Range - Temperature

[heikospallek]

Here is another possibility to consider with the sub 0C overnight temps. You are only charging at work so the car is not plugged in overnight. I wonder what and when the battery heater is doing. See if you can take note of the battery percentage toward the end of the trip home when everything is warmed up and before you get out when you park the car. Versus what it says in the morning before you take off and during the first part of the trip before everything is warmed up.

I have watched this--but for another reason. I use the remote climate control and it uses up "1 mile" to heat up the car, but I am conscientious about what it says when I park and what it says when I leave the house. I was initially afraid that this will use a ton, but it does not.

<<You could even reset the trip computer a few times each way to get an idea of the average consumption at different stages of the round trip. Set up a video camera of the dash so we can see what it says and when while you are driving?>>
Good idea. I will do that after the long Thanksgiving weekend and post here.

CU
Heiko

 

[sendler2112]

So the battery is 100% healthy. And you are driving carefully. Three 23 mile trips per full charge. You are coming up 3kWh per trip short of the 90 mile range that others are regularly getting. Each cold start and climate control use during the trip on 20F days could account for that much between the battery heater and the cabin heater. Everything in the car and in the battery system is just getting nice and warm right about the time you park it. Where it sits and gets cold again until the next cold start.
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A continuous range test on a 70F day doesn't have any of these losses.

 

[heikospallek]

Set up a video camera of the dash so we can see what it says and when while you are driving?

OK, I did this for my trip from work (fully charged) to home (no charging at home) and then next day back to work.
Check out this 5 min video (12 times faster then normal as it was shot with 2 frames per second, but plays here with 24 frames per second):
http://vimeo.com/113661901

 

[sendler2112]

Now that you have watched the video yourself, what do you think? I see a couple things. The most obvious is when you parked the car at the end of the first trip the GOM said 40mi. When you started the car for the second trip after it sat, the GOM siad 34mi and quickly went right to 33. So it looks like you are losing 6 miles from the various preheating processes or after run processes during the time it is parked. Something similar is happening at the beginning of the first trip where your average consumption dips down to 1.5 mpkWh. Even though the cabin was probably pre warmed while the car was plugged in, it seems there is a lot of energy being used that is not making motion. Plus it does look like that leg of your commute is forcing you to hammer on and off the gas and brake quite a bit. Interesting that while you are driving your GuessOMeter is dead on. All of this looks normal I'm afraid. When it is cold out you are only going to get 60 miles and it could get much worse in sub 0F weather.

 

[heikospallek]

Now that you have watched the video yourself, what do you think? I see a couple things. The most obvious is when you parked the car at the end of the first trip the GOM said 40mi. When you started the car for the second trip after it sat, the GOM siad 34mi and quickly went right to 33. So it looks like you are losing 6 miles from the various preheating processes or after run processes during the time it is parked. Something similar is happening at the beginning of the first trip where your average consumption dips down to 1.5 mpkWh. Even though the cabin was probably pre warmed while the car was plugged in, it seems there is a lot of energy being used that is not making motion. Plus it does look like that leg of your commute is forcing you to hammer on and off the gas and brake quite a bit. Interesting that while you are driving your GuessOMeter is dead on. All of this looks normal I'm afraid. When it is cold out you are only going to get 60 miles and it could get much worse in sub 0F weather.

Thanks for your comments! Two notes: Yes, it is hilly in Pittsburgh so I have to accelerate and decelerate quite a bit. Second, apologies, I was cheating: I recorded the trip back and then the trip to work. As it is each day the same trip it does not make a difference regarding the actual driving, but you caught me by noticing the 6 mi difference between parking and starting the second leg. It is still not satisfying that I have only 60 mi given that it was not even that cold--considering Pittsburgh. In other words, it is a 60 mi range car in the north and an 80 mi car in the south. Maybe MB needs to put a disclaimer on it.

 

[sendler2112]

it is a 60 mi range car in the north and an 80 mi car in the south.

Unfortunately manufacturers only quote national test data so this is all an early adopter has to go on until a sizable sample of users start logging their real world energy efficiency. Which there is no log section here as there is at Ecomodders. Hopefully Fuelly will add these cars soon.
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Luckily, you really only need 46 miles of range to make a round trip. Can you plug in to normal 120v at home or are you in an apartment? Even at the low setting of 8 amps you could add 10 kWh overnight which would cover the 3kWh warm up processes and add miles giving you back an additional 20 miles. And be much kinder to the battery, keeping it warm overnight instead of waking up harshly in the morning at brutal overnight low temps. Any normal 50 foot extension cord could handle this.
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We didn't get to see the Ecell gauge in the video. Does the needle dip at all when you first start out after sitting all night, dead cold? It would be nice to see the whole instrument cluster somehow so we could see the speedo also. Maybe hang the camera from your neck or clip it on the seat belt.

 

[heikospallek]

Luckily, you really only need 46 miles of range to make a round trip.

Yes, and as you correctly pointed out, I can plug in at hoe as well. No problem.

We didn't get to see the Ecell gauge in the video.

Forgive my ignorance, which display/screen is this? Take a picture for me and I can shoot another video with the display on all the time.

 

[sendler2112]

The Ecell gauge is the small, round gauge on the right, inside the large round power gauge. It will normally be straight up at 100% and shows how much of the maximum power is available. If the battery or drive were to get too hot while climbing a mountain in hot weather, the E-cell gauge would dip down to alert you that if you floor it, the acceleration will be limited and won't take off as quickly as you may be used to. I wonder if starting off in the morning with a cold 20F battery might call for some limiting also which would be an indication of how tough cold temps are for the system to take. I know from my research of other types of batteries such as the LiFe GBS cells that permanent plating will occur if they are hit with a high charge current when they are below 20F. They will permanently lose 20% of their capacity overnight. I assume the bms and the battery heater would be used to prevent this in any consumer application such as a car.
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Running the 120v charger on low at home will only cost you $1.50 and would certainly help extend the life cycles of the battery when low winter temps are forecast.

 

[heikospallek]

The Ecell gauge is the small, round gauge on the right, inside the large round power gauge.

It seems to be all the time 100% (full).

Also, did you read:
http://bmwi3.blogspot.com/2014/12/bmw-i3-psa-no-there-is-nothing-wrong_8.html?m=1
?

 

[sendler2112]

Also, did you read:
http://bmwi3.blogspot.com/2014/12/bmw-i3-psa-no-there-is-nothing-wrong_8.html?m=1
?

Good find. This is just what we have been talking about.

 

[TonyWilliams]

Also, did you read:
http://bmwi3.blogspot.com/2014/12/bmw-i3-psa-no-there-is-nothing-wrong_8.html?m=1
?

Good find. This is just what we have been talking about.

I use a simple rule of thumb on lithium cells that we lose 1% capacity per 2C/4F below 20C/70F, therefore a freezing temperature of 0C/30F would lose 10%, and a really cold temperature of -20C/-10F would lose 20%. Again, I'm talking about BATTERY temperature, not ambient air temperature.

This works great until you start to factor in the power consumption of the battery heater, which is going to be vastly different for every car and situation. The ONLY way to know how much power that is would be to read it off the CAN bus on the car, or measure it with your own equipment. There are just too many variables to accurately guess. The same goes for cabin heating.

So, let's say that you're the advanced EV driver, and you know that to get maximum range, you needed to preheat the cabin and battery (and you've done that), and by some stroke of luck, the battery just happens to get over 20C/70F.

So, we are starting out with ALL the available energy that the battery has to offer. If you have a heated garage, this might actually be the case. So, the other variables to range (not what the GOM says, but actual range... how far can the car go given a set of metrics) can be estimated.

We now know that the Mercedes B-Class ED can go:

100 miles "normal" charge (28kWh)
113 miles "extended" charge (31.5kWh)

Given dry level hard surfaced roads with no wind and a steady 65mph, and no heater use with a 20C/70F battery temperature, which will consume 3.6 miles per kWh. Sadly, you'll need to multiply your dash display's energy consumption data by 1.2 to get an accurate consumption rate.

The other factors are:

Speed - thankfully, this is very easy to calculate.
Wind - easy to factor
Snow, Rain - you're going to have to guess
Cabin/Battery heater - another big guess
Ambient Temp - easy to factor increased air density in cold air
Winter tires - you may have snow tires that increase rolling resistance

That's really it. The bottom line is to know how much energy you start with and monitor the consumption to make sure that you're going to make it. With experience, you'll learn that the worst combination of events can cut your range in half.

 

[TonyWilliams]

Longest Range Pointers


1) Drag - Wind resistance - high elevation and hot ambient temperatures thin the air, making it easier for any object to pass through the air. In the airplane business, we call this calculation "density altitude". Here's an easy to use online version: http://wahiduddin.net/calc/calc_da.htm. The most "aerodynamic" vehicle will cut through the air with the least resistance.

2) Drag - Rolling resistance - drag from everything that rotates to move the car; tires, wheel bearings, u-joints or cv-joints, gears and bearings, gear lubricant. Generally, the hotter the lubricant, the lower its resistance; the higher the tire air pressure, the lower the tire resistance.

3) Gravity and Mass equals Weight - as long as there is gravity, it will take energy to accelerate mass and energy to propel mass at speed. Obviously, it also takes significantly more power to lift the mass away from the gravitational pull while driving uphill. Quite simply, lighter is better.

4) Ideal speed - every vehicle has a speed where the intersection of the power required to overcome drag and weight is the least. Heavy cars with high drag tires (but extremely aerodynamic) like a Tesla tend to be most ideal in the 20-25mph range and small, lower mass cars like LEAF and Spark EV are probably in the 10-15mph range. Obviously, anything that uses power that isn't being used to overcome drag and weight is a waste; the heater, a/c, etc.

5) Hot batteries store more energy - the hotter the better, however, this same heat tends to significantly shorten their life (Nissan LEAF in Phoenix) and in some cases (Boeing 787), make the battery fail.

That's it! Hit the ideal speed, at the lowest weight with the least drag and the most stored energy!!!!