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diy solar

Cinergi's 28 kWh / 4 kW Solar / 10 kW inverter RV build

It was under 1Ah between 2.5 and 2.0 volts. Which is why I don't believe it's particularly damaging because we didn't really extract that many more electrons / move that much more LiFe around... and I immediately started charging the cells.
I am anxiously waiting for your results. Are you done charging yet...lol. Seriously thanks for all your updates.
 
The one comment I will pull out of my self imposed spoiler quarantine, is that: if there is actually some logic/science behind the discharge down to 2.0V beyond ('its worth a try') it may benefit us and others to understand that logic. Some people (that I mostly trust, but aren't infallable) have observed positive benefits to completing full cycles to ~3.65 every so often. But I've never heard of anyone even muse about the opposite (full--or in this case 'over'--discharge) having any benefit whatsoever. Maybe they just want to test a lower voltage to rule out any slight measurement errors.
 
The one comment I will pull out of my self imposed spoiler quarantine, is that: if there is actually some logic/science behind the discharge down to 2.0V beyond ('its worth a try') it may benefit us and others to understand that logic. Some people (that I mostly trust, but aren't infallable) have observed positive benefits to completing full cycles to 3.65 every so often. But I've never heard of anyone even muse about the opposite (full--or in this case 'over'--discharge) having any benefit. Maybe they just want to test a lower voltage to rule out any slight measurement errors.
Maybe. I am not much of a technical guy. It took me a while to even look into "desulfating" with FLA batteries. lol
 
Below 2.5V there is less than 0.2% lithium ions left to move IIRC. I have not seen any research supporting going that low for any reason.
 
Perhaps @Dzl is referring to the formation process that is typically done at the factory?
This is pure speculation, but if these cells are culled after first formation charge at the factory, perhaps there is some benefit of doing that one or two times more? @Steve_S has talked about the benefits of "trash testing" these cells. Other than that wild ass speculation. I would not be doing that to my cells. I am comfortable only using 80% of these cells capacity and only going from 3.0 to 3.4 volts.
 
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The one comment I will pull out of my self imposed spoiler quarantine, is that: if there is actually some logic/science behind the discharge down to 2.0V beyond ('its worth a try') it may benefit us and others to understand that logic. Some people (that I mostly trust, but aren't infallable) have observed positive benefits to completing full cycles to ~3.65 every so often. But I've never heard of anyone even muse about the opposite (full--or in this case 'over'--discharge) having any benefit whatsoever. Maybe they just want to test a lower voltage to rule out any slight measurement errors.

That's one of the reasons I chose to do this - I want to see if there's any truth to this.
 
Perhaps @Dzl is referring to the formation process that is typically done at the factory?
Which of my comments are you referring to? This one?:
Risk of significant damage from a single cycle down to 2.0V is higher than 2.5V, but maybe not excessively risky for someone as attentive (and at this point intimately familiar with his cells) as @cinergi. 2.5V is the minimum voltage as defined by the manufacturer (nearly all manufacturers), but in a academic/research context cells are routinely taken down to 2.0V.
If this is what you were referring to, I only mean that in many of the research papers I have encountered for the purposes of testing/research only, they often take cells down to 2.0V or thereabouts. This is not to say they or anyone else reccomends it, or that it won't harm the cells, or shorten cycle life (it might, that isn't really a concern for researchers just looking to test some hypothesis or another, cells are expendable in that context). So to be crystal clear. Saying researchers do it is in no way saying its advisable or that researchers condone it. I would not go below 2.5ish volts personally, at least not without being convinced of a very good reason. And I want to make sure my comment isn't misunderstood as condoning intentionally exceeding manufacturer defined limits.

I may have misunderstood what you were referencing but I wanted to nip it in the bud if it relates to the 2.0V thing.
 
Which of my comments are you referring to? This one?:
I was referring to the comment that @cinergi quoted above that reminded me of what @Steve_S was doing. I made my own connection of that to the formation process done at the factory. My response was off the cuff and actually a sidetrack from meat of the 2 volts discussion. I have not done the kind of trash testing that Steve has done and am happy only using 80% of the capacity of my cells.
 
Pinged 2x:
My thrash testing was only between 2.500-3.650 and not beyond specifications for Charger/Discharge rates.
I did not read this thread here for quite a while. (not following threads) so I'm now aware of the content of the ongoing discussion.
I can say, that Capacity retention improved "slightly" after 2 deep, top to bottom cycles, the AT REST voltage (post charge settling) only went up on average of 150mv.
Between 3.00-2.500 and 3.450-3.650 is really minimal AH. On 280's my observed guesstimate it's likely not more than 10-13AH at best.

I dunno if that helps at all.
Steve
 
My 2 cents worth....
As a beginner, you start to appraise your cells/battery pack using very low C rates, eg Bench power supply to charge up, 150w capacity tester to discharge down. This provides basic info about your pack. As a 'first time' beginner, much of the theory seems confusing, but only once you have actually completed the process of testing, then a lot of the info just falls right into place. From intial testing, you get an idea where your cells start to diverge and the delta differences between the cells, the point at which one cell will really run etc etc. This picture however, changes somewhat, when you 'thrash test' or even just apply realistic operating values, at which point, you only then get to 'know' your cells.
 
I did the Thrashing for my own curiosity to see what the cells & assembled packs would do and how they would behave when pushed. I do not like unexpected surprises (especially when I have to depend on whatever the item is), so I would rather have "control" and push things to the edge without causing myself or my gear harms. My system is built to handle 300A and I had to know that it would do it without a blink.
 
Battery is recharged. Measurements:

Springs
TL 28.41 (-0.05)
BL 28.01 (-1.74)
TR 28.35 (-0.43)
BR 28.46 (-1.78)

All terminals remained at 78mm.

You can see that the top barely re-compressed, likely due to the rigid bus bars. I even disconnected the bus bars to see if it would squeeze in more -- and they did not. The top measurements remained the same.
 
You can see that the top barely re-compressed, likely due to the rigid bus bars. I even disconnected the bus bars to see if it would squeeze in more -- and they did not. The top measurements remained the same.

After you took a bite and the peanut butter and jelly squeezed to the other edge of the bread, nothing to make it flow back.
Anybody got Ansys, want to make an animated model of LPF material getting squished around?
 
After you took a bite and the peanut butter and jelly squeezed to the other edge of the bread, nothing to make it flow back.

It's comments like these that make me appreciate the diversity among us. I would never have drawn that analogy on my own.
 
Battery is recharged. Measurements:

Springs
TL 28.41 (-0.05)
BL 28.01 (-1.74)
TR 28.35 (-0.43)
BR 28.46 (-1.78)

All terminals remained at 78mm.

You can see that the top barely re-compressed, likely due to the rigid bus bars. I even disconnected the bus bars to see if it would squeeze in more -- and they did not. The top measurements remained the same.
Very interesting data, but it’s a long thread so it would help to repeat the basics:

How many cells in your string?
What is the spring force (psi) you estimate you are applying at 0% and 100% SOC?

I saw the earlier post were you were concerned about the movement you saw, especially in regards to what that translates to in terms of stress with solid busbars - so what does that mean in terms of ‘terminals remained at 78mm’?

-original position at 100% was > 78mm?
-upon discharge to 0%, terminals moved to 78mm?
-and upon recharge to 100% terminals remained where they were (78mm)?

Are you loosening and retightrning busbars at 0% and 100% or have they been left alone since first attached?
 
Can I suggest you guys break out the bottom balance conversation if you want to continue discussing? There is incorrect information in here about it which would be nice to resolve, but not here. Thanks! :)
 
I was referring to the comment that @cinergi quoted above that reminded me of what @Steve_S was doing. I made my own connection of that to the formation process done at the factory. My response was off the cuff and actually a sidetrack from meat of the 2 volts discussion. I have not done the kind of trash testing that Steve has done and am happy only using 80% of the capacity of my cells.
I think this is relevant https://diysolarforum.com/threads/l...tep-in-fabrication-of-li-ion-batteries.11983/
 
Can I suggest you guys break out the bottom balance conversation if you want to continue discussing? There is incorrect information in here about it which would be nice to resolve, but not here. Thanks! :)
Back OT, I circled back and believe I’ve understood that your pack is 8S, correct?

The ‘spring’ data is clear but I’m still confused by the 6 terminal measurements you had - was that center-to-center measurements for the 6 central cells?
 
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