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18650 temperature
#11
(03-01-2019, 01:11 PM)allend83 Wrote: Wolf just a quick question, I've heard that charge levels at point of test can affect the IR. Would agree or disagree with this?

Also you make ref to cells >100mΩ not being worth it. Is this just because of the risk of overheating?

Charge level does affect IR but not a whole lot I have found. Take a look at the pretest IR and the IR after 30+ days of rest most cells have a slight drop or slight increase. The exceptions prove the rule. Sheet will explain.



Well no it's not so much the overheating part as more of the performance side. I find that "most" cells over 100mΩ seem to just not have the umph anymore. There are some LGs that seem to hang on for dear life at that resistance but not enough. 

Also when building a 200p pack I would like to keep my resistances as similar as possible, All cells within a 40mΩ to 70mΩ range. I feel a consistent resistance range will just assist the parallel cells in a pack to humm happily together. After all the packs made by manufactures use the same cells in each pack with the same resistance. I haven't pulled a pack apart that has a mix of panasonic, sony and lg mixed together. I mean that is what we are doing so it begs the question do we keep the cell chemistry and certain parameters as close as possible. I think so! At this point I have 1180 cells that meet my criteria. Hope that explains my strategy.


Wolf
If 18 X 650 = 2200+mAh then we have power! 
May all your Cells have an IR of 70mΩ or less Smile
Last count as of 3/22/2019
Total Number of Cells           3679
Cells  >80% of Capacity        2389
Cells <80% of Capacity         1265
Cells ≥2200mAh & ≥ 80%     1653
Google Drive for info https://drive.google.com/drive/folders/1...sp=sharing
Not your average Wolf       
            Cool



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#12
All makes complete sense. I was thinking ohm's law when I was asking you that question. Obviously a cell is a resister in itself hence we are having this conversation about IR. I had seen significant differences between the same cell, full capacity Vs whatever capacity the cell was at point of first charge. Based on your last comment about the Liito-Kala I'm now uncertain how much I can rely on the results that I am seeing. Time to invest in a YR1030!!

This is a minefield!

I can understand your logic in trying to keep packs equal. I suppose this is the reason also why one would also want to ensure equal charge and mah (pack to pack), why would you therefore not want to use this concept with IR, makes sense.

Wolf you have been very helpful, thank you ?

Wolf slightly off subject and just a quick question. I'm finding the Liito-Kala doesn't take the cell to full 4.2v it's suggesting on screen. I've waited watching to catch a cell as soon as it's charged pulling straight out of the charger and testing with multi metre with results ranging from 4.14-4.18v. Have you seen this behaviour with your Liito-Kala?
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#13
(03-01-2019, 02:45 PM)allend83 Wrote: ..... you have been very helpful, thank you ? ......

Wolf slightly off subject and just a quick question. I'm finding the Liito-Kala doesn't take the cell to full 4.2v it's suggesting on screen. I've waited watching to catch a cell as soon as it's charged pulling straight out of the charger and testing with multi metre with results ranging from 4.14-4.18v. Have you seen this behaviour with your Liito-Kala?

Thank you with a question mark? LOL I hope I have not scared you off!

I do find the LiitoKala a little lacking in the V accuracy. Also the charging side may be off also. I have never done a test on that. I did a test on a bunch of V and mΩ readings from different testers a while back though.

I think it would be a good Idea to revisit that chart with my Fluke and maybe expand on it a bit. I will have some results this weekend or maybe possibly tonight.

If you want a jump on the results see if you can get some salvaged nickel strips (from battery packs) and put them between the battery terminals and the LiitoKala's contacts. Get some alligator clips that attach to your DMM that way you can monitor the V and see what the difference is. That is if your DMM is accurate. Tongue


Wolf
If 18 X 650 = 2200+mAh then we have power! 
May all your Cells have an IR of 70mΩ or less Smile
Last count as of 3/22/2019
Total Number of Cells           3679
Cells  >80% of Capacity        2389
Cells <80% of Capacity         1265
Cells ≥2200mAh & ≥ 80%     1653
Google Drive for info https://drive.google.com/drive/folders/1...sp=sharing
Not your average Wolf       
            Cool



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#14
Sorry Wolf I have absolutely no idea where that question mark came from and didn't realise it was there until you mentioned it! Sorry and genuinely you have been very helpful. I did put a thumbs up on my phone maybe that explains the misplaced punctuation mark?

Oh my word so it could also be my DMM, Ahhhhhhhhhhh. What have I started?

I might give that test a go and see what happens?
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#15
(03-01-2019, 03:36 PM)allend83 Wrote: Oh my word so it could also be my DMM, Ahhhhhhhhhhh. What have I started?

I might give that test a go and see what happens?
 You have opened the door and started to go into another dimension in time and space ...................... you have entered

Wolf
If 18 X 650 = 2200+mAh then we have power! 
May all your Cells have an IR of 70mΩ or less Smile
Last count as of 3/22/2019
Total Number of Cells           3679
Cells  >80% of Capacity        2389
Cells <80% of Capacity         1265
Cells ≥2200mAh & ≥ 80%     1653
Google Drive for info https://drive.google.com/drive/folders/1...sp=sharing
Not your average Wolf       
            Cool



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#16
LOL

Wolff I've just had a Samsung ICR18650-26F reach 60°c!!!! Now that must be to hot?
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#17
(03-02-2019, 07:13 PM)allend83 Wrote: LOL

Wolff I've just had a Samsung ICR18650-26F reach 60°c!!!! Now that must be to hot?

That my friend is too hot yes. what does the LiitoKala show for IR?
Where you charging at 1C  (1A) not that that is high. Standard charge is 0.5C  (1300mA).


Wolf
If 18 X 650 = 2200+mAh then we have power! 
May all your Cells have an IR of 70mΩ or less Smile
Last count as of 3/22/2019
Total Number of Cells           3679
Cells  >80% of Capacity        2389
Cells <80% of Capacity         1265
Cells ≥2200mAh & ≥ 80%     1653
Google Drive for info https://drive.google.com/drive/folders/1...sp=sharing
Not your average Wolf       
            Cool



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#18
I'll be honest Wolf I've not been taking much notice of the IR reading from the Liito-Kala because I've been getting massively inconsistent results from them.

I was charging at 1000mAh (1A).

In your opinion when is hot too hot?
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#19
Me personally?

I get nervous if a cell gets more than 40°C but then again I charge at 500mA. On my SKYRC I charge at manufactures standard which is usually 0.5C basically half of capacity. but it has 2 turbojet fans under it so the temp never gets above 38°C.

I have seen specs on cells being discharged at 10A and going to 65°C to 70°C but that was discharge.
I suppose the upper limit would be somewhere near there as cell actually are rated to withstand much higher temps than that.


But the question come down to this. Is this a cell you want in your powerwall or pack or whatever you are building.
I say no. There are plenty of cell that do not exhibit this phenomenon so that's all I have to say IMHO.

Wolf
If 18 X 650 = 2200+mAh then we have power! 
May all your Cells have an IR of 70mΩ or less Smile
Last count as of 3/22/2019
Total Number of Cells           3679
Cells  >80% of Capacity        2389
Cells <80% of Capacity         1265
Cells ≥2200mAh & ≥ 80%     1653
Google Drive for info https://drive.google.com/drive/folders/1...sp=sharing
Not your average Wolf       
            Cool



Reply
#20
I'm thinking of reducing my charge current and have also been contemplating introducing some fans. I was only at 1000ma to speed up the charge. I may be doing my testing arse about face! I charge to full and check for SD, then IR (when yr1030 arrives) and finally capacity.

I've seen specs on cells like that as well. Also some loon on another forum suggested 90°C which quite frankly is eye watering and scares the living hell out of me!

Absolutely couldn't agree more do I want such rouge cells in my build probably not. But assuming IR is not an issue (which I can only assume seeing as I can't test it. At this moment can't think what else could cause a high cell temp other than IR) I'm going to be building a small powerwall so therefore the draw per cell is never going to get anywhere near 1A not at least for a sustained amount of time. Therefore am I worrying un unnecessarily? As I said before minefield!

PS side note where are you based?
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