Issues balancing with Batrium BMS

[OffGridInTheCity]

What I don't understand is why do the lower voltage cells have higher bypass mAh? Wouldn't the higher value cells be the ones burning off mAh? Or do I have it backwards?

I agree, Batrium 'burns off' the higher cells to lower them. As to why the info is not making sense - as I wrote above, I've never unerstood the Batrium Telemetry report mah metrics and just took to monitoring the Blue Bars + I extract the cell voltages and put them in a DB so I can report on Highest / Lowest and max difference for monitoring

For example, it's been about 5 months since I balanced and I'm running 40mv to 80mv differences thru the charge cycle. These are a variety of Lithium-ion cells so it's not as tight as you're LifePo4 but I don't need it tight - just to be consistent.

Here's an example of my dashboard monitor line... currently at 50mv max difference:

Lowest 7: 3.64@P88, 3.64@P100, 3.64@P101, 3.64@P102, 3.64@P108, 3.64@P109, 3.65@P16 (0.05v) Highest 7: 3.69@P12, 3.69@P14, 3.69@P27, 3.69@P55, 3.68@P7, 3.68@P6, 3.68@P5

Lowest is Pack 88, 100, 101, 102, 108, and 109 at 3.64v. Highest are Pack 12, 14, 27, and 55 at 3.69v.

 

[hummmingbear]

Your intuition is correct. Given that the mAh values are resetting themselves, it's hard to compare them.

You should see more intuition-consistent behavior if you reduce the bypass banding to 0.01, it should force the unit to just work on the highest 0.01V cells.

Ok, changed it to 0.01

FWIW I am definitely seeing an improvement! There is only one cell at 3.38 and the other cells that had previously been low are in the 3.42-3.44 range which is very acceptable. I think patience is what I needed but also my bypass settings needing some tuning as well, so I think this has been really helpful. I'll keep posting updates here

 

[hummmingbear]

I agree, Batrium 'burns off' the higher cells to lower them. As to why the info is not making sense - as I wrote above, I've never unerstood the Batrium Telemetry report mah metrics and just took to monitoring the Blue Bars + I extract the cell voltages and put them in a DB so I can report on Highest / Lowest and max difference for monitoring

For example, it's been about 5 months since I balanced and I'm running 40mv to 80mv differences thru the charge cycle. These are a variety of Lithium-ion cells so it's not as tight as you're LifePo4 but I don't need it tight - just to be consistent.

Here's an example of my dashboard monitor line... currently at 50mv max difference:

Lowest 7: 3.64@P88, 3.64@P100, 3.64@P101, 3.64@P102, 3.64@P108, 3.64@P109, 3.65@P16 (0.05v) Highest 7: 3.69@P12, 3.69@P14, 3.69@P27, 3.69@P55, 3.68@P7, 3.68@P6, 3.68@P5

Lowest is Pack 88, 100, 101, 102, 108, and 109 at 3.64v. Highest are Pack 12, 14, 27, and 55 at 3.69v.

Their settings have always been quite confusing to me...can't tell if I haven't given it enough time or if it's just poorly worded. In anycase I feel similar that I track the graph and that makes the most sense to me. I think I'm out of the hole here. A day or two more and I think i'll be back in balance

 

[sunshine_eggo]

Their settings have always been quite confusing to me...can't tell if I haven't given it enough time or if it's just poorly worded. In anycase I feel similar that I track the graph and that makes the most sense to me. I think I'm out of the hole here. A day or two more and I think i'll be back in balance

The thing is all cells have to be pulled down to #48.

 

[hummmingbear]

The thing is all cells have to be pulled down to #48.

well, they have to be pulled down until they are within range of eachother for balancing to stop? Is that what you mean?

 

[hummmingbear]

That's what I'd like to understand better.

Later in absorption means lower amperage. Either the cells aren't seeing full amperage or the those cells need higher amperage to maintain the voltage.

Could be a red herring inherent to having cells that are not perfectly matched.

I even see this now with my last cell, it drops lower through absorption and balancing. The other cells were doing that too but have gotten better after 2 days of balancing

 

[sunshine_eggo]

well, they have to be pulled down until they are within range of eachother for balancing to stop? Is that what you mean?

Yes. Once all cells are within 0.02V, balancing will stop. At that point, you can disable auto level and use the bypass voltage for balancing.

If you have the ability to charge that one cell independently, it might be worthwhile to charge it @ 3.45V when the other cells are at 3.45V and balancing.

If you have the typical 30V/10A PSU, you can connect to that cell without breaking the battery down.

 

[hummmingbear]

Yes. Once all cells are within 0.02V, balancing will stop. At that point, you can disable auto level and use the bypass voltage for balancing.

If you have the ability to charge that one cell independently, it might be worthwhile to charge it @ 3.45V when the other cells are at 3.45V and balancing.

If you have the typical 30V/10A PSU, you can connect to that cell without breaking the battery down.

That cell actually is accessible 1-32 are not easily. Good point. I have a DC charger that i can set to 3.450...I might just do that tomorrow once all the other cells reach that. Thanks for all the help, this has been fun

 

[sunshine_eggo]

That cell actually is accessible 1-32 are not easily. Good point. I have a DC charger that i can set to 3.450...I might just do that tomorrow once all the other cells reach that. Thanks for all the help, this has been fun

I've seen situations where a battery that was top balanced was left to sit for several weeks, and a very small imbalance developed. Simply put the 30V/10A supply on each cell @ 3.65V. The 2X 8 batteries took 2-10 minutes per cell to charge without breaking them down. Once finished, top balance was restored.

 

[hummmingbear]

We are back to rain for the next 3-days...so I'll have to continue the saga when we get some sunshine again. Really appreciate everyone here! And @sunshine_eggo if i can buy you a coffee or beer somehow let me know!

 

[hummmingbear]

Just a quick update here, all but two cells are at 3.45v! One of them is close enough for me (3.43). The other cell is still a bit low (#48 from the batrium display) @ 3.37. I've been meaning to open my case up to manually charge this one once I'm in absorption but haven't gotten to it...I'll make some time tomorrow.

Below is another chart I pull data into and can see back in time, these are the cell values just before it dropped into float

 

[OffGridInTheCity]

Cool. Did you reach any conclusions on why these cells dropped in voltage in the first place?

 

[hummmingbear]

Cool. Did you reach any conclusions on why these cells dropped in voltage in the first place?

This is my hunch. We had about 3-4 weeks of clouds/rain. The battery mainly stayed between 30-80% for that entire time, mostly on the lower end. A couple times it got as low as 12-18% but no cell went below than 3.1v. My guess is that some drift happened in there, probably due to mismatched resistance of the cells. Maybe I need to double check my busbars/nuts as well but I tightened everything to spec.

Winter is cloudy here but come spring-fall we almost always get sunny days.

 

[sunshine_eggo]

This is my hunch. We had about 3-4 weeks of clouds/rain. The battery mainly stayed between 30-80% for that entire time, mostly on the lower end. A couple times it got as low as 12-18% but no cell went below than 3.1v. My guess is that some drift happened in there, probably due to mismatched resistance of the cells. Maybe I need to double check my busbars/nuts as well but I tightened everything to spec.

Winter is cloudy here but come spring-fall we almost always get sunny days.

I thought one or two of these were new batteries, and they were never top balanced? Did I make that up?

 

[hummmingbear]

I thought one or two of these were new batteries, and they were never top balanced? Did I make that up?

All of them are new, I just put them into service in September. I top-balanced them right before they went into service. They never went this far out of balance until after this long stretch of not being fully charged. Is that normal or no?

Update from today, they are back in balance. I charged up cell 48 with my DC charger and brought it up to 3.45 in under 10min

 

[sunshine_eggo]

As you just discovered, even very slight imbalance (10 minutes @ 10A?... 1.7Ah?) can make a noteworthy difference.

Normal to go out of balance? No.

Uncommon? No.

Gray market cells are not matched (regardless of what your vendor claims). If all of your cells have slightly different self-discharge rates, then they will go out of balance if not kept in the balancing range long enough.

 

[OffGridInTheCity]

@hummingbear - I wanted to explain why I appreciate you sharing this 'incident'. I have over 100packs, some are nearing 5 years old / 1,600 cycles. While mine are lithium-ion and yours are LifePo4 - the concept of powerwall cell/pack maintenance isn't often shared/discussed but of course it can happen. Batrium helps provide an exceptionally clear visual into this.

In my case, I don't know when I'll see issues but the years are going by and it's bound to come. I imagine I'll see weak packs, do some balancing, and it will gradually get worse and eventually I'll have to retire a pack (or several packs). But I'm not sure what pack failure will look like exactly and how fast it will progress.

As your continue operations, I'd be very interested to read about any further 'incidents' and what you eventually conclude.

 

[hummmingbear]

@hummingbear - I wanted to explain why I appreciate you sharing this 'incident'. I have over 100packs, some are nearing 5 years old / 1,600 cycles. While mine are lithium-ion and yours are LifePo4 - the concept of powerwall cell/pack maintenance isn't often shared/discussed but of course it can happen. Batrium helps provide an exceptionally clear visual into this.

In my case, I don't know when I'll see issues but the years are going by and it's bound to come. I imagine I'll see weak packs, do some balancing, and it will gradually get worse and eventually I'll have to retire a pack (or several packs). But I'm not sure what pack failure will look like exactly and how fast it will progress.

As your continue operations, I'd be very interested to read about any further 'incidents' and what you eventually conclude.

Time will tell! I'll keep updating here occasionally and let ya know how it goes. Thanks for chiming in!

 

[jtvt]

How is cell 48 behaving?

 

[hummmingbear]

How is cell 48 behaving?

Generally fine, lowest cell has been 3.43 but all others are at 3.45. That's acceptable for me but still need to investigate why that one cell is consistently low. Might be my bus bars need to be inspected or that cell may just have a higher resistance. TBD

We have had a TON of snow the past week so not getting a full charge really.