Cinergi's 28 kWh / 4 kW Solar / 10 kW inverter RV build
- Thread starter cinergi
- Start date
OK, discharged to 0% (2.000 volts each actually). Raw numbers are below. I'm pretty sure I heard the springs a few times. Maybe I'll capture a time-lapse of this some day. These springs really should have a 3/8" rod between them (not 1/4" like I do). The springs are deforming a bit as a result.
Summary: The top springs expanded by about 1.7mm and the bottom springs by about 2.7mm. The terminals, after I removed the bus bars, were closer together (anywhere from 0.11mm to 0.96mm). My measurements were a little faulty there but it's obvious they got closer.
I think it's pretty clear that the solid bus bars are put under strain in this situation and prevent the compression fixture from evenly compressing (the top didn't compress as much as the bottom).
I will measure again after I recharge the battery.
At 100% SoC
============
Terminals
77.98
78.65
78.20
78.75
77.87
78.14
Springs
26.72 ("top left")
27.11 ("bottom left")
27.12 ("top right")
27.48 ("bottom right")
At 0% SoC
============
Terminals
77.65 (-0.33)
77.69 (-0.96)
77.80 (-0.60)
77.97 (-0.78)
77.51 (-0.36)
78.03 (-0.11)
Springs
28.46 (+1.74)
29.75 (+2.64)
28.78 (+1.66)
30.24 (+2.76)
Summary: The top springs expanded by about 1.7mm and the bottom springs by about 2.7mm. The terminals, after I removed the bus bars, were closer together (anywhere from 0.11mm to 0.96mm). My measurements were a little faulty there but it's obvious they got closer.
I think it's pretty clear that the solid bus bars are put under strain in this situation and prevent the compression fixture from evenly compressing (the top didn't compress as much as the bottom).
I will measure again after I recharge the battery.
At 100% SoC
============
Terminals
77.98
78.65
78.20
78.75
77.87
78.14
Springs
26.72 ("top left")
27.11 ("bottom left")
27.12 ("top right")
27.48 ("bottom right")
At 0% SoC
============
Terminals
77.65 (-0.33)
77.69 (-0.96)
77.80 (-0.60)
77.97 (-0.78)
77.51 (-0.36)
78.03 (-0.11)
Springs
28.46 (+1.74)
29.75 (+2.64)
28.78 (+1.66)
30.24 (+2.76)
For your 1/4 rod with the spring just put a sleeve on the rod so the tread will not affect the mouvement when the spring is expending
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Oh, hmm - good thought, I'll see if it fits over the tubing I'm using. It doesn't catch on the threads, fortunately. It's just warping because there's too much space on the inside.
Solarfun4jim
Solar seduced :-)
What was your reasoning for discharging to 2.0v/cell? I know you must have had a good reason, but i always thought 2.5v/cell was the cut off point for these type cells?
I may have missed some of your discussion on this previously....but i'd be interested to know.
It's one of the birds I'm killing with one stone. The reseller asked me to do that on my "bad" cells and then to charge and repeat my capacity test.
Solarfun4jim
Solar seduced :-)
wow...i always thought damage was done below 2.5v. Did they attempt to explain the technicalities behind this....that would be good info to know.
Michael B Caro
Solar Wizard
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We have been working with the supplier on this for some time now. This discharge to 2v was their most recent suggestion. All they said is:
"I ask the engineer, you can tell the customer, try to discharge to 2.0v, and see the capacity again"
This will be interesting. It's my understanding discharging a cell too much will reduce the capacity. I have no understanding how capacity would be increased. I don't know the threshold when damage starts below 2.5 volts, but there is a lot of difference between 2 and 2.5 volts. Also I don't know what effect this would have on cycle life. Is the supplier going to take liability if any damage is done to the cells?
These questions should have been addressed directly with EVE. I don't trust the suppliers "engineer" since no more information was provided. I hope I am wrong.
These questions should have been addressed directly with EVE. I don't trust the suppliers "engineer" since no more information was provided. I hope I am wrong.
Michael B Caro
Solar Wizard
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It is my understanding that these cells can be drawn down to zero, but repeatedly doing so will limit the number of cycles.
He is only doing it with his weakest 4 cells, so it is not the huge risk it would be otherwise.
If the engineer gave us all of the technical details, we still wouldn't now if we could trust what they say, so we would still be taking the same risk.
If damage is done to the cells by doing this one time, yes I will hold the supplier accountable and cinergi knows that I will take care of him even if the supplier does not. Refusing to take the steps the supplier asks us to would drastically limit the leverage we would have to demand suitable compensation from the supplier if the cells remain at too low of a capacity.
ArthurEld
Solar Wizard
It probably won't kill the cell to discharge it to 2V but there aren't any Ah between 2.5V and 2V.
So, I am doubting that is going to make a difference.
So, I am doubting that is going to make a difference.
Michael B Caro
Solar Wizard
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I have my doubts as well. But, cinergi does not mind jumping through this hoop and so we will.
I did tell him that if he was tired of dealing with all of their suggestions I would tell them no and force the issue of compensation now, but he said it was no problem to give it a try.
ArthurEld
Solar Wizard
I would try it too. It would be cool if you found 20Ah in there. I've never tried it.
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.
Solarfun4jim
Solar seduced :-)
That's a fair response....removing the ultimate risk from cinergi. This is great info to have on the resulting outcome.
Well done Michael. That buys you a lot of trust in my books.
Michael B Caro
Solar Wizard
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I assume as much risk as I possibly can for anyone that orders through me. I try to do for them what I would expect someone to do for me if I were on the other side of the table. I will not claim that there may not come a time when what the buyer thinks should be done differs from what I would expect if I were him, but I guarantee, at least from the situations I have run into so far, that I go above and beyond what the suppliers I have been working with do.That's a fair response....removing the ultimate risk from cinergi. This is great info to have on the resulting outcome.
Some thoughts:
- 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.
- At the same time, reseller's "engineer" (<--more on that below) is asking a customer to take their cells below the manufacturer's limits, to a voltage that might possibly even void the warranty if it were a new warrantied cell, without indicating why.
- What would be the upside of finding 20Ah hiding down there? It would still not be usable capacity, the 280Ah minimum is defined as being between 2.5 and 3.65/0.05C
- I agree with @Michael B Caro that the "engineer" providing more technical details would not make us automatically trust them, but I agree with @Gazoo that providing at least some amount of technical information and explanation would go along way to establishing at least a little bit of trust. Maybe what they are advocating is a well established troubleshooting step, or maybe its akin to "IDK maybe if he discharges lower there will be more capacity, worth a try"
- On the term "engineer," I have heard (but don't know for sure), the way the resellers reference 'the engineer' is very different than what we might think it means and certainly different than a university would define the term. That said, I think there is much variation between resellers and I won't rule out that there may be a few with an actual engineer on staff (maybe), and I suspect many where is a rhetorical tool not a person, and many where it means something along the lines of "our tech person / tech support person." I don't think its realistic or even necessary for every seller of discount cells to have an actual engineer on staff, I just think we need to be conscious that 'engineer' doesn't necessarily mean engineer. Of course you have more familiarity with the resellers you buy from so you may have more insight/info.
- The fact that this is all only for @cinergi's 4 weakest cells makes it low risk in his case.
- As to refusing to take steps a supplier asks for: refusing outright maybe, but asking for explanation of any troubleshooting step but especially one that violates manufacturer limits, is not unreasonable, and is well short of refusal.
- @cinergi deserves an award for 2nd best customer for all the time and effort, and good will, and flexibility! (first place (from the resellers point of view) of course goes to the many hundreds of people who bought (and still buy) cells without testing or verifying anything and just chose to believe/profess that they got Grade A cells without testing)
- Final thought, I wonder if there is some logic behind this troubleshooting step that we could learn from. Some muse that the occasional full cycle up to 3.65 is good for maintaining capacity over time. Others say this is BS. Some have said they found a little extra capacity after a few cycles. But I've never heard anyone advocate an especially deep discharge to increase capacity (in the normal bandwidth limits) and I have no idea if this is the resellers logic or not. It would be interesting to know the why and the how behind this troubleshooting step. If there was any logic to it, it could help others. But as @Gazoo mentioned, it would be more reassuring to hear it from EVE or an academic source. Still following up for an explanation could benefit others.
I've noticed a correlation between me starting a comment with "some thoughts" or "a few things to consider" and writing way too much. Hiding the ramble behind a spoiler tag..
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In no way did I mean to imply you don't take care of anyone buying cells from you. I know you do, always have and always will. I trust you, and have trusted you 100%. I am sorry if you took anything I said differently, even a little bit. It's the suppliers I don't place 100% trust in and by suppliers I mean all of them, although some are better than others. But you are the best...
Michael B Caro
Solar Wizard
- Joined
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Nope. Didn't take offense at all....not sure what I said that made you think I might have. If I had took offense, you would have known about it, in no uncertain terms LOL. But in a "conversation", not out in public.In no way did I mean to imply you don't take care of anyone buying cells from you. I know you do, always have and always will. I trust you, and have trusted you 100%. I am sorry if you took anything I said differently, even a little bit. It's the suppliers I don't place 100% trust in and by suppliers I mean all of them, although some are better than others. But you are the best...
