How Miserable Is A Winter Tesla Road Trip? -18°C & Broken Superchargers

[electruck]

Another great video from Engineering Explained. While he does address the impact of temperature on range, he also spends a significant amount of time discussing charging strategies and the benefits of shorter, more frequent stops to a lower SoC vs longer, less frequent stops to a higher SoC. His trip was in a Tesla Model 3 but his conclusions pretty much apply to all BEVs. I don't think he covers anything that hasn't been discussed around here before (except perhaps how charging more frequently gave him the confidence to drive a little faster) but it is still a very good watch, especially for those who have never owned a BEV.

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[ajdelange]

There are lots and lots of videos out there made by people who basically don't know what they are talking about. This is not one of those guys! He does make the occasional mistake (he's human) but by and large you can accept almost everything he says.

The most important takeaway from this video is that cold weather does not take away half your range. Fifteen to 20% is more like it. The main thing he missed is that it isn't the cold that takes it away. It's the stuff on the road. How much of the footage in the video shows dry roadbed? None - and that's where the extra MPG go, i.e. pushing that water/slush out of the way. The second error is in saying that all the cabin heat comes from electric heaters. At the rates he was driving there is probably a kW of waste heat from motors and inverters. Assuming that the battery warms itself at these moderate levels of cold that kW is available to heat the cabin. It is only when that isn't enough that the electric supplemental heater cuts in and, of course, if you are preheating or maintaining the cabin when the car is stationary. But, of course, some heat is taken directly from the battery to warm the cabin. Were this not the case Tesla would not have developed the Octovalve (which allows the heat pump to extract heat from reasonably cold air).

Why is any of this relevant on the Rivian forum? Because the Rivian is probably going to be the essentially the same in it's cold weather performance.

Now at -40 in a howling head wind on the plains of Alberta? Things are going to be tougher.

 

[jayazusa]

Thanks for posting this it’s great info I am on my third EV and still learning. I would love to see the numbers on the Rivian’s that are out in the wild.

 

[DucRider]

Charging strategy will vary by vehicle with taper being a big part of it. The Model 3 has a big taper that starts early:

The e tron looks much different and unplugging early has less benefit:

We won't know what the optimal strategy for the Rivian will be for long distance travel. Certainly at the beginning it will be influenced much more by CCS location - not saying that you will be always be stopping at every DCFC on your route, but that will be the case much more often than with the Tesla Supercharger network (at least for the near future).

 

[ajdelange]

As it turns out if you do calculations of charging times using various taper breaks and slopes taper characteristics don't have that big an effect. Taper does have an effect, of course, it's just that it isn't as big as some seem to think. In addition to that the car changes it taper profile according to a whole host of factors. As you don't know what the taper profile used in a given charge is until after the charge is over you can't really use taper to estimate charging time. A more reasonable approach is to try to figure out what the OEM is trying to achieve. We know that in general that means an average C of 1 with higher rate being allowed at lower SoC (this is where taper come from: as the battery fills the car lowers C). But again, as the algorithms used by BMS are so sophisticated we can't expect to get much insight as to how the manufacturer strives to reach his goal but we can get a rough idea as to what result he gets. It seems that Tesla's charge at SuperChargers at a rate of about 0.9C. This implies a charge from 0 to full in 1/0.9 = 1.11 hr. This implies that one could charge from 20% to 70% in about 33 minutes and indeed this is what my personal experience has been with the Tesla SC network. The charging strategy undertaken by a Tesla driver depends on knowing that he'll charge at about 0.9C and the Wh/mi he thinks he'll use.

Now how about Rivian? Well, we don't know, of course, except to make the assumption that while they may not have the experience Tesla does they have smart folks quite capable of learning from what Tesla has done and poaching their engineers. Will they "beat" Tesla at charging by allowing their cars to take C or 1.2C? If they want to but of course that comes with some risk i.e. shorter battery life and I expect that they have a pretty good expectation as to what is involved there. So I'm guessing that they probably won't allow charging at more than about the same 0.9C. This means a full charge in 1.11 hrs or that the 400 mile version could add about 222 miles in half an hour. Thus I don't expect my charging strategy to be much different in the Rivian from what it is in the Tesla except, of course, that half a tank in 200 miles in the former and 170 in the latter. But maybe I'll be surprised. In any event I think that this video should be very informative to prospective Rivian drivers.

Note:Tesla seems to allow charging at around 1C but they are quite clear in their instructions that you shouldn't charge at that rate unless you have to. It is preferable to charge at home at closer to 0.1C. It will be interesting to see if Rivian's manual has that same caveat.

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