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Hot 40C summers what should max SoC be?
- Thread starter Quickst
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shahryaran
Member
I wouldn't worry about it. The car manages the temperature of the battery pack, and the battery pack has enormous thermal mass so a the difference between a 30C day and 40C day in terms of the heat that will soak into the battery isn't huge.
E90alex
Active Member
Whatever is the minimum you need to use the car without extra hassle or risk of running dead. Same goes for any temp.
If you use 20% of battery a day then a 50% charge limit is more than enough.
If you use 70% a day then you’ll probably need to charge to 80-90%.
If you use 20% of battery a day then a 50% charge limit is more than enough.
If you use 70% a day then you’ll probably need to charge to 80-90%.
Max Spaghetti
Member
Huh? The car doesn't cool the battery pack while sitting parked on a hot day. It might cool the cabin if you have that feature turned on, but not the battery. Yes, it has thermal mass, but will still heat up over the course of a 40C day (as will a 500L water tank). It doesn't take the cabin long to hit 40C in the sun even on a 30C day, (I know, because it tells me every time), and the cabin sits right on top of the battery. And that thermal mass it does have works against you keeping the battery warm into the evening.
Studies linked on this forum show that degradation increases with temperature, and decreases with SoC, particularly at higher temperatures. So the simple answer to the OP question is surely "keep your SoC as low as is convenient for your planned (and potentially unplanned) driving, particularly during hot weather". A sweet spot has been shown at 55% for NMC/NCA and 70% for LFP - these sweet spots seem to be consistent regardless of temperature, but the degradation increases with temperature. So at higher ambient temps the benefit of a lower SoC becomes more significant.
Having said all that, it would be interesting if a study has been/will be done attempting to identify if there is a difference in real-world degradation that can be grouped into climate areas, as well as charging habits. For example, QLD vs VIC, or Canada vs southern USA.
45C might be optimum for supercharging or high battery drain operations which requires high speed battery chemical reactions, but maybe not when battery is quiet?
I know that scheduled preconditioning only raises temp to mid 20C.
The car won’t allow less then 50%,and those of us that have looked into this adequately stay around 54-55% until a trip arises that needs more. Personally when it gets really hot I drop to the 50%, but that’s splitting hairs.
Max Spaghetti
Member
Optimum for what?
45C may be the temperature at which the pack will be allowed to charge at maximum rate (kW), but it most certainly isn't the optimum temperature to minimise long term degradation. Pack longevity is achieved with a combination of low SOC and low temperature.
Pre-conditioning for supercharging (heating the battery) is all about minimising your wait time at the supercharger. The vehicle has an algorithm based on science and testing that will progressively limit the charge rate of a colder battery to prevent damage occurring during charging (same also for regen braking - at colder battery temps it will limit the level of regen available). Chemical reactions in general happen more readily at higher temperatures. Charging a battery involves splitting Li ions from a Lithium Metal Oxide cathode. They have worked out that doing this fast but nicely without too many other unwanted adverse (damaging) chemical reactions that 45C is the sweet spot. Go above 55C and unwanted stuff happens. Charge too fast at cold temps and dendrites start forming. High discharge rates also benefit from higher temps, to a lesser extent, but that is largely irrelevant for day-to-day driving.
There is no need to raise the battery temp when slow AC charging (unless approaching freezing temps), but it helps with fast DC charging. However when you are not charging, low temps reduce the parasitic processes that cause long-term degradation, as does low SOC. Letting a battery sit at high SOC + high temp is best avoided.
The 500L tank isn't going to get to 40C though, particularly since a 40C day means the ambient air temperature might have hit that for an hour or two.
The cabin heats up quickly, to well above the ambient air temperature, because it's got a very low thermal mass and it's directly exposed to that 5500C radiator in the sky. Just parking it under a car port makes a big difference.
Your battery isn't exposed to the sun - it'll only be absorbing heat conducted from the 40C cabin, the air around it or radiated by the surface it's parked on.
Temps we can't change but SOC we can. How high is high
Eventually the heatsoak will cause the temps to rise to an new summer equilibrium. Its a pity there is no easy way of determining the battery pack temp or voltage for that matter
Last edited:
RichardV
Member
There is. Go to service mode. Select software in main menu. Hold and press Model 3/Y text/graphic. Enter service for 'password'
Select lighting bolt, then charging. Show min and max temperature of HV battery.
Yeah, thats a lot of steps though but i get your point
Pity it is not on the screen under a "Battery section"
RichardV
Member
There are multiple battery sensors. It is the instantaneous max and min of all of the battery temperature sensors.
If you want to see target temperatures you need the CAN interface and a CAN reader. ~$130, maybe less now, for such a setup. This will also give you instantaneous cell voltage min/max and overall pack voltage along with a number of data measurements. Battery kwh full and remaining etc, from what the BMS estimates.
Max Spaghetti
Member
Intuitively they would be the real time minimum and maximum temps of all the different temp sensors in the battery right now (not an average or a target).
i.e. currently the coldest part of the battery is 26.25C and the hottest part of the battery is 27.75C.
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