There is something that it<s still strange to me:
He did a video about TS cells where he charged a TS cell at 1C and had let the voltage to rise up to 5.2V for the CV phase until he noticed that when the current began to drop.. then he droped the voltage to 3.7v and noticed that the current was very close to C/20, indicating the normal end of discharge.
He claimed that its not the voltage level that kill or dammage a cell.. but its the overcharge in capacity ( ex: let a cell reach C/20 at 5.2V)
Instead of C/20 at 3.7V in normal condition or 4.2 at low temp i believe...
If he only could open his mind and test what WE TESTED and understand, his presence in the EV community and the time he spend to share knowledge would be alot appreciable!
Doc
If you would open your mind, it would not be so strange to you. You take little scraps of information, and repeat it to each other long enough, it becomes fact - but only in your mind. You clearly do NOT understand what the maximum "voltage" is on the spec sheet in front of you. I was trying to explain it in the video.
The cell is fully charged at 3.4 vdc. It always was. There is no other "real" voltage. They do not like to be overcharged. The manufacturer gives you a "charge voltage" based on a standard charge current. This is a very brief description of a CC/CV curve. They can describe it essentially in one term - max voltage. IF you charge at ANY current until you reach a maximum voltage of 4.2 v, and then hold that voltage in CV phase until current decreases to 0.05C, you will have fully charged the cell. And if you let it rest a few minutes and measure the static voltage, it will indeed measure something like 3.38 or 3.40 volts. That is the ONLY voltage that actually ever mattered. The 4.2v is a short hand for A, as in 1, as in 1 of MANY, as in fact in 1 of an almost INFINITE, number of charge curves that would also get you to fully charged - 3.4 vdc static.
There never was any magic in it. If you look elsewhere on the spec sheet, you will also see that you can charge at current levels up to 3C. And in fact I have done so. And it works just fine. And nothing gets fried. And its all good. But of course the voltage at the terminals is WAY beyond 4.2 v. As it always would be at 3C.
The voltage at the terminals during charge never did matter. It was a target. The only voltage that matters is the voltage of the cell itself, which you do NOT want to go over 3.4 vdc static. The problem is how do you "get there." Here's a real slow way. Charge at whatever voltage and current you like for a couple of minutes. Now wait five minutes for the cell to return to a static level and measure it. Now repeat. It will take you about 3 days to charge the cell. But it will work.
The CC/CV to 4.2 is a charge curve methodology that will allow you to get there actually at a variety of current levels you would be likely to have available. If you pick 4.1 v and do the same thing, you will undercharge a smidge, but not much. And that will likely increase the life of your cells.
In practice, we charge serial strings of TS cells to 3.65 vdc. And the little bit of additional charge we fail to put in, is very minor. And it prolongs the life of the cells.
The point made, that you missed because your mind is closed and you already know everything from having typed so very very much, is that currents up to 3C can be accommodated, and the voltage you are so busily monitoring with your BMS and guarding against, isn't what you thought it was. It is a CC/CV description. Nothing more.
I find it beyond belief that you silly people have actually denigrated my reporting real test data BECAUSE I'VE DAMAGED CELLS????? What idiots, and from what planet? I don't lose ANY cells on my car. And I rather view it as my job here to damage cells otherwise. THAT'S HOW YOU LEARN. Your mission is to preserve your cells and I all too well understand why and sympathize with completely. They are expensive. They are ALSO expensive FOR ME. But there's not much to learn about a cell that works fine, and after using it, also works fine. THis is precisely how all this online typing/mythology gets so carried away. You learn NOTHING, and then make up some wild shit to explain it, and then repeat it to each other. THEN YOU ALL VOTE ON IT. Yep. That's what's right. More of us believe it than don't believe it AND SO IT BECOMES SO.
You're not going to learn anything about LiFePo4 cells without hurting them. That's pretty much what I do these days, torture and murder LiFePo4 cells. And the whole point is so that you don't have to. And I've kind of taken that as a little bit of a mission for you. Then you claim I don't know anything about them because I've killed them? A fine thanks that is.
On this specific point you can quite handily charge at current levels up to 3C, though it is noted that there is some loss of capacity in doing so. And your voltage can be quite beyond 4.2 vdc when you are doing so. The problem is then detecting when to terminate the charge so they are not overcharged. And the voltage you read at the terminals while charging has no bearing at all on it, which is why your BMS strategies are simply nonsense. By making them ever more convoluted and ever more complicated, you never seem to get there, because what you're doing doesn't need to be done in the first place.
NOW all the rage is LV cell detection. I can absolutely and definitively demonstrate cell voltage levels QUITE below 2.0 v on FULLY charged, fully functional perfectly operational cells that are in fact doing precisely what they should be doing. I'm not philisophically opposed to the concept of LV monitoring, I don't even understand what you are trying to do or why you are trying to do it. And that's because YOU don't understand how they work - after playing with them since 2007. They can quite commonly read below what you're monitoring for without having any cell problems at all, just a high current demand for a brief period. The same cell, showing an even HIGHER voltage under a lesser load, could be badly badly damaged and about to go far far away at any moment and your monitor won't even peep. Ergo my question, entered with a quite open mind, you are monitoring FOR WHAT, and you are going to do WHAT with the information??????
And I do know how it all happens. You take measurements under static conditions or at very low current levels, and extrapolate them endlessly by typing on your keyboard about it a lot. I want you ALL to go get these Cell Log 8S devices. That will allow you to record actual cell voltages under actual driving conditions in differing temperatures and then review it on a computer screen. I think you'll get a lot smarter that way then by typing a lot, and my job will be a lot easier. What you will see is that the "voltage" of the cell varies a lot more than you think, depending first on current loads, and then varying from THAT depending on what part of the discharge curve you are on, and then varying from THAT depending on ambient temperature, over such a wide range that the entire concept of LV cell monitoring becomes ridiculous.
How would actually monitor anything useful? Well that pretty much requires some "comparative" analysis. We can assume a couple of things here. The current through one cell will be pretty much identical to the current through all the other cells. The ambient temperature may vary slightly but should be broadly the same for all the cells. And so the voltage of any particular cell, should be pretty close to the voltage of any other cell, under the same conditions.
We use a totally idiotic circuit that measures the bottom half of the pack voltage and compares it to the top. It displays a centered bar on a bar graph. If either half varies from the other by more than a few tenths, the bar moves a digit right or left. At rest, it is more or less centered. Under acceleration, all cells are carrying identical current, and while there is some small variation in internal resistance and voltage, they are pretty close. And so it stays centered at rest, at 10 amps, at 100 amps, at 300 amps, and at 540 amps. It also stays centered at the top of charge, at 50% DOD, and at 80%DOD. And it stays centered at 100F, at 75F, at 45F, and at 10F. If it goes off center by more than a few bars, you should check your individual cells. And I'm particularly looking for variation under significant load, because that tends to indicate an increasing internal resistance, a sign of a failing cell that either needs attention or replacement BEFORE it fails completely.
The Cell Log 8S actually will do this kinda/sorta in a more needlessly complicated way, and still satisfy your insatiable desire to dick around with these batteries constantly. You can set the alarm to work on a difference voltage, such that if any cell varies from the other 7 by a set amount, it will trip the alarm. It is more complicated, more expensive, and no more effective, but it will give you something to do, and it IS kind of of value to then go look at the logs and see the bad cell sagging dramatically more than the others on the graph from actual drive data. So it is a learning experience that involves almost no typing or repeating of common wisdom endlessly.
Truly truly, it is NOT my mission to upset all these apple carts and dethrone the little tin forum Gods that have gained such a following by typing a lot. But if you had been doing primary research instead of spending so much time in the forums, there would be no need. I know, I know. You've been doing it all for a hundred years, you're the biggest stick in the EV universe, and how dare anyone challenge your pronouncements from on high. Well, if you had been doing your little tin God job and actually learning about them, which yes, does involve mostly cell DESTRUCTION not preservation, does indeed involve some time, and is of course expensive both in cells and equipment, then I would neither be making such a splash or need to. I've actually been drawn off into this topic much farther than I foresaw or wanted to. We are literally beseiged with requests for MORE of this info, because there are a LOT of people out there quietly LOSING cells following your misinformation, spending THOUSANDS of dollars on BMS systems that don't do shit and in many cases are damaging both batteries and cars. I am stunned that they do NOT want to talk about it in your forums because they are EMBARASSED that they have lost cells, and it must be something THEY are doing wrong. I am getting literally HUNDREDS of these e-mails from people in this situation, whom you have gravely damaged in a very dollar denominated sense, with your nonsense.
I don't mind embarrassment at all. And for a very simple reason. I only learn by failure. Every time I've ever done anything right, or that worked out successfully, I've always wondered what parts I could have left out and it still worked? Every time I've failed at something, I can pretty much come up with EXACTLY what caused the failure. And after a sufficient serial number of years both succeeding and failing, I've learned that the only value anything has is in the failure mode. Once it works, I'm completely disinterested.
So I don't CARE how long your cells have lasted. If it is working for you and you are having a good time, do it till the sun don't shine. You can weigh down your car with $120,000 worth of instrumentation to detect every coulomb passing in the night. But then assuring anyone that will listen that they need to do the same or they will surely lose cells is just nonsense. If you have some real data, generated by actually hurting or killing a cell, that can be duplicated with test equipment, I would be very interested in reading about it. And sure, some of your magic dust and mystical incantations are entertaining, as long as they don't hurt anybody.
Finally, my presence in the EV community is not subject to your approval or appreciation Doc. I am first uncertain that I am in your community, and secondly not too concerned about it either way. I'm not really a "community" kind of guy. We have found a fascinating world of electric cars and batteries and components, and we're having a ball with it. I'm going to publish videos to share what we learn. And if it doesn't match what "you tested" and understand, I don't know what to tell you. I'd like to say I'm sorry but I'm actually not. I don't have any emotion about it at all. Retest. Reunderstand. Do something. I am very pleased with the very surprising response we've had to the videos, apparently they are meeting some need that the forums have not met, and there's a bit of information in that for you I would think. I thought they would be very esoteric and of course very long winded videos of interest to a very narrow group of people who were either intensely interested in the topic or just REALLY hurting for some video to watch. Since our first published video in May 2009, we've just gone over 150,000 COMPLETED video views - that is watched to the end. I don't even know what to make of it. There isn't 2500 LiFePo4 cars on the planet yet.
And yes, I'm here because three of your forum guys tattled on you. I can't type as much as you guys, but as you can see from this message, I can type a LOT when I have to. I don't actually get any smarter when I do it. But I can do it.
Regards;
Jack Rickard
http://EVTV.me