and cycle it a couple of times you will be in good shape.
Top Balancing welded cell batteries

I may have to!

 

[BarracudaBob]

This is battery 1, one of the problem batteries, which showed a diff of around 140mv when floated at 56.2v

If you can get them balanced either manually or my external active balancer way and get them up to 56.6V couple hours a week they will usually stay balanced. Getting out of unbalanced hell does take some effort. You just can't wish it away.

 

[fnnwizard]

Ok, took the battery down to protection state. Cell uvp triggered first.

Looks like I got 99.6ah out of this battery, shockingly close to what the bms predicted.

5 more to go.

Yep Cell UVP and OVP should always trigger first if bms is set correctly.

You'd want to note which cell(s) got down to uvp first. Those same cells, if consistent with the others, should show a slightly lower V when charged.

If the 2.5xx cells upon charging reach > 3.55 1st, they are suspect.
The 2.8xxV cells have ~4Ahr left in them since at a .5C rate you have about 5-6 minutes left = 4 ish Ahr.

You can record your screen (use OBS) with the bms tools so you can review how the cells act throughout. Even better is using home assistant if you know how to implement.

This is battery 1, one of the problem batteries, which showed a diff of around 140mv when floated at 56.2v

Yep, this helps to confirm the above ~4Ahr.

 

[underdog5004]

Yep Cell UVP and OVP should always trigger first if bms is set correctly.

You'd want to note which cell(s) got down to uvp first. Those same cells, if consistent with the others, should show a slightly lower V when charged.

If the 2.5xx cells upon charging reach > 3.55 1st, they are suspect.
The 2.8xxV cells have ~4Ahr left in them since at a .5C rate you have about 5-6 minutes left = 4 ish Ahr.

You can record your screen (use OBS) with the bms tools so you can review how the cells act throughout. Even better is using home assistant if you know how to implement.


Yep, this helps to confirm the above ~4Ahr.

Charging now, bring whole bank up to full charge. Bad weather coming, probably won't be able to capacity test for at least a week.

 

[fnnwizard]

Heres some empirical data for anyone who's interested.

These 2 packs were built right out of their boxes with no top balancing. Built in Oct, put them to use in Nov.

I don't know the number of hours each had to go through balancing to reach were they are today... thats too much data to go through.


I've attached the day's activities for Feb 17 from the morning at start of charging.
Far right column is cell V delta.

The most important data point in there is how the batteries act when charging at typical rates through 3.400 up to 3.600V.

There's barely any time for the BMS to balance the cells from 3.450V to 3.600V. That's less than 10min at .150A (150mA BMS is Seplos e10) before the inverter has to cut to float/balance mode.

Well, the 2 test packs are finally well within balance tolerance as of 3-23!
Will do cap testing at 100 cycles to see about degradation.

Adjusted CV to 55.2 and float to 54.6 ( was at 57 and 56.8 resp.) and now will just let it run hands off til then.

 

[EG4TechSolutionsTeam]

2. @EG4TechSolutionsTeam you suggested discharging at 0.5c until undervoltage protection was engaged. According to BMS-test, UVP engages at 40v pack voltage, or 2.5vpc. Is it safe to bring my cells this low?

While it is safe, I would make sure to have an additional battery charger available during this action.