eMark
100 kW
Thanks! Maybe, i got a really good BG-8S or i don't have a good enough DMM ... or, maybe because the comparison was at 3.75V ... anyway close enuf for my scientific notation :wink:
Li-ion cells cycle ageing
- Thread starter docware
- Start date
Nope sorry just not true.eMark said:
I've seen many many packs go thousands of cycles just fine with huge imbalances, many for well over a decade.
So long as you just accept the overall pack capacity is limited by the weakest link (which is unavoidable anyway)
if the top and bottom stop-points are based on the first cell or group to get there, not the pack level voltage
or just calibrate your pack-level stop-points for the same result
then that "dire problem" you are warning about is a complete non-issue.
With "zero balancing ever", or middle balancing, then you will see imbalances both top and bottom, and that is just fine, no need to "do something" about it.
eMark
100 kW
Thanks! Maybe, i got a really good BG-8S or i don't have a good enough DMM or a little of both ... or ... maybe because the comparison was at 3.75V. Anyway close enuf for my scientific notation :wink:docware said:
eMark
100 kW
Padja where are you when i could use your moral supportdocware said:
docware thinks he's talking to a newbie (not my opinion), but what do i know :wink:
How precise is precise enuf? It's not like we need Musk's precision for reading the remote voltages when his Tesla is cruising around on the Sea of Tranquility. Even then +/- 5mV may be close enuf between all the Tesla P-groups IF "P-groups" is still relevant nomenclature by then.
It's my understanding (could be wrong) that most all inexpensive BMSs only discharge balance when voltages between the P-groups is over 30mV. In other words a BMS won't even attempt to balance the P-groups in a battery unless disparity exceeds 30mV between the P-groups. So, how concerned does one really need to be if most all run of the mill BMSs don't even discharge balance unless there is at least a 30mV disparity ??
john61ct said:
No, volmeter can´t be calibrated. In fact, there is no reason as this simple-purpose instrument was built for comparative measuring of the parallel groups. So that absolutely accuracy was not the primary. However, thanks to built-in precise voltage reference, I know that measuring around 4,1 V is pretty accurate.
I don´t see any significant drift, just have to wait cca 8 – 10 minut after switch-on to see that reference voltage is stabilized at 4,0962 V.
eMark
100 kW
You do realize that 0,1mV is actually 0,0001V. It isn't necessary to have a DMM that can read 4 places beyond the decimal point to know "what's truly going on". Scientific notation uses a period (not a comma) and generally three digits (e.g. 3.745V) is sufficient. For the purposes of even this ageing thread it's not necessary to know the cell voltage four digits beyond the decimal point ... as you've implied with "0,1mV" (e.g. 3,7453V). Three digits beyond the decimal point is sufficient for ebiker DIY builds when using a quality DMM and Cell Monitor for checking Lithium-ion cell voltages :thumb:docware said:
Also, glad to see your reference to Li-ion cell chemistry (e.g. NCA & NMC) in a recent post in your excellent thread. As further explanation the reason it's NCA and not NAC is because the recipe called for more cobalt than aluminum. Also the acronym ICR emphasized the importance of cobalt in the recipe which is no longer true. In part because of what some believe is the growing scarcity of cobalt and Nickel's importance. The relevance of Oxide to a Li-ion cell is either expressed as O2 or 04. Apparently 3 letters is sufficient ... so no need for LNMCO :wink:
The reason for N at front is because of its importance in the chemical recipe of NMCs 811 cathode (80% Nickel, 10% Manganese, 10% Cobalt). More recent hybrid recipes include 433 and 532 with 622 being the a more recent NMC recipe. There is still some discussion whether the acronym should be NMC or NCM depending on which ingredient they believe is more important and that depends in part on the application. NCA cathodes typically have 80% Nickel and 15% Cobalt, but are ‘doped’ with aluminium as opposed to manganese.
flippy
1 MW
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- 2,351
eMark said:
you actually do in a lot of cases. if you do lots of measurements that require lots of range you will see lots of limitations with like a cheapo 6000 count meter. i personally have a quite expensive 500000 count meter. so i can have up to mV accuracy with batteries up to 50V and 10mV accuracy up to 500V.
It is simple. If my paralel groups are within 3 mV, resolution 0,1 mV is must for reliable and repeatable measurement. Requirement of ten times better resolution than measured values is valid not only for measurement of electrical values, but for measurement of all physical units generally.
Good news – you don´t need expensive DMM.
Today´s checking against 5 ½ 0,012 % precision DMM GW Instek revealed that this cheap chinese voltmeter is unbelievably accurate. It´s within 0,1 - 0,3 mV through the whole area of interest 2,7 – 4,2 V depending on the time this cheap voltmeter is running. Longer running time (one hour and more) means higher difference 0,3 mV. However, this cheap unit is nearly on par with 5 ½ DMM ! At least in the range 2,7 – 4,2 V.
Good news – you don´t need expensive DMM.
Today´s checking against 5 ½ 0,012 % precision DMM GW Instek revealed that this cheap chinese voltmeter is unbelievably accurate. It´s within 0,1 - 0,3 mV through the whole area of interest 2,7 – 4,2 V depending on the time this cheap voltmeter is running. Longer running time (one hour and more) means higher difference 0,3 mV. However, this cheap unit is nearly on par with 5 ½ DMM ! At least in the range 2,7 – 4,2 V.
eMark
100 kW
Realistically, doesn't that "If" become more of a challenge the more P-groups (e.g. 10S4P vs 14S8P) even with top brand name grade A cells as the battery ages.docware said:
Not disagreeing with the need for precise accuracy when testing cells whether by the manufacturer for their datasheet or by you for presenting in this thread. But here's my rub (if a rub) so would appreciate your take (Yes, No, Maybe with brief reasoning) as it possibly deserves further discussion in another thread. So, here goes FWIW ...docware said:
It's my understanding that even supposedly good enough BMSs (say $20-$30) only discharge balance when the P-groups variance is over 30mV. In other words most all BMS (maybe even smart bluetooth BMSs) don't begin discharge balancing until there is at least a 30mV disparity between at least one of the P-groups and the other P-groups.
If this is true then would you agree that it's a good idea on every DIY build to attach two monitoring-balance leads for at least cell monitoring and discharge balancing. A 14S8P would require two 7S balance leads with one going to each 7S8P. Two leads because there's no reasonably priced cell monitor/discharge balancing feature beyond 8S, (no current duo balance charger beyond 6S). Not only for monitoring P-group cell voltage, but also for discharge balancing and balance charging (if 10S and 12S) when necessary. Especially, if your goal is to maintain no greater variance than say 3mV, 5mV or even 10mV as the battery ages instead of waiting until the BMS begins discharge balancing at a variance greater than 30mV. By then it may be too late. Even then any discharge rebalancing via a BMS is only as good as 30mV P-group disparity ... if in fact that is true with majority of BMSs.
Realize this topic is for another thread, but would at least appreciate whether you think it's a good idea or not necessary to attach two monitor-balance leads (e.g. 2-5S, 2-6S, 2-7S) on a DIY build. According to your above post is it even possible to maintain such close tolerances (3mV) between P-groups on a DIY pack (either before or after charging) without the use of two balance leads for P-group monitoring an discharge balancing as needed? Hopefully keeping the P-groups within 3mV, 5mV or even 10mV as the battery ages as long as possible :thumb:
eMark
100 kW
eMark said:
Is it not a legitimate ageing question? Don't see why you think it's "weed infestation."docware said:
Maybe, it's a dumb question as the answer is probably Yes with the same kind of cells, same application, etc. Possibly something to consider when deciding to build an 8P or 6P for maintaining P-groups within 3mV of each other as long as possible for battery health. Then thinking about it some more thought maybe just the opposite with the advantage going to 8P for longevity (Tesla battery has 96 P-groups). So, maybe the number of P-groups in a DIY battery makes no difference when it comes to whether or not more P-groups can shorten battery life (if that were the only variable) ??
Just want to say i appreciate your quest for precision in this ageing thread. It got me to making comparisons between three DMMs, Capacitor Controller, Tenergy 5-in-1 Cell Meter, two different digital balance chargers, two LVA cell logs and iDST BattGO 8S. Anyway will not post anymore on your thread. Keep up the good work :thumb:
New data : Samsung 30Q 536 cycles, LG MJ1 500 cycles, SONY VTC6 267 cycles, Samsung 50E 216 cycles, Samsung 35E 182 cycles, LG HG2 127 cycles.
Wrong DCIR data LG HG2 at 50 cycles corrected (originally wrongly measured with filter on).
Adding new picture of M36 DCIR with corrected curve ( originally wrong data on 95 % SOC on the page 4 - typo error)
Wrong DCIR data LG HG2 at 50 cycles corrected (originally wrongly measured with filter on).
Adding new picture of M36 DCIR with corrected curve ( originally wrong data on 95 % SOC on the page 4 - typo error)
serious_sam
10 kW
Hi docware, firstly, thanks for this data you generously share with us.
Sorry if I missed it, but did you mention what SOC you perform the IR measurement (for the bar graph @50 cycles) ? Thanks again.
Sorry if I missed it, but did you mention what SOC you perform the IR measurement (for the bar graph @50 cycles) ? Thanks again.
serious_sam
10 kW
Understood. Thanks.
Problem is your questions are often too wordy and just not comprehensible. Besides being needlessly specific and unecessary, argumentative to the point of constituting harassment.eMark said:
e.g. you've already been told it is pointless if not counterproductive to argue against another member's desire for accuracy in their instrumentation, hence the OP's expression of extreme frustration.
Please try to take in this feedback as friendly and constructive, which is my intention here.
_____
In this case I can't tell if you mean "more groups" which would mean, 10S goes to say 14S
or "10S4P vs 14S8P" which is just doubling the # of cells in each group.
The ability to keep the cells well balanced (in this case delta < 3mV) does not change in either case.
goatman
10 MW
the above picture of 30q at about 525 cycles that docware posted. is that about 1900mah? from 4.1v to 3.3v
okashira did a cycle test of 30q and after about 540 cycles at 7 amp discharge it had about 2100mah but his test was 4.15v to 2,8v I think
https://endless-sphere.com/forums/viewtopic.php?f=14&t=68556&start=100#p1148592
do you have the graph of the discharge line for 1 cycle? im just curious if the capacity is starting to drop sharply like a hockey stick or if its still discharging on a straight line.
okashira did a cycle test of 30q and after about 540 cycles at 7 amp discharge it had about 2100mah but his test was 4.15v to 2,8v I think
https://endless-sphere.com/forums/viewtopic.php?f=14&t=68556&start=100#p1148592
do you have the graph of the discharge line for 1 cycle? im just curious if the capacity is starting to drop sharply like a hockey stick or if its still discharging on a straight line.
I also noticed the Samsung 30Q had some dfifference. However the capacity graph on the side states 100% to 80% and is very similar to Panasonic, Sanyo ga, Sony vtc6 and possibly samsung 35e in the future. I have and like alot of cells like Samsung 29E, Panasonic PF. They seem to come in three versions a b and c which say that they are high performance, medium and long endurance cell.
Cells that reach me are
Chinese cells(found out they kind of die straight after 400-800 cycles), Panasonic PF(yah, thanks for all the info)
However one cell I have alot of. That comes in many iterations are Sanyo Red cells. They have many. I get alot of these called Sanyo 18650AA cells with a 4,3A power at 2150mah if I recon correctly.
Another cool cell I'd like to know more about is Sony 18650V3 2150mah 10A capable older type or model of cell if you compare to the newer medium power cells and can be spotted by the lower voltage at load throughout the test in a graph showing in essence less power or area in the graph than newer cells. The are also reflects the total capacity of the cell, this can be fun to know.
Also the first cell I came into first contact with was Panasonic CGR18650 2250mah. Used ones. Pretty weak cell if you ask me(mine were about 1500mah) and I just noticed they commit suicide charged under zero C* conditions ifs cell is higher than 65 m-ohm.(note: https://secondlifestorage.com/showthread.php?tid=1732)
Cells that reach me are
Chinese cells(found out they kind of die straight after 400-800 cycles), Panasonic PF(yah, thanks for all the info)
However one cell I have alot of. That comes in many iterations are Sanyo Red cells. They have many. I get alot of these called Sanyo 18650AA cells with a 4,3A power at 2150mah if I recon correctly.
Another cool cell I'd like to know more about is Sony 18650V3 2150mah 10A capable older type or model of cell if you compare to the newer medium power cells and can be spotted by the lower voltage at load throughout the test in a graph showing in essence less power or area in the graph than newer cells. The are also reflects the total capacity of the cell, this can be fun to know.
Also the first cell I came into first contact with was Panasonic CGR18650 2250mah. Used ones. Pretty weak cell if you ask me(mine were about 1500mah) and I just noticed they commit suicide charged under zero C* conditions ifs cell is higher than 65 m-ohm.(note: https://secondlifestorage.com/showthread.php?tid=1732)
Jan-Erik-86
100 W
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- Jan 23, 2019
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leffex said:
Some studies have shows you can charge below freezing at an extremely slow charge rate, but in practice any liion cell charged normally below 0c will die instantly, regardless of the dcir. This is because charging below freezing causes plating inside the cell.
I have several of those old CGR18650 as well and i noticed they often have a lot of capacity left, but only at a slow discharge rate.
New batch of data : Samsung 30Q 585 cycles, LG MJ1 550 cycles, SONY VTC6 312 cycles, Samsung 50E 258 cycles, Samsung 35E 227 cycles, LG HG2 181 cycles.
Because Samsung 50E got affected by the tester, I have made some trial to estimate how much. Result is aprox 1,7 %, so I made another chart with 50E offset 1,7 % from 150 cycle point in effort to estimate what normal course of this cell woud be like.
Pajda, could you please comment on my attempt ? Do your 50E tests have similar trend of the capacity ?
Because Samsung 50E got affected by the tester, I have made some trial to estimate how much. Result is aprox 1,7 %, so I made another chart with 50E offset 1,7 % from 150 cycle point in effort to estimate what normal course of this cell woud be like.
Pajda, could you please comment on my attempt ? Do your 50E tests have similar trend of the capacity ?
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