First review of using 280 ah cells in real life conditions

[Jejochen]

So after a month of using my powerwall with 86 kWh 280 ah xuba cells, the darker days are coming.
Until now with enough sun to always have the battery charged to the upper regio's, the cells performed good. Big powerdraw from the cells if neccesary is not a problem.
However, as the sun is more and more fading, the cells are starting to occasionaly get in the lower regions of voltage. And at the lower voltages, they start drift quite a lot. The bms cuts the power when the cell with lowest voltage hits 2.8, and the shunt data indicates there is still 37 % power left in de battery.
Price of the cells is good, but this a little (?) downside. I will now power the pack to full 100 % and let everything balance before using again, and will come back on the future numbers.

 

[curiouscarbon]

Passive balancing at top of charge only?

Curious if rebalancing will fix, in worst case active balancing for lower SoC..?

Cheers and hope the voltages are matched across all SoC soon.

 

[Jejochen]

Passive balancing at top of charge only?

Curious if rebalancing will fix, in worst case active balancing for lower SoC..?

Cheers and hope the voltages are matched across all SoC soon.

Yes, passive top balancing.
I hope i can get it fixed, kinda sucks

 

[curiouscarbon]

I am sure you can figure it out.

If it’s the same cells wandering in the same way, maybe try to take them out of service and test individually and replace if results warrant it.

Could be cable imbalance, if the spatial pattern of drifting is plausible (more busbar?). e.g. close ones dip first far ones dip last

Your build is inspiring; I’m certain you have the mental capabilities to diagnose and fix this.

 

[solarsimon]

is it 6P16S ?

 

[Jejochen]

is it 6P16S

6 packs, 16s

 

[nebster]

Well, if it helps, I have a 3p16s and am able to achieve 98% of stated capacity with a single bottom-balance and after about 20 cycles. I doubt your pack is properly balanced, or I suppose you might have a wiring issue dumping energy somewhere you don't intend to. Or you could have a bad cell, of course.

 

[Jejochen]

Ok, an update:
So i topbalanced all the cells again. I let the batrium, and helped the blockmons on a few cells to speed up the proces. At the top voltage, lowest cell voltage was 5.53V, highest 5.55V.
I let the inverters run, and after a few days (no charging, solar is removed as the roof is being renewed) i got this good result:

10 % isn't the bottom yet, this is the treshold the inverters stop when there is still gridpower. When the grid fails, it will use the remaining energy for emergencies)
So that's a lot better, but it is only the first run. When all the solar panels are back, real life testing can again start.

 

[Capt Bill]

d at the lower voltages, they start drift quite a lot.

Wondering. Did you start out with a Parallel 3.2v LiFePO4 cells configuration and Top Balance by charging all that to 3.6 or 3.65 volts ? I am asking from a personal lesson perspective. I recently mixed a new replacement cell in my 24v LiFePO4 bank at close to matched cell voltage, and thought depending on my battery charging cycles and bms balancing, that would be good enough. That proved to be a failed approach as the new replacement cell drained early. After I correctly top balanced, all the cells drained uniformly. My Two Cents.

 

[Jejochen]

Wondering. Did you start out with a Parallel 3.2v LiFePO4 cells configuration and Top Balance by charging all that to 3.6 or 3.65 volts ? I am asking from a personal lesson perspective. I recently mixed a new replacement cell in my 24v LiFePO4 bank at close to matched cell voltage, and thought depending on my battery charging cycles and bms balancing, that would be good enough. That proved to be a failed approach as the new replacement cell drained early. After I correctly top balanced, all the cells drained uniformly. My Two Cents.

yes, all 96 cells had been paralleled and top balanced. before installation.

 

[Luthj]

Does your BMS have internal resistance calculation function? I was experiencing some drift, and found I had a couple of higher resistance bus bar connections. Some 1000 grit polishing on a flat surface did the trick with those. You might also see what your start balancing voltage is, if its fairly high, you might not be getting enough balance time at the top of each charge.

 

[HRTKD]

@Jejochen , how is your battery bank doing?

 

[Jejochen]

Quite good. I did a new topbalance, and everything seems to stay more at the same level. The system is beeing quite intense used, with discharge (aprox 35 to 40 % discharge a day) and charge daily. At this time i couln't be happier. The harder testing of cell levels will be at the darker times however when the battery stays more in the lower regions of SOC

 

[linkcat]

Quite good. I did a new topbalance, and everything seems to stay more at the same level. The system is beeing quite intense used, with discharge (aprox 35 to 40 % discharge a day) and charge daily. At this time i couln't be happier. The harder testing of cell levels will be at the darker times however when the battery stays more in the lower regions of SOC

Any updates on this? How much % are you able to discharge?

Cheers