Submitted by Fuzzball on Thu, 2019-11-14 07:27
This is a new post as my prior post was incoherently written in sleep. Let me ask differently now that I am awake and realize what confusion i caused.
- We know that regenerative breaking is limited in 2 states. State of Charge over ~93% and separately due to low temperatures
- Traditional arguments for limited regen at SOC vary, but cover grounds from efficiency to whether voltages can exceed safe levels in high state of charge + high voltage from regen process
- What i am looking to understand is the limited regen in low temperature which seems less understood. What do we think is the key factor in limited regen? All we know for certain is that the limitation is a software limitation - but why?
- Cold Battery has been stated as a common reason: I personally find this hard to believe as limiting factor. If i can plug a cold car to supercharger and battery accepts that, the regen power cant be that much higher. I think estimates on regen peaks put the max around 60kw but normally lower
- So what i am looking for is a non-battery reason for the limitation on regen braking in cold and seeking input if other have observations/prior learning/thoughts about whether the low temperate regen is related to limitations of motor, inverter or other mechanical parts, etc.
- Separately, I have reversed back to the roll mode from hold mode. I suspect that in cold weather, there is too much traditional braking at lower speeds as regen cant be that effective at very lower speeds (have to overcome internal fixed losses before regen is a net positive). Hold mode seems to be more stylistic than related to real efficiencies. However, the other reason I am reverting back is to test regen (without brakes) and see if i can reduce the time it takes for regen braking to step up by utilizing it more