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Sanyo Heater Prediction Routine
#1
The problem with the Sanyo heaters is much discussed, but in my opinion one thing is clear:
You dont want to have a single heater in your powerwall, it's simply dangerous. 

Wolf has developed a criterion based on the internal resistance of the cells, which I would like to verify with my own data and give you an advice how to actually use it. In his "Harvested Cell Analysis -> IR by Part#" Google Table are 2 IR Limits for a lot of known cells listed. One is called "optimal IR" and one is called "marginal IR", optimalIR < marginalIR and so optimalIR is the "harder" criteria.
I checked both criteria with my own database which contains actually 41 Sanyo cells from which are 11 Heaters. The Test setup is mainly the same as wolf used.

So lets begin with my results:

Average relative IR:

  1. The relative IR (measuredIR / marginalIR) for the heater cells 1.022
  2. The relative IR for the non heater cells: 0.789
This looks very promising, the heater cells seem to have a much higher average relative IR. But how accurate are the single criteria?



How well can I detect heaters with marginalIR as criteria?

The prediction: If the measured IR is greatern than the marginalIR from wolf its a possible heater.
Of my 11 cells, I wouldn't have recognized 4 as heater. So its a failure rate of about 36%. Thats to bad for using it as a detector.


How well can I detect heaters with optimalIR as criteria?
The prediction: If the measured IR is greatern than the optimalIR from wolf its a possible heater.
Of my 11 cells, I wouldn't have recognized 1 as heater. So its a failure rate of about 9%. 
This is a very good result !!!


How well can I detect heaters with 55mOhm as fixed criteria?

The prediction: If the measured IR is greatern than the 55mOhm from wolf its a possible heater.
Of my 11 cells, I wouldn't have recognized 3 as heater. So its a failure rate of about 27%. 


Are all cells with smaller IR than optimalIR non heaters?
The prediction: If the measured IR is smaller than the optimalIR from wolf its non heater.
Of my 30 non heater cells, I wouldn't have recognized 1 as non-heater. So its a failure rate of about 3%. 

Conclusion:
There is a strong correlation between the optimalIR criteria of Wolf and the rate of heaters. But how can I use it practically in my harvesting process?

  1. As alone pre detection method for heaters? If you just use this criteria you will detect the most of them but you will not detect all heaters. So I would not recommend this. You dont want to have a single heater in your powerwall. 
  2. As alone pre detection method for non heaters? It's the same problem, you might predict one wrong and so you end up with a heater in your powerwall. 
So what to do?
First check the IR and throw cells with IR greater than optimalIR to the bin or check them very cautious by charging. 
Then you can start the capacity test.
While charging your cells, do your standard testing by measure the temperature or just feel with your hands regulary. Of course this is also not a 100% safe method to detect heaters, maybe you just checked the temp in the wrong moment and so you will end up with a heater in your powerwall. But if you use the IR measurement in combination with the "hand checking temperature", you will have a very very good chance to detect all heaters. Also it's not 100%
WuggyBuggy likes this post
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#2
Valid scientific based approach .. Big Grin

... with one flaw:
Quote:Thats to bad for using it as a detector.

That solves 2/3rds of the problem you have, in a simple, time saving and safe way, and reduces the problem to one/third. Big Grin
1 kWp in Test
4 kWh battery target - plus Mobile Home battery
Ultra low cost
Electronics ? No clue. Am machinery engineer.
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#3
(05-03-2019, 08:44 AM)Cherry67 Wrote: Valid scientific based approach .. Big Grin

... with one flaw:
Quote:Thats to bad for using it as a detector.

That solves 2/3rds of the problem you have, in a simple, time saving and safe way, and reduces the problem to one/third. Big Grin
Yes you are right Confused I hoped for an easier solution. But actually its not easy. 
But I also wanted to point out that it is not enough to rely on just one value.
And I wanted to confirm wolf's results.
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#4
(05-03-2019, 07:26 AM)drbacke Wrote: Conclusion:
There is a strong correlation between the optimalIR criteria of Wolf and the rate of heaters. But how can I use it practically in my harvesting process?

  1. As alone pre detection method for heaters? If you just use this criteria you will detect the most of them but you will not detect all heaters. So I would not recommend this. You dont want to have a single heater in your powerwall. 
  2. As alone pre detection method for non heaters? It's the same problem, you might predict one wrong and so you end up with a heater in your powerwall. 
So what to do?
First check the IR and throw cells with IR greater than optimalIR to the bin or check them very cautious by charging. 
Then you can start the capacity test.
While charging your cells, do your standard testing by measure the temperature or just feel with your hands regulary. Of course this is also not a 100% safe method to detect heaters, maybe you just checked the temp in the wrong moment and so you will end up with a heater in your powerwall. But if you use the IR measurement in combination with the "hand checking temperature", you will have a very very good chance to detect all heaters. Also it's not 100%
Very good synopsis and well written up.

In your conclusion I only have some criteria to add.(Not criticism just criteria)  Tongue 

Quote:As alone pre detection method for heaters? If you just use this criteria you will detect the most of them but you will not detect all heaters. So I would not recommend this. You dont want to have a single heater in your powerwall. 

I don't think I suggested that my IR measurements should be the lone means to check for heaters, only that cells that fall within those measurements are most likely not to be heaters. Also a manual or electronic temperature check of any cell esp. the infamous Sanyos should be performed without a question. Additionally if you are using these "Sanyo" cells in a high demand application to be very weary of them. I have charged them at 1A, at 0.5A and at 0.05A and to be honest the "heaters" will show up at any amperage especially when checking them with a thermal camera. A tenth or two of a degree will show up like a lightbulb on the thermal image screen.
These are pictures of all Sanyo cells being charged on a CC/CV parallel board at 4.2V at 50mA. Can you spot the heaters?
We are talking about 1 or 2 °C barely can feel it by hand if at all.


Quote:As alone pre detection method for non heatersIt's the same problem, you might predict one wrong and so you end up with a heater in your powerwall.

Again it is not the lone criteria but a guide to go by.  Your mileage may vary but you will at least be playing in the ballpark. You may get a strike or two but in the long run you will win the game. This was not an exercise in prediction but an exercise in avoidance.
Avoiding cells with a potential of being a heater not predicting cells with a potential of being a heater.


Quote:So what to do?
First check the IR and throw cells with IR greater than optimalIR to the bin or check them very cautious by charging. 
Then you can start the capacity test.

Perfect could not have said it better myself. Smile Smile Smile Smile


Wolf
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If 18 X 650 = 2200+mAh then we have power! 
May all your Cells have an IR of 75mΩ or less Smile
Last count as of 8/7/2019
Total Number of Cells Recorded and processed                 6149
Total Cells required for PowIRwall                                   2856
Total Cells ≥2200mAh, ≥80%, ≥35mΩ, ≤75mΩ, ≥4.12V   2760
For Info Google Drive
Not your average Wolf       
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