so basically what you are saying is that older packs run hotter?
No. I'm saying that older packs tend to have higher deltas on temperature and/or voltage between modules.
I interpret it as a safety after the fires, in case there is a hot spot developing they keep the battery pack temperature equilibrated for a LONG time
Do you have a CAN log with the thermal measurements of the 32 sensors in the pack to back up this interpretation? Any evidence showing a module consistently gaining temperature or otherwise not dissipating thermal energy to the loop as expected?
Sounds like a pretty baseless argument. See below a sensible argument against "hot spots".
[...] then start those fans/pumps that loud and for that long to reduce the SoC.
I like that fans are now being added into the conspiracy theory mix only after I noted that cooling doesn't actually happen on the battery loop while stationary without fans... and it still somehow fits the false narrative despite no one reported fans running, only pumps (at least not that I saw posted before my note about fans)? Interesting...
It just doesn't make sense.
It only doesn't make sense to folks who won't follow the facts and make logical conclusions. Here's a post from someone who gets it:
A "hot spot" makes no sense. If the pack has failed enough that it is developing significant hot spots in the pack, cooling it extra after the car is done charging won't help much. If the hot spot is due to a significant defect such as internal short (which is really the only way a "hot spot" would occur, either you will quickly end up with a severely imbalanced pack which requires replacement, or it will quickly turn into a bigger issue which will trip a thermal fuse or worse when driving around or when charging.
As wk057 has been trying to explain, it's more likely that it's due to a programming change in the tolerable temperature imbalance above a certain cell voltage that should be relaxed.
The amount of delta-temperature permitted, and thus when equalizing pumping is triggered, varies based on SoC and other factors. At higher SoC the permitted delta is lower, and the loop will run to equalize the temperatures across the modules. Super simple.
The "hot spots" conspiracy theory is complete BS anyway. Let's debunk!
First, how would a cell or module develop a "hot spot"?
Let's assume for the sake of argument that this is whats happening, and there is some issue with a cell in the pack that causes it to self heat due to some internal issue (HYPOTHETICAL FOR THIS POST,
NOT SAYING THIS IS THE CASE).
Now, the conspiracy theory in this thread about the pumps running constantly is to somehow prevent this hypothetically bad self-heating unsafe cell from getting too hot by doing... something. The claim so far has been that somehow the pumps running the coolant through the closed battery loop, with no fans going, will magically dissipate self heating in bad cells.
Ok, that's impossible... but, let's accept that there's some magic there... just to give this debunk an even more solid foundation and anchor to reality.
So there's a self heating cell, and somehow we're keeping it cool. But um... where's the energy coming from for the heating? If a cell is self-heating, that energy has to
come from somewhere.
Where would energy for a self heating cell come from? Well... from that cell, and possibly other cells in parallel with it.
How would that show up in diagnostics and empirical data? As a consistent drain on that cell group causing a consistent downward imbalance.
What does Tesla already detect and deal with using the BMS? Unexplained imbalances. In fact, unexplained downward imbalances throw a user facing error to contact Tesla service, and place the car into low power limp mode (initially) and fully disable the vehicle eventually if the imbalance grows too great. (Keep in mind, the BMS can NOT correct an imbalance where a cell group is too LOW on voltage. It can only discharge cell groups to correct an imbalance.)
(Edit: To answer an unasked question, "unexplained"
upward imbalances, where a cell rises to a higher voltage than expected per pack-level charge provided... are generally explained by other factors, such as normal degradation, temperature vs charge rate, etc... Overall, since nothing will push a cell too
high without the BMS saying so, upward imbalances are just corrected by the system without warning or error, unless they are consistent and out of spec.)
Long story short, this latest conspiracy theory, like all of the others being pushed here, is complete nonsense and has no basis in reality. Just a general lack of understanding about how the system works being twisted into some imagined grand nefarious scheme.
Like I (and others) have said, the pumps running are most likely an artifact of an older pack not reaching temperature delta targets as desired by the BMS, and Tesla doesn't seemed to have loosened these targets to allow this in older packs without a constant attempt to balance thermals, thus causes an infinite run of the closed loop while the target delta is programmed to be tighter (based on SoC and other factors). And, from what I can tell, the specifics of this particular algo haven't been changed in years.
