Large Drop in Charge When Parked in the Cold

[jkirkebo]

Don't take this the wrong way, because I'm all pro-Tesla and can't wait to get my Model S! --> but isn't this similar to what happens with the Chevy Volt during winter? Isn't there a significant drop in range when its cold out? I know they started turning on the engine below 28 degrees to help warm the car up but as far as a range drop I would think this is kind of expected in both the Volt and the Model S. So basically what I'm saying is that this range drop, if it is a true range drop, is expected behavior in this cold weather. That's not going to deter me from buying the Model S in any way though as to me that's normal. /

A range drop in the cold is not a problem, that is to be expected. Winter tires, snow/ice, cold air with higher density, heating requirements etc.

But if the battery SOC continually drops in cold weather when parked and not plugged in because the car tries to keep the battery temperature up continously, that is a problem. We do however not yet if this is happening.

If I can park my car with 60% SOC for 5 days in 0F weather, then fire up the generator for an hour before leaving to heat up the cabin and battery, and then have say 55% SOC remaining, that is fine. If I instead have 10% SOC remaining that is no good since I then have to charge for 8 hours on generator and my wife will be pissed at me:crying:

We will find out as soon as the app is released and someone parks their car in the cold for a few days without plugging in. Heating the battery & cabin from the grid should restore any SOC points missing from a cold battery.

 

[tezco]

Same problem with the Leaf. When it's below 20 F the heater draws up to 4500 W which is more than the engine is pulling on level ground. Typically I live with a little less comfort and get a third less range. The "calculated" projected range is more like what you expect at 45 F, and the figure isn't reduced as the heater draw increases at low temp. I don't think the LiIon battery output really falls off that badly in the cold, but whatever it is just adds a little more insult to what the heater use causes. I suspect Nissan didn't tie the actual heater draw into the calculation of projected range since otherwise "range" would plummet when the heater first came on (since it runs full blast for a while). I don't know how the S calculates the projected remaining range, but it is less variable than the Leaf's , which bounces all over the place (the Leaf's seems to mostly be based on your last couple minutes of engine current draw).

 

[JRP3]

This is about the loss of charge while the car is parked, not reduced range from driving conditions. There is a difference as jkirkebo describes.

 

[MikeK]

Howdy!

I'm back from a weeklong trip, during which my Model S sat unplugged. It was parked in the San Mateo area, in a parking garage that is at roughly the ambient outdoor temperature. I believe the high temps during the past week were in the 50's and the lows were in the mid-40's, but somebody who was actually here can probably give better figures.

In any event, I parked the car last Saturday morning with between 220 and 230 miles of range showing. I'm sorry I neglected to write down an actual figure, but it had been on a standard charge overnight and then I drove 4.4 miles on city streets to my friends' place to leave the car in their protected garage.

Upon my return this evening (Saturday, so 7.5 days later), the car was showing 191 miles of range available. The handles extended when I walked up, and everything worked normally. The regen was limited to a bit over 15kWh and that limit climbed to about 30kWh by the time I got home. It's the same 4.4 miles, but with a hill climb at the end, and I had the heat on. The car was showing 180 miles of range available when I shut it down.

So, I don't think it was as cold during my trip as it was the one night that I saw the large range drop in near-freezing temperatures. But, I wanted to share this experience of a prolonged stay unplugged in chilly weather. The loss of indicated range is more than is called for in the manual (which says that the car should lose 1% per day, which would have been about 20 miles lost). I may have lost as much as twice that, but it was not drastic and I will look forward to hearing others' reports of how the car behaves in differing conditions.

 

[nolngrgrsngslde]

I don't guess the S comes with a cover. If you did cover it though when parked outside, that should reduce battery drop by keeping the heat in the battery longer.

Should I order one, guys?
http://shop.teslamotors.com/collections/model-s-functional/products/model-s-outdoor-car-cover

The Tesla S cover looks good but it should have a skirt all the way to the ground to keep cold air away from bottom of the car. Also, the front wheel is open, that let's air through as well.

 

[jerry33]

If you did cover it though when parked outside, that should reduce battery drop by keeping the heat in the battery longer.

I doubt the cover will do much for keeping the battery warm--even if it went all the way to the ground. I'll likely get one as mine will be parked outside. Whether I will use it after the first couple of weeks is the big question

 

[JRP3]

That cover won't help one bit. You'd need something heavier with at least an inch of insulation and completely covering all openings, as well as touching the ground, and even then it would have a limited effect.

 

[stevezzzz]

I don't guess the S comes with a cover. If you did cover it though when parked outside, that should reduce battery drop by keeping the heat in the battery longer.

Should I order one, guys?
http://shop.teslamotors.com/collections/model-s-functional/products/model-s-outdoor-car-cover

The Tesla S cover looks good but it should have a skirt all the way to the ground to keep cold air away from bottom of the car. Also, the front wheel is open, that let's air through as well.

I don't favor a car cover for the purpose you propose, for two reasons:

1. It doesn't do much to slow battery cooling since the entire bottom of the battery pack is still exposed to ambient air.
2. After you drive to the airport parking garage you'll be putting a cover on a dirty car, which won't do the finish any good.

A better plan IMHO would be to spend the same money on upgrades to covered airport parking with an EV plug-in.

Or did I misunderstand your question: are you not able to garage your S at home?

 

[nolngrgrsngslde]

On the cover question:

I thought the same as you guys. I just wanted to hear some opinions.

On a normal basis, I will garage the S. Actually, it will be very happy with my well insulated garage.

 

[bluetinc]

Hey all,

I have to say I've only made it through about 8 pages of this and I'm about to pack up and head back into the car for the next leg or my trip but I wanted to through my two cents in.

I'm running 4.0, and had a few occasions to leave the car overnight now when it is cold out (sub 35 degrees F). When coming back to the car the mileage is significantly reduced, say 48 miles down to 26 miles. After driving then for a few minutes, I've watched the mileage then climb back up the about where I expected it as the pack warms up. It seemed to me to simply be voltage sag due to temperature being displayed.

Peter

 

[MikeK]

Interesting datapoint, Peter!

Perhaps the mods might want to split the Volt discussion elsewhere?

 

[FlasherZ]

Hey all,

I have to say I've only made it through about 8 pages of this and I'm about to pack up and head back into the car for the next leg or my trip but I wanted to through my two cents in.

I'm running 4.0, and had a few occasions to leave the car overnight now when it is cold out (sub 35 degrees F). When coming back to the car the mileage is significantly reduced, say 48 miles down to 26 miles. After driving then for a few minutes, I've watched the mileage then climb back up the about where I expected it as the pack warms up. It seemed to me to simply be voltage sag due to temperature being displayed.

Peter

I think I may have seen the same thing too... there have been times when I leave the garage with 240 miles displayed and it just simply "hangs" there for a few miles as things warm up. There have been times when I have pre-heated the car, gotten in, and it shows more (say, 245 mi or 250 mi) than a "normal" charge should show.

 

[tezco]

This is about the loss of charge while the car is parked, not reduced range from driving conditions. There is a difference as jkirkebo describes.

Actually, what I really care about is loss of available energy in the cold, to which is added the insult of increased heating loads. This directly relates to true available range. The SOC may be unchanged from yesterday, but when I hop into the car when it is now 60 degrees cooler, is my "fuel" gauge still accurate?

The problem is that we are looking at a very imperfect energy gauge in the S when we look at the "range" meter. I don't know if the S energy gauge factors in battery temperature, battery age/permanent loss of capacity and whether it even keeps track of 100% of the current draw from all devices. Is some of the "lost" range recoverable when the battery heats back to normal operating temperature? How much of the "lost" range is due to a true loss of electrons from vampire loads, how much from a calculated subtraction to account for less extractable energy from a cold battery, and how much is the computer subtracting from the range for the increased heating and battery warming loads that now have become active when I ulock the door?

I think it is folly to look at a change in the range meter in any EV and assume that the difference means that xxxx coulombs have been irrevocably used.

From Battery University: "Users of electric vehicles need to understand that the driving distance specified per charge is given under normal temperature; frigid cold will sharply reduce the available mileage. Using electricity for cabin heating is not the only cause for the shorter driving distance between charging; the battery performance is reduced when cold." [Would sure like to see a graph of the S LiIon battery capacity vs temp.]

See also: How to Improve the Battery Fuel Gauge - Battery University

 

[jerry33]

From Battery University: "Users of electric vehicles need to understand that the driving distance specified per charge is given under normal temperature; frigid cold will sharply reduce the available mileage. Using electricity for cabin heating is not the only cause for the shorter driving distance between charging; the battery performance is reduced when cold." [Would sure like to see a graph of the S LiIon battery capacity vs temp.]

What that misses is the difference between batteries that are thermally managed and ones that are not. Having a thermally managed battery reduces the effects of both hot and cold weather. Also, determining the SOC of the battery is more an art form than it is a science because there are a number of variables. So even if you had a graph, it wouldn't necessarily reflect what happens in a Model S.

 

[JRP3]

I think it is folly to look at a change in the range meter in any EV and assume that the difference means that xxxx coulombs have been irrevocably used.

There are a few separate issues. If the car uses some energy while parked to manage the pack, that energy is gone. Additionally a cold pack will have a lower voltage reading, which the range gauge may interpret as reduced range even though the pack may not have lost any energy. However the lower voltage and likely higher voltage sag under load means the pack will have to use more current to produce the same power, so less actual available energy. As you drive the pack warms up some which reduces voltage sag. Then on top of that you have heating loads, plus cold air is more dense, also affecting range. Current sensors may also be affected by temperature. There is a lot going on and it's going to take a lot to get it right every time.

 

[tezco]

There is a lot going on and it's going to take a lot to get it right every time.

I agree. There are so many variables to take into consideration when you try to design a truly accurate "fuel" meter. It's even more difficult looking backwards from a change read at the "fuel" meter, and trying to figure out what has changed for a single variable.

 

[Todd Burch]

As others have said, and some of the stories here seem to imply, I do think a lot of the lost range is just virtual, and when the pack warms back up some of that indicated mileage comes back. After all, the pack doesn't need to be maintained to a very warm temperature--just enough to put it over its minimum limit.

Speaking of which, why is there a minimum limit? I can understand if conditions are really cold, but if temps are 32 deg F for example, what is the harm in just letting the battery get cold? Sure, you have very limited power when you first start up again, but the battery wouldn't really be harmed, right?

We need a technical blog post from JB to cover a lot of these issues and put customer minds at ease. What happened to the blog posts? Seems like there were tons for the Roadster and very few for the Model S.

Tesla hasn't released nearly enough technical info for the Model S--especially given that most of its customers are technical.

 

[JRP3]

Speaking of which, why is there a minimum limit? I can understand if conditions are really cold, but if temps are 32 deg F for example, what is the harm in just letting the battery get cold? Sure, you have very limited power when you first start up again, but the battery wouldn't really be harmed, right?

At freezing or below, depending on the battery chemistry, damage can occur during discharge and charge, (metallic lithium plating on the electrodes which can't be reversed). I'm sure Tesla wants some safety margin so they probably keep the pack above that.

 

[Todd Burch]

At freezing or below, depending on the battery chemistry, damage can occur during discharge and charge, (metallic lithium plating on the electrodes which can't be reversed). I'm sure Tesla wants some safety margin so they probably keep the pack above that.

Ok...so some heating would be needed to keep the battery a bit above freezing...but overall that draw should be relatively small.

 

[napabill]

Being a Northern California/Arizona person, cold temps are typically not my concern. But in the transit from Napa to Tucson, I spent the night in Tehapachi at 4,000 ft. Was 36 when I arrived and 22 when I came out of the hotel the next morning. My rated range went from 185 miles to 145 miles. Tried to find a 110v outlet to keep things warm, but no luck. Fortunately, I only had 90 miles to a Supercharger. Arrived with 54 rated showing...no problem.