House Battery and Energy Management

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Wolf

Active member
Joined
Sep 25, 2018
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1,608
@OffGridInTheCity will probably chime in but at that voltage there really isn't much usable power left. Maybe 200mAh per cell if lucky.
Also if your cutout is above the cell spec of generally 3.0V you extend the life of the cell considerably. Same goes with not charging the cell all the way to 4.2 but to ≈4.0V
Also in my study https://secondlifestorage.com/index.php?threads/behaviour-of-cells-in-parallel-take-2.8857/ I found out that below that voltage cells, especially in frankenstein packs/batteries will contribute differently to satisfy the load. Which can cause some cells to stress far more than others leading to premature failure.

Wolf
 

OffGridInTheCity

Active member
Joined
Dec 15, 2018
Messages
1,781
@OffGridInTheCity will probably chime in but at that voltage there really isn't much usable power left. Maybe 200mAh per cell if lucky.
Also if your cutout is above the cell spec of generally 3.0V you extend the life of the cell considerably. Same goes with not charging the cell all the way to 4.2 but to ≈4.0V
I have a 14s lithium-ion battery bank - e.g.48v nominal. I've found that my discharge curve knee is right at 49.5v - e.g. 3.54v/cell. @Wolf is correct that there just isn't much power below 3.5v/cell - its *dramatic* and why stress the cells for almost no power? Better to just build a bigger battery in terms of life span.
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In my particular case I could cut-off sooner and charge a bit higher... e.g. 3.57v - 4.04v for example - but I don't have *any* insight if moving the operating range up/down a bit will extend the cycle count beyond that Battery University graph.

Also in my study https://secondlifestorage.com/index.php?threads/behaviour-of-cells-in-parallel-take-2.8857/ I found out that below that voltage cells, especially in frankenstein packs/batteries will contribute differently to satisfy the load. Which can cause some cells to stress far more than others leading to premature failure.

Wolf
This is another reason, and it manifests in my battery as significantly diverging pack voltages below 3.5v/pack. I know it seems like you should be able to go to 3.4v/cell or 3.3v/cell or even 3.0v/cell but its like going over a cliff - no significant power below the knee.
 
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