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18650 temperature
#31
(07-30-2019, 01:56 PM)Wolf Wrote:
(07-29-2019, 04:03 PM)OffGridInTheCity Wrote:
(07-26-2019, 02:34 AM)OffGridInTheCity Wrote: Hi folks.  I have 1600+  Panasonic NCR18650A(s) that I'm processing.   I notice that many of them are getting hotter than anything I've encountered so far in my cell processing.

I use OPUS BT-C3100(s).  I discharge at 500ma and charge at 1000ma in a 24C/75F ambient temp environment.  

I generally don't worry about anyting <38C  (100F).    Too hot to touch is obvious discard - e.g. 55C (130F).

However...  what about up to 43C (110F).     Is 43C/110F generally acceptable or what is a 'top heat' that is generally OK?

Does an elevated temperature - up to 43C - indicate that it will get worse over time?  

Any guidance on this would be appreciated.

@AverageJoe said that he's had good luck letting 'heaters' sit a few days and then retest them.    So I gave it a try and it worked.   I had accumulated over 30 heaters and simply restested them - and they all charged/discharged within normal heat range.    Amazing.   Thanks Joe!
OffGridInTheCity,

NCR18650A great battery wish I had that number.
Now down to details.
The NCR18650 is a 3000mAh low drain high capacity cell.
If we look at the spec sheet we find out that the "standard" charge rate is 1475mA with a 59mA cutoff at 4.2V and the standard discharge rate is 600mA to a 2.5V cutoff.

I would be curious to know what the IR of the hot ones is. In my experience with them the IR should be at a max of 45mΩ and a preferred of ≤40mΩ.
You don't mention at what point the cell gets hot. During charging or discharging? As you are discharging at 500mA I would doubt that that is when the heat appears and it is in the 1A charging that it rears its ugly head.
Stressing a battery will get the temp up to 45 °C but that is where I draw the line. Anything above that and in a high drain situation I would not use that battery.
The trick comes in is what are you going to pull from your powerwall?
1A per cell, 500mA per cell, 250mA per cell, or less than that?
I presume all of us are looking for that sweet spot of ~250mA per cell or lower so if we have an average of 2500mAh cells we can run our house for about
10hrs on a full charge. I seriously doubt that "most" reasonable cells will have a heat issue with that discharge rate.

Charging is another matter when the sun is out we want to pump as many amps into the cells as possible. Now that being said let's assume the pack they came in had 12 cells. I doubt very seriously that the pack would be recharged at 17.7 Amps. I could be wrong but I don't think so.

So to answer your question.
Check IR, if possible charge and discharge at manufactures "standard" spec and 45°C is my cut off period.
As far as letting hot ones sit for a couple of days and then try again, If it works great but I would personally put a marker on those cells and treat them as suspect as I have had those cells also Including the NCR18650A and have found out after letting them sit for a month or so they have a tendency to SD.

Wolf

>I would be curious to know what the IR of the hot ones is.
I use 3 x OPUS BT-C3100s and they report a 'general average' of 60-80mOhm for both normal the ones and the ones that overheat.   The big variable seems that many (but not all of heaters) are initially 0.8v-1.1v as I break them out of medical packs.   I read that 50ma charging is 'easier on batteries' till they get up to 3.0v+ range but notice that OPUS does this automatically - so I don't think I'm being that rough on them.
-- I understand that OPUS IR is not 'that accurate' IR wise but its all I have.   My entire powerwall (5,000 cells and counting) was done with these OPUSs - and had routinely been 80-120mOhm IR accross the various battery types.   I haven't really focused on IR they way you have - so I'm sorry that I cannot be more precise.


>The trick comes in is what are you going to pull from your powerwall?
Agree.  My max charge is 333ma per cell.   My max discharge is 690ma/cell but I'm only running about 40% of that - so 300ma/cell right now.   

For OPUS battery certifications, i use 1000ma charge (to hurry the process) and 500ma discharge because I could never get my OPUS to keep running if turned it up to 1000ma.   As it turns out - 500ma discharge is actually representative of my system and I stick with it because I've used that from the very start.  

>Check IR, if possible charge and discharge at manufactures "standard" spec and 45°C is my cut off period.
Thank you for the guidance.  Yes, I'm wary of 'anomalies'.    I also notice that these 'heaters' - a few them throw their CID later on, even when not getting hot.   
Just as a topic, I don't understand why some cells would get hot one day - and be OK a few days later - and throw CID a few days later while charging, even though not hot.  What the heck is going on with these things?.
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