The problem with the Sanyo heaters is much discussed, butin my opinionone 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 isthe "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 mainlythe same as wolf used.
So lets begin with my results:
Average relative IR:
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 wellcan I detect heaters with optimalIRas 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 recognized1as heater. So its a failure rate of about 9%.
This is a very good result !!!
How wellcan I detect heaters with 55mOhm as fixedcriteria?
The prediction:If the measured IR is greatern than the 55mOhmfrom 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 cellswith smaller IR thanoptimalIRnon 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 1as non-heater. So its a failure rate of about3%.
Conclusion:
There is a strong correlationbetween theoptimalIR criteria of Wolf and the rate of heaters. Buthow canI use it practically in my harvesting process?
First check the IR and throw cells with IR greater than optimalIR to the bin or check them verycautious by charging.
Then you can start the capacity test.
Whilecharging 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 willend 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 verygood chance to detect all heaters. Also it's not 100%
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 isthe "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 mainlythe same as wolf used.
So lets begin with my results:
Average relative IR:
- The relative IR (measuredIR /marginalIR) for the heater cells 1.022
- The relative IR for the non heater cells: 0.789
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 wellcan I detect heaters with optimalIRas 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 recognized1as heater. So its a failure rate of about 9%.
This is a very good result !!!
How wellcan I detect heaters with 55mOhm as fixedcriteria?
The prediction:If the measured IR is greatern than the 55mOhmfrom 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 cellswith smaller IR thanoptimalIRnon 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 1as non-heater. So its a failure rate of about3%.
Conclusion:
There is a strong correlationbetween theoptimalIR criteria of Wolf and the rate of heaters. Buthow canI use it practically in my harvesting process?
- As alone pre detection method for heaters?If you just use this criteria you will detect the most of thembut you willnot detect all heaters. So I would not recommend this. You dont want to have a single heater in your powerwall.
- As alone pre detection method for non heaters? It's the same problem, you might predict one wrong and so you end up witha heater in your powerwall.
First check the IR and throw cells with IR greater than optimalIR to the bin or check them verycautious by charging.
Then you can start the capacity test.
Whilecharging 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 willend 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 verygood chance to detect all heaters. Also it's not 100%