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Why do 2 batteries in series 'tend' to be stable?
#21
You might get a better read of the SoC of each pack by charging to say 95% & 4.10V/pack
If Batrium shows the voltages of some packs floating higher sooner, etc there might be more balancing needed?

My (LiFePo4) packs tend to track in voltage nicely together too but minor imbalances only show towards either end of the SoC range.
Running off solar, DIY & electronics fan :-)
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#22
(07-30-2020, 04:17 AM)Redpacket Wrote: You might get a better read of the SoC of each pack by charging to say 95% & 4.10V/pack
If Batrium shows the voltages of some packs floating higher sooner, etc there might be more balancing needed?

My (LiFePo4) packs tend to track in voltage nicely together too but minor imbalances only show towards either end of the SoC range.
@Gauss163 has made a good point that LifePo4 is a significantly flatter discharge curve than 18650 - e.g. 0.05v max difference in 18650 Lithium-ion packs is not as critical as LifePo4.    

For test purposes, I have taken the current set of packs up to 4.10v successfully and maintained a <0.06v max difference - so I'm good as that was only a test.   Trying to balance the 84 packs to <0.04v max difference just isn't worth the time/effort - it doesn't matter as they hold steady and I won't be going anywhere near 4.10v for a long time...
 
So far, I'm averaging a top charge of 3.92v/pack daily as driven by my PV input and consumption profiles - which is per design to help extend the life of the battery bank.   I will have to gradually increase the voltage range as the battery bank degrades to store the same amount of PV power each day....  but hopefully that's a few years in the future and the balance profile is not yet known.   

On the one hand, I'm anxious to see what happens - but at the same time I  hope it take years for things to start 'south'...  Smile
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#23
Good points.
(07-30-2020, 03:35 PM)OffGridInTheCity Wrote: On the one hand, I'm anxious to see what happens - but at the same time I  hope it take years for things to start 'south'...  Smile
Same thing I thing of ! :-)
Running off solar, DIY & electronics fan :-)
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