Unplugged M3 SR+ overnight in -35C temperatures

[tarndt]

My first post, and apologies in advance if this is a dumb question, but I've been searching for weeks trying to find an answer and have continually come up short.

My wife works shift-work at a hospital and I'm curious what her experience would be like if she took the M3 for a night shift in say a worst case scenario of an Ottawa -35C. Assuming she left with a 90% SoC (~361km in ideal temperatures). She drives about 20 km to work and then would need to leave the car parked for about 13 hours unplugged. When she returns to the car the following morning, is she going to have the mileage remaining to get home (~20km). Heat would be on both ways and it's not during rush hour so the commute would be about 20 minutes each direction. Assuming she would be best to pre-condition the car before leaving?

Any feedback or similar scenarios appreciated in advance.

 

[camalaio]

While you're waiting for a better answer, I'll give some of my own experience and what I've gleaned in other posts on this forum.

A battery sitting out in -35C will probably provide extremely little power or regen when you first start driving. It'll be sluggish.

In addition to the sluggishness, you'll likely have a significant portion of the battery capacity "locked out". I don't know how much this would be, but I recall a post somewhere that I think was -25C and they were still driving around at 26% or something like that.

Still best to precondition if for no other reason than a -35C car is too dang cold! Note that the car must have a reliable cellular signal in order to be reachable with the app and start heating the cabin. If parking underground, it might not work.

Driving in -20C, I found that my energy usage was double that of the rated amount while driving at 60km/h. Driving faster would've made this a bit better, but impossible given the conditions.

What I don't know is if the car tries to keep the battery warmer than -35C and would use power all night to do so. Hopefully someone else can chime in with that info.

EDIT: If it gets that cold, does her workplace not have outlets for block heaters?

 

[pdp1]

IDEALLY, driving 40km will only be about 10% of the battery, so she SHOULD have 80% left. But obviously, driving an EV isn't ideal in cold weather, so lets bump that down to 70%, i.e. double the expected energy needed to drive 40km. 70% of the SR+ battery is about 37.8kWh. Divide that by 13 hours, and you get enough energy for around a 2.9kW consumption rate during those 13 hours. That should be plenty for whatever the car needs while parked (heating/sentry/preconditioning/etc..), as long as you don't have the heater running full blast the entire 13 hours or something else crazy like that.

P.S. I'd probably be more worried about frozen door handles, mirrors, wipers... though preconditioning the car in a timely manner before driving will help

 

[ewoodrick]

Aren't there engine block plugins at that temperature?

 

[tarndt]

Thanks @camalaio and @pdp1 (especially for the preconditioning tip with door handles. It's not often that cold (maybe once or twice per year), I was more curious about the edge case. More likely it will be -15 to -25. I don't think there are block heater plugins in the parking lot but I'll get her to have a look.

Waiting impatiently...

 

[LongRanger]

It’s a good test case as if you compare to a diesel vehicle, at around -13 to -15 Celsius I have had the fuel starting to freeze/congeal and car refusing to start

If the car copes with what you describe that is pretty damn good.

 

[GtiMart]

As Camalaio says, preheat the car before leaving. You'll also heat up the battery and maybe get some regen for the ride. Count a good double consumption for relatively short distances like that. 20 becomes 40, times 2 to return home for 80. Hey, make that 100 just for safety. That leaves you with 261km. Preheating will cost you, 21 minutes this morning at -20C cost me 22km. I have an Awd, yours will consume less so will take more time to heat if its its rwd. Heck, count 50km on each side, although you should preheat at home while plugged. You would still have 161km in the "tank". My last night's sleep took around 1.5km/h (at -20C). At 13h it eats up 20km. Still 141km left. Say there's an idle period before the sleep. That looks like 2.x km/h so a bit more per hour than sleep. Even if it's a bit worse at -35C I can't see how you would run out of power. Don't leave climate on while parked, ideally turn off sentry and it looks like you're good.

To me this is kind of a worse case. Anyone want to adjust this calculation?

 

[nayr14]

I see a lot of talk regarding increased consumption and locked out regen/acceleration. The real question in my eyes is how much energy would be lost while the car has to use the motors and pumps to put heat back in the battery while it sits idle.

I'm not sure of the exact minimum temperature, but using Scan My Tesla I've seen min-temp active heat set at ~-6c. When the pack is around that temp, the motors will run to generate heat and the liquid coolant will run across the heatsinks and into the battery to keep it warm enough not to destroy all the cells. The question is, how much energy will that take over 13 hours?

As others have mentioned, before leaving the house try to pre-condition the car for at least 20 minutes. That runs the rear (and maybe front?) motor to heat the coolant and will attempt to bring the battery up to ~20c. Due to the mass, it will hold its temperature for an hour or two while idle very cold conditions before it needs to heat the cells again.

I don't think you'll encounter issues if the car is 70% before leaving, but please report back and let us know how much energy is lost between when your wife arrives at work and when she departs, as well as the ambient temperature. Those data points would be helpful.