**mostly copy paste from my post on e-s**
For those who are not aware, I have acquired (http://endless-sphere.com/forums/viewtopic.php?f=9&t=67661) a full Model S battery pack, that's basically in new condition. I have disassembled the pack and removed individual cells.
For your pleasure, here are individual cell test results Tesla Model S cells, using a 4-wire programmable DC load; cell was charged to 4.20V with a 50mA cut and let to rest for 45 minutes.
I included a common e-bike cell, a new(from fast-tech) Panasonic NCR18650PF (which is rated for 10A cont.) as a comparison. The PF is a very similar cell with the same chemistry with probably only minor differences in electrolyte additives and separator structure.
(My annoying DC load stopped the 10A run at 2.9V for some reason, so I added some extrapolation [dotted line] based on prior tests to 2.5V.)
During the 10A run, I reduced current to 3A for 83 seconds to allow the cell to cool a bit. I did this to point out a couple of interesting, and quite useful performance characteristics of these cells:
-DCIR falls significantly at higher temperatures. This helps to self limit thermal build up of the... as the cell heats up, it tends to actually produce less heat!
-Panasonic NCA cells exhibit significant "surface discharge," that is, they perform well in bursts, where DCIR is lowered for a short period of time after a rest.
Here is a zoom of both effects:
-These cells would run great if bursted to 15A for ~5 seconds, we're talking nearly 50W from this tiny, very high capacity cell.
-Because they are so dense, they have ~350% of the energy capacity per volume when compared to LiFe cells, yet they can still compete fairly well with LiFe cells on a power/volume basis.
I would rate these cells at up to 10A continuous, for up to 12 minutes at a time from full charge, then reduce current to prevent overheating.
- - - Updated - - -
Now, here is a torture test on the cell that I ran (by accident):
I set up another 3A discharge on the cell I had just run at 10A to see how it held up.
It actually picked up even more capacity! However, in addition, my DC load decided this time to not shut off. Not only did it over-discharge below 2.5V, it kept going to 0V, and kept pulling current at 0V for three more hours!!:
The voltage reading is a separate 4-wire voltage sense, so the cell voltage was really reading 0.010V or less. Now my DC load isn't good at measuring very low current, which it was pulling once it hit 0V, so it reality, it had pulled a little more then shown... maybe 3.35 - 3.4+ Ah.
Surely this cell is now trash? That's what they say about cells over-discharged this badly - dispose of them safely. Good thing it wasn't a HK Lipo in my living room...
Finally, after 3 hours it had shut off, and 10 hours after that, and the voltage of the cell had recovered on it's own to 1.8V
So, I decided to give it about 20mA for a while, bumped it up to 50mA, stopped a few times, and eventually charged all the way to 4.2V proper. The cell seemed ok. Held a charge, no self discharge, no heat, nothing:
Now, surely the cell was damaged in some way... maybe the capacity was severely reduced, or DCIR would go way up...
Holy crap, I was right about the durability of the cells!! It lost only ~1% capacity, and after going to 2.55V, it recovered to 3.32V, telling me it had a little more in it, too.
That sure does make me feel a little better about taking them all the way to 2.5V under normal usage....
Stay tuned for a whole suite of torture tests..
I also have an 8-channel automatic programmable cycle tester now that I can use to do cycle testing of the cells.
For those who are not aware, I have acquired (http://endless-sphere.com/forums/viewtopic.php?f=9&t=67661) a full Model S battery pack, that's basically in new condition. I have disassembled the pack and removed individual cells.
For your pleasure, here are individual cell test results Tesla Model S cells, using a 4-wire programmable DC load; cell was charged to 4.20V with a 50mA cut and let to rest for 45 minutes.
I included a common e-bike cell, a new(from fast-tech) Panasonic NCR18650PF (which is rated for 10A cont.) as a comparison. The PF is a very similar cell with the same chemistry with probably only minor differences in electrolyte additives and separator structure.
(My annoying DC load stopped the 10A run at 2.9V for some reason, so I added some extrapolation [dotted line] based on prior tests to 2.5V.)
During the 10A run, I reduced current to 3A for 83 seconds to allow the cell to cool a bit. I did this to point out a couple of interesting, and quite useful performance characteristics of these cells:
-DCIR falls significantly at higher temperatures. This helps to self limit thermal build up of the... as the cell heats up, it tends to actually produce less heat!
-Panasonic NCA cells exhibit significant "surface discharge," that is, they perform well in bursts, where DCIR is lowered for a short period of time after a rest.
Here is a zoom of both effects:
-These cells would run great if bursted to 15A for ~5 seconds, we're talking nearly 50W from this tiny, very high capacity cell.
-Because they are so dense, they have ~350% of the energy capacity per volume when compared to LiFe cells, yet they can still compete fairly well with LiFe cells on a power/volume basis.
I would rate these cells at up to 10A continuous, for up to 12 minutes at a time from full charge, then reduce current to prevent overheating.
- - - Updated - - -
Now, here is a torture test on the cell that I ran (by accident):
I set up another 3A discharge on the cell I had just run at 10A to see how it held up.
It actually picked up even more capacity! However, in addition, my DC load decided this time to not shut off. Not only did it over-discharge below 2.5V, it kept going to 0V, and kept pulling current at 0V for three more hours!!:
The voltage reading is a separate 4-wire voltage sense, so the cell voltage was really reading 0.010V or less. Now my DC load isn't good at measuring very low current, which it was pulling once it hit 0V, so it reality, it had pulled a little more then shown... maybe 3.35 - 3.4+ Ah.
Surely this cell is now trash? That's what they say about cells over-discharged this badly - dispose of them safely. Good thing it wasn't a HK Lipo in my living room...
Finally, after 3 hours it had shut off, and 10 hours after that, and the voltage of the cell had recovered on it's own to 1.8V
So, I decided to give it about 20mA for a while, bumped it up to 50mA, stopped a few times, and eventually charged all the way to 4.2V proper. The cell seemed ok. Held a charge, no self discharge, no heat, nothing:
Now, surely the cell was damaged in some way... maybe the capacity was severely reduced, or DCIR would go way up...
Holy crap, I was right about the durability of the cells!! It lost only ~1% capacity, and after going to 2.55V, it recovered to 3.32V, telling me it had a little more in it, too.
That sure does make me feel a little better about taking them all the way to 2.5V under normal usage....
Stay tuned for a whole suite of torture tests..
I also have an 8-channel automatic programmable cycle tester now that I can use to do cycle testing of the cells.
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