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I think your LifePo4 graph is wrong and mixed it up with Li Ion. No graph on the net is this high of voltage as you show the curve to 4.2 volts and low to 2.5. Most LifePo4 shows 14 % which is right at the lower knee at ruffly 3.18 volts. Your graph shows almost 3.38 at 14% and this is definitely wrong.
FilterGuy
FilterGuy
Funny.... the graph shown was taken from the net.

2.5V to 4.2V are the extreme limits of discharge and charge without immediate damage on LiFePo4. There is little reason to push the cells to these limits because they are well past the knees of the curve and the last .5V-.75v past each knee adds very little additional storage.

The bulk of the storage is obtained between 3.3V and 3.6V and most people will set their system up to be within that range. The most aggressive use will operate pretty close to these values, but a lot of people like to set things significantly less aggressive than this in order to prolong the life of the batteries. The key is to set the chargers and load to typically operate in your preferred range and set the BMS (2nd line of defense) at values that are outside the range of the Chargers and Loads but still within the 2.5V - 4.2V range. (if the system is working properly, it will never hit the BMS values). The trick is to set the BMS range as conservative as possible, but far enough outside the Charger/Load range to avoid unnecessary trips of the BMS.
Great overview! While I am a EE, I appreciate the research you did so you could cover the many non-obvious side effects of power system grounding.

I have a suggestion: There are many examples on the Internet of fusing (usually circuit breakers) both the positive and negative connections for a device. In particular, I see many examples of this on the wires between the solar panel(s) and the solar charge controller.

From your discussion of grounding, this would seem to be counter productive, as well as unnecessary.

Some clarification on this issue would be of value to many of us.
Thank you!
FilterGuy
FilterGuy
Yes, that is a good point. The NEC requires a disconnect that breaks both positive and negative on the PV circuits...... and I have never seen that explained. Maybe if I go looking again I can find something, but last time I looked I found a lot of places that stated the requirement but no place that explained why. (I suspect you are like me.....I hate it when I can't explain the 'why' behind a requirement)
We would call it a fraud considering that amy must be a professional lyer considering what she is promisierung compared to what she has delivered. EVE sells the LF280 cell with test reports from the factory floor for free and their spec sheet tells you exactly how to measure the battery right and what to get: 280 Ah with a 1C testing which would equal 280A current and a discharge time of 1 hour.

you had piad 4$ extra for the testing where they discharged that roughly 10 times slower and then the 280 Ah is no longer valid cause it must be a lot higher if you discharge with lower A or C rate. But you just got 280,5 Ah guess and most likely at 25°C ambient temperature which means less resistance and therefore a lot more Ah. But you just got 280,5 Ah which would equal maybe 272 Ah with a full 1c rating test.

these are quite old most likely used cells and for sure not grade a cells at least if you compare them to the EVE reference document where they do explain how to determine if you got a good or bad cell.

Sad to see you being so ripped of.
Thank you so very much for answering all my questions and concerns.

You have helped make a very happy battery.
Great work! In regards to the 8s2p 24v layout, would you just connect the solar +/- wires to the same busbars as the batteries and bms's are joined at?
FilterGuy
FilterGuy
Please re-post this question on the general discussion forum and tag me with an @FilterGuy.
I've been searching for this exact information since I signed up here!
I couldn't have asked for a more thorough explanation. You're time and efforts are SO appreciated... 👏🙏👏🙏
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