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Cold Weather: Don't Ignore the Warnings

Took a trip from SF to Tahoe this weekend, with a stop at the Folsom supercharger in each direction. Although it was definitely a learning experience, the lessons mainly reinforced things I've heard said again and again about EVs... but which hadn't really sunk in without experiencing them.

1) If the temperatures are low, you really, really must plug in. -- During the first night that we were there, the temperatures sunk to -8F (negative eight), and the battery lost 30 (thirty) miles of range overnight while keeping itself warm. Every time you put the car in park while in cold weather, the car warns you and suggests that you plug in... Don't Ignore this Warning.

2) Climate control and primarily-uphill driving can cause the battery range to be severely over-reported. -- The drive from Folsom to Tahoe gains 6000 ft of elevation: in order to drive the 100 mile distance, we used 190 miles of charge, meaning that we arrived with about 80 miles to spare. I had originally been planning to not charge in Tahoe at all, but due to point (1), it became absolutely necessary.

3) The superchargers are freakin' awesome... but they are not an alternative to charging overnight at your destination.

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Despite the slightly hair-raising Saturday morning with only 50 miles of range left and the corresponding hasty plugin to a 120V outlet, the trip was a success. Before attempting the trip again though, let's all let the Tahoe resorts know that we would be more likely to patronize establishments that provide charging!

To your point 1, there was a thread here that posted a Tesla response to that question stating that you don't really lose that much range, it is a software glitch that calculates the range wrong because cold li-ion battery releases energy slower. It's all there, but you don't get it out before battery has heated up.

-22C is a bit too cold for batteries without heating though, so it might be that it did need to use a bit energy to keep it warm, so truth is somewhere between "not lost much anything" and "lost 30 miles".

(Assuming 400Wh/mile, 30 miles would be 12000Wh, 8 hours for overnight, 1.5kW of power seems quite a lot for just maintaining battery temperature. If that is true, Tesla should think about increasing heat insulation in the battery for next version of the system)

Timo;
Removable heat insulation that doesn't cook them in the summer and/or hotter climates?

With liquid cooling it works both ways, it doesn't let heat in in hot climates, or heat out in cold.

Insulation is not active cooling; quite the reverse. The problem in summer is adequate heat removal, not blocking heat penetration. The batteries make more than enough of their own.

Yes, but with liquid cooling you can use radiators to remove the heat, so it doesn't matter much if you can't remove it thru battery pack wall.

I think considering where majority of the target customer base lives excess cold (in case of battery, not people) is bigger problem than heat.

Also removing heat is more energy efficient than heating in Model S (heat pump AC AFAIK).

I'm sure it seems that way in Finland. But there are more overheated than overchilled cars. And heat does far more damage, especially permanent damage. Both types must be dealt with, of course.

I'm with Timo on this one. With active cooling / heating, the battery pack does not depend on heat dissipation through the battery pack wall.

Imagine yourself in an air conditioned house in the hot dessert summer. You want good insulation to keep the heat out, not open the windows to "let the heat out" (how can you? it's hotter outside!).

Pretty simple-minded of the TM engineers to have not thought of a nice protective and insulating layer of plastic under the battery then! Send them an email suggesting it.

I'm sure they could use the laugh.

@Brian H, don't be so patronizing, you have pointed out quite a few NNIC -issues in the car yourself, this might well be one of those cases.

If it was removable, for seasonal use, there might be some use for it.

Why removable? I think permanent insulation is the way to go. Keep the cold away from the batteries.

As long as the batteries already are liquid cooled all one need to get rid of even more heat is a radiator. As we have seen on turbo cars with intercoolers there is really good effect in radiators. So even if the battery bottoms was heavily insulated heat would escape true radiators. Even when not driven a water pump and a fan forcing air thru the radiators would remove excessive heat without draining much power.

It's probable that convection heat loss through the bottom of the battery pack is part of the overall cooling system design, and that minimizes the size and weight of the radiator system. Kind of like a big radiator by itself. In any event the cooling fluid must be hotter than the outside air for cooling to occur, and in order to minimize that difference you need as much surface area as possible.

I'm just guessin'!

GAS;
prezackly.

The battery pack is big, and flat. High ratio of surface area to volume. It is not going to be easily insulated with a big, flat piece of plastic... that's why thermos bottles are round. Also it is ALUMINUM which is the best heat conductor after gold, silver, and copper- so any residual heat in the battery will conduct away to the body of the car by conduction. That can't be isolated, since the battery pack is also part of the structure of the car.

So, physics is not on the side of this idea.

DTsea;
Oil keerrect, except to note that the battery is sheathed in steel (for structural reasons).

Pretty much any metal is great heat conductor, steel doesn't fall far behind aluminum in that.

Pretty much just for that reason even small insulation between battery and that steel frame would make quite a big difference in heat insulation. Of course you would then need a bit bigger radiator to cool it down, but I don't think that would add significant amount to car total mass.


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