Marktm wrote: ↑
Tue Jun 23, 2020 6:27 am
My "Lizard" pack data plots show a marked "cycle" (in Houston, TX) of amphour capabilities during winter to summer months. I do have some pack temperature data, but basically the pack ranges from in the 60-70 degree Fahrenheit at the end of winter to in the 90s at the end of summer. I never QC, so charging is 3.3kw max. I don't rag the car very often (it is a little go cart!) and I keep in a garage and out of the hot sun mostly. Does this corroborate your observation of keeping battery temps (Tesla) at some optimum between life expectancy and range?
First of all, the temperature dependence of those values is more an artefact of the BMSes ability to accurately gauge capacity, internal resistance and thus come to an SOH value. It seems like the SOH value we're reading out (0x7BB group 61 byte line 10 byte 6-7) is some sort of 'effective capacity' (i.e. usable capacity) value, not the actual SOH as AESC defines it in the datasheet. This obviously varies with average temperature; at higher temperatures, li-ion cells naturally have a slightly higher voltage so you gain a little bit of capacity at the bottom of the discharge curve. Likewise, lower internal resistance will make the pack seem better. There are some nonlinear temperature effects that will make all batteries seem better in most respects at higher temperatures.
Keep in mind that Leaf Spy calls these things SOH, Hx, GIDs, but all of that is names we gave to just a very few data values in the pack's engineering data. Well, okay, GIDs are correct, we know that from Nissan's documentation now, but Hx is just one of at least 8 different health-related values in that response group.
I have SOH, Hx, GIDs and pack voltage data at same points as this Ah graph, would that data be of any help in establishing Leaf's "buffer" analysis for the Lizard chemistry.
I'm not at present doing anything with this data and won't be for a while. Obviously more data is more better, and an effort to centralize this kind of data will yield interesting results. It's not going to be my research though.
BTW, have you seen any pragmatic pack temperature modulator systems (likely during charge sessions - in my garage) that could be installed on my 2012 Leaf? (Other than a window a/c with a heater strip blowing under the battery
Any kind of external thermal management of the Leaf battery is going to be hampered by the piss-poor thermal conductivity of the shell. You have to establish very large temperature gradients to transfer enough heat into or out of the battery that way, and it's going to be distributed anisotropically within - possibly exaggerating the thermal issues these batteries have already. Obviously I'd love to engineer and sell something that you can just slap on and it works, but - pending internal design efforts being done right now - I don't think that will be worth it.
<span>To follow on MarkKtm's comments, for those of us in northern climates, who don't go on long trips or QC, battery temps may never exceed the low 90's which would suggest we should see a similar cycle to what a Bolt or Tesla might see. Especially since Tesla will bring cells up to close to 60C at times. </span>
But there's a big difference between the Leaf battery heating up to near 50C and a Tesla pack going to 55C - Tesla's doing it isotropically (i.e. evenly throughout the entire pack) and thermostatically (i.e. they keep it at a fixed temperature on purpose). Leaf packs can be 50C at the rear module stack and 40C in front, which is actually really bad for degradation. Additionally, the Bolt and Leaf cool down the pack right after driving, reducing thermal load where the Leaf stays hot for hours and hours.
Are the NV200 cells different than the Leaf? I had they they just used the same 24/30/40 pack and added some forced air over the pack, which would suggest degradation would be similar to a lightly used cold weather pack, no?
Exact same cells. Degradation is better than any Leaf battery, without fail. Consider how simple and cheap it would have been for Nissan to improve their battery longevity (and reputation) on these cars. The e-NV200 shows the absolute stupidity of their battery strategy.