Reviewed logs from over 100 vehicles with 85 packs on recent firmwares over the past several months.
Pumps run because the contactors are engaged because the DCDC is called for by the gateway because the 12V voltage is too low. There was a change to the firmware sometime in 2019 that "mitigated" the weak 12V issue (ie, making it less likely to need to be replaced despite being weaker than normally permitted) by lowering the 12V float voltage once 12V capacity got lower than normal, which limited the amount of time the car can sit with the DCDC disengaged. For the DCDC to be engaged, the battery loop pump has to run since the DCDC coolant is in parallel with the battery pack (lookup the diag screen thermal screenshots).
TL;DR - Pumps running have nothing to do with the HV battery range loss issue or any other safety issue and everything to do with Tesla not replacing 12V batteries as often.
While trying to follow your conclusion here... let me try a walkthrough if I got it right:
Example A - Or: Why the Wallbox will keep max range available.
- I am coming home and plug in my S85 into my Type2 11kW AC Wallbox, leaving and locking, the IC and CD going dark.
- While the charging commences, the 12V battery is drained until the next 12V charging cycle starts, hits the threshold and the 12V discharge/recharge cycle goes on.
- When charging the car overnight to e.g. 70%, 80%, 90% or even 100% is done, the car will still use the external AC to provide energy to run the cars systems so there is next to no HV battery drain despite the running systems.
Example B - Or: Why the UMC will not prevent HV draining.
- I am coming home and plug in my S85 into my UMC v1, then leaving and locking up, the IC and CD going dark.
- While the charging commences, the 12V battery is drained until the next 12V charging cycle starts, hits the threshold and the 12V cycle goes on.
- When charging the car overnight to e.g. 70%, 80%, 90% or even 100% is done, the car will stop using the external AC and start using DCDC to provide energy to run the car systems when the 12V battery voltage runs below a certain threshold thus coolant pumps are running and some HV drain.
- The amount of time used to charge to e.g. 100% is significantly longer, thus keeping the system active and discharging the 12V battery. A "worn out" 12V battery will not provide the same amount of energy/voltage thus resulting in longer 12V charging from DCDC thus leaving the coolant pumps running longer.
Countermeasures in order to reduce coolant pump activity while keeping range:
- Checking/replacing the 12V battery even if no warning is displayed should result in less 12V charging from the HV and less coolant pump activity.
- Use a Wallbox to lower the impact of recharging the 12V while coolant pumps are running, thus having max range available at the cost of some wear and energy usage from the grid/pv.
- Connect an external 12V charger which essentially keeps the 12V voltage high enough even at high SOC thus the GW will not request 12V charging from the HV and car can even go into Energy Saving Mode. This way you can leave the car unplugged and having next to no range loss "overnight". Or you charge with the UMC while having next to no range loss "overnight" after charging is done.
What do you think?
BR! Oaito.
PS: Well, seems to be a case of coincidence rather than correlation, perhaps I'm giving the engineers to much credit. On the other hand, their software solution to countermeasure and limit the "Condition Z" was called to be ingenious by yours truly, given that perhaps the "additional" coolant pump usage while charging 12V and discharging the HV is a hidden benefit?
PS2: A couple of years ago some smart guy took the liberty to explain way less smart guys like me how our brain is wired to see patterns and/or significance even when there is none - it is simply how our human brain is functioning after survival strategies were kind of engraved into our brain pathways. I recall he used some seemingly incredible "news" popping up during some Formula1 training session, whereas two drivers had lap times only milliseconds apart - the news was like: What are the odds! And the smart guy pointed out the odds to come so close was similar to any other variation +/- a couple of seconds. We just are wired to see a significance in the small difference, not because there actually was any. Which brings me to us owners, carefully and somewhat suspiciously looking into the behavior with every new f/w. Finding patterns and significance were there is simply coincidence. Thanks for sharing your findings!