Link between Wh/mi and temperature

[hari-bhari]

I have been trying to figure out the link between range and temperature. Obviously the range is decreased with extreme cold. However, is this reflected in decreased total capacity, or is it reflected in higher Wh/mi? In other words, do I expect to see higher consumption per trip reflected in the trip monitor when it's cold outside, or will the consumption remain unchanged and just the total KWh of the battery is lower?

Lately I've been averaging 320-340 Wh/mi with 80% highway driving, but the AM temps have been around 40F and daytime temps around 60F. I didn't really think this was low enough to affect total range. Any thoughts appreciated.

 

[rcabor]

Higher Wh/mi

 

[mswlogo]

I have been trying to figure out the link between range and temperature. Obviously the range is decreased with extreme cold. However, is this reflected in decreased total capacity, or is it reflected in higher Wh/mi? In other words, do I expect to see higher consumption per trip reflected in the trip monitor when it's cold outside, or will the consumption remain unchanged and just the total KWh of the battery is lower?

Lately I've been averaging 320-340 Wh/mi with 80% highway driving, but the AM temps have been around 40F and daytime temps around 60F. I didn't really think this was low enough to affect total range. Any thoughts appreciated.

Most of the loss is from added load on the battery for the cabin heater.

You do lose some regen. But if you have some regen and on the highway (no traffic) the impact of low regen is really low. It’s around town or in traffic where you need to make more unplanned stops that the lost regen has a bigger impact.

You might lose capacity ( range ) if you see a snowflake. But that should get restored as the battery warms up.

 

[AlanSubie4Life]

but the AM temps have been around 40F and daytime temps around 60F. I didn't really think this was low enough to affect total range. Any thoughts appreciated.

You are talking about two things. 1) The displayed battery capacity in rated miles as a function of temp. And 2) your Wh/mi dependence on temp, due to heat use and other factors.

For 1), at these temps, the effect is pretty small. I have seen a loss of about 6 miles out of 270 available (available rated miles changed but SoC % did not change from about 90%) for a battery left overnight at 35 degrees but it was not even showing a snowflake. AM temps above 40 may reduce max battery capacity a bit but it won’t be huge. I think if the battery really cold soaks to 40 you may see a snowflake but it won’t last long and any energy “missing” will come back.

For 2):
A) air density is higher which increases drag component linearly with density.

B) tires tend to be less inflated unless you are careful

C) The battery internal resistance may be a bit higher. And drivetrain might be a bit more viscous if it is cooler (initially).

D) Loss of regen. Pretty small effect unless you are driving somewhere hilly.

E) Accessory use. Heat can use up to 7kW initially but will settle to a lower number (a few kW)after warming the cabin. AC can use use 1-2kW. Battery heating (not relevant at your temps) can use 7kW or so, but I think typically it does not run when driving unless you are navigating to a Supercharger.

To determine effect (adder) of these, take the average kW of these accessories (you won’t be able to determine this) over your trip duration and divide by your average speed:
watts / mph = Wh/mi

 

[DirtyT3sla]

TeslaFi will automatically chart this for you. I'd like to make a video about this eventually, but here ya go

But it's reflected in increased wh/mi. If your battery is so cold that you can't access all the energy (reduced kWh), your battery will be partially blue with a snow flake. As you drive, that goes away and more miles are unlocked.

 

[hari-bhari]

Very helpful, thanks for the answers.
I am also draining about 5% over 8 hours with an ambient temp of 55F. Is that normal? Sentry is on but not recording any events.

 

[AlanSubie4Life]

Very helpful, thanks for the answers.
I am also draining about 5% over 8 hours with an ambient temp of 55F. Is that normal? Sentry is on but not recording any events.

Normal. Sentry uses 19-24 miles (which is 6.5%, or 10%) per day depending on vehicle type. The SR+ uses 10% per day and LR 6.5% per day. A bit over 200W.