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# Tesla Motors, Inc. (TSLA) Message Board

• fartman1953 fartman1953 Jan 1, 2014 8:08 PM Flag

## JOHN BRODER WAS RIGHT

In his test drive Broder got stuck because the Model S failed to perform in cold weather. Of course Elon blasted him for rigging the test drive. Flash forward to today and read the forums. With all of the cold weather owners are reporting drastic reductions in mileage capabilities. Elon needs to apologize to Broder.

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• My mileage in cold weather has actually gone WAY UP!! I find that when my model S is being towed, it uses almost no battery power. I was towed almost 150 miles a couple of days ago and mile miles/kW actually rose. So quit bashing my here!

• Consumer Reports reported the following last week: with heater on ,30 degrees, Tesla lost 3 miles per mile driven.

• Yes, cold does affect battery efficiency but not as bad as you guys claim. I know someone that has a p85 and his range in very cold weather is about 25 miles less. did you know that gasoline cars are also less efficient in cold weather? nothing new here.

• Give that tiny brain of yours something to think about:
The behavior of a typical internal combustion engine can be approximately modeled by a thermodynamic concept called the Carnot cycle.

Through a bunch of math, which I won't bother deriving, it can be shown that the maximum possible efficiency of a heat engine obeying the Carnot cycle is equal to 1-Tc/Th, where Tc is the temperature of the cold reservoir, and Th is the temperature of the hot reservoir.

A "reservoir" in a thermodynamic context is defined as being "an infinite source or sink of heat," or in other words, it's something which can absorb or give an infinite amount of heat without changing its temperature.

So, in normal operating conditions, we can effectively consider the radiator and cooling system to be the hot reservoir, and the ambient air to be the cold reservoir.

So, as you can clearly see, as the temperature of the cold reservoir decreases, and the temperature of the hot reservoir increases, the maximum efficiency increases.

So, now, let's crunch some numbers.

First of all, in order for the equation to be true, we need to use an absolute temperature scale-i.e. one which does not have negative temperature values. The most common is the Kelvin scale. Since this is the US, however, and we tend to report temperatures in Farenheit, I'll use the Rankine scale. To convert Fahrenheit temperatures to Rankine temperatures, simply add 460.

So, now, let's assume in all cases that the engine is operating at a constant temperature of 200 degrees F, or 660 R.

If the ambient temperature is 100 degrees F, or 560 R, the maximum possible efficiency is 15%.

At 50 degree F ambient temperatures, the maximum efficiency reaches 23%.

Finally, at 0 degrees ambient, the maximum efficiency reaches 30%.

So, here's my conclusion:

If and only if everything else is absolutely equal, the engine will operate more efficiently at lower ambient temperatures.

@ELECTROJERK A mind is a terrible thing to waste.

Sentiment: Strong Sell

• John Broder is lucky that he didn't get sue for faking the test he need to apologize to Elon and I believed he did already.

Sentiment: Hold

• Yep, here is the link, Why do electric cars suck in cold weather?
In hindsight, it’s not surprising the Mitsubishi MiEV EV I drove barely made it to 50 miles rather than its rated 62 miles (100 km). It was a dark and chilly if not stormy early December night and that killed the range. When you drive an EV, “your mileage may vary” includes cold weather as well as hard acceleration and late braking. As temperatures dip below freezing, you could lose 25% of your electric vehicle’s precious range. Batteries are less efficient in cold weather, they don’t regenerate as well, and electric heating for the cabin, seats, and windows drains your range, too.

The same thing happened when I drove a Tesla Model S. With the 85 kWh battery, the Tesla is good for around 250 miles. During the afternoon with temperatures above freezing, the discharge rate indicated I wasn’t far off from that kind of efficiency. Driving at night as temperatures fell into the 20s (0C to -5C), I found the range fell noticeably faster than the distance gauge suggested at the start of the trip.

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