Range - Temperature

[heikospallek]

So, now that it gets colder in Pittsburgh, I checked my range again. I drive in E mode each morning 23 miles from home to work where I have a parking spot with free charging (Level 2) :

Date: 10/7
47 miles range indicated at home -> 23 miles drive -> arrived at work with 21 miles range indicated at an outside temperature of 54F

All entries below follow the same pattern, always 23 miles drive:

10/15
70 -> 49 @ 64F

10/16
35 -> 16 @ 52F

11/07:
29 -> 7 @42F

11/19:
29 -> 1 @11F (that one was a bit scary)

CU
Heiko

 

[Ferdball]

11/19:
29 -> 1 @11F (that one was a bit scary)

Wow! Temperature has a huge factor. So you're saying that at 11F, you only get a range of 29 with a full charge, and only about 24 actual miles?

 

[heikospallek]

29 -> 1 @11F (that one was a bit scary)
[/quote]
Wow! Temperature has a huge factor. So you're saying that at 11F, you only get a range of 29 with a full charge, and only about 24 actual miles?[/quote]

No, I had it charged up to 29 miles (I always charge at my workplace instead of at home), but I could barely finish the 23 mile ride on the 29 miles projected range.

 

[sendler2112]

Can't you charge it up better? Constantly running around using the last 10% of the battery is bad for it.

 

[heikospallek]

Can't you charge it up better? Constantly running around using the last 10% of the battery is bad for it.

I assume these are high-end lithium batteries without memory effect or any other adverse effect regarding charging behavior except overheating them. Am I wrong?

 

[sendler2112]

With Lithium batteries, the further you stay away from the extreme end of the charge or discharge cycle the better. At either end you are yanking the ions out from one side of the electrode where they have been stuck and are the last ones to leave, and jamming them across into the other electrode where all the good spots are already taken, into spots where they don't really fit as well. This is cycle wear which is greatly accelerated at the extremes. The charge end of the cycle is well controlled by the BMS. The other thing that happens at the extreme discharge end is that the individual cell or parallel group that is already the weakest, suffers the most. The discharge end is controlled also but why push it if you are only really needing 20-40 miles regularly?

 

[heikospallek]

With Lithium batteries, the further you stay away from the extreme end of the charge or discharge cycle the better. At either end you are yanking the ions out from one side of the electrode where they have been stuck and are the last ones to leave, and jamming them across into the other electrode where all the good spots are already taken, into spots where they don't really fit as well. This is cycle wear which is greatly accelerated at the extremes. The charge end of the cycle is well controlled by the BMS. The other thing that happens at the extreme discharge end is that the individual cell or parallel group that is already the weakest, suffers the most. The discharge end is controlled also but why push it if you are only really needing 20-40 miles regularly?

Thanks for the explanation! That helped.

CU
Heiko

 

[erix]

With Lithium batteries, the further you stay away from the extreme end of the charge or discharge cycle the better. At either end you are yanking the ions out from one side of the electrode where they have been stuck and are the last ones to leave, and jamming them across into the other electrode where all the good spots are already taken, into spots where they don't really fit as well. This is cycle wear which is greatly accelerated at the extremes. The charge end of the cycle is well controlled by the BMS. The other thing that happens at the extreme discharge end is that the individual cell or parallel group that is already the weakest, suffers the most. The discharge end is controlled also but why push it if you are only really needing 20-40 miles regularly?

sendler2112, this is all correct, however we do not know what level of actual battery charge is left when the car is at zero indicated range. From what I understand it is nowhere near 0. I would assume that this residual charge at zero indicated range is designed with safety measures that rule out the effects that you describe.

 

[sendler2112]

safety measures that rule out the effects that you describe.

I wouldn't say rule out. I might hope for minimize. 0% on the dash might really mean 10% in the battery. 60%-40%-60% is the ideal range if you are only using 20 miles.

 

[TonyWilliams]

It's only a matter of time before we know the exact battery specs, but here's the "sister" Tesla powered Toyota RAV4 EV.

45-48kWh total (36kWh Mercedes)
41.8kWh usable (31.5 or 33)

4.15 max cell resting voltage (same)
92 in series (92 or 96 likely)

382 volt pack max @ 4.15v (382 to 400)

386 volt pack maximum during regen (4.2 volt highest cell voltage)


2.5 volt minimum cell - cutoff / contactor open (2.5 to 2.8v)

Panasonic 18650 cells, 2900ma (probably 3100 to 3400ma)

 

[sendler2112]

Some info on the B Class electric battery as stated in my online MB tech training.
.
.

.
.

 

[TonyWilliams]

It's going to be the same basic configuration as the RAV4.

92 cells in series * 4 volts = 368 volts (28kWh usable)

It's also going to be 2900ma cells.

 

[mddg]

That is good information about the sister EV. I will add that in the recent cold snap from the "Polar Vortex" today in the DC area, I found a 65% drop in the battery over 45 miles. Temperatures hovered around freezing (28-35 F). That should amount to a total range of 45 miles/65% * 100% = 69 miles. That's driving somewhat aggressively (less conservative) with the climate control on.

I ignore the range indicator because I think it doesn't give me anything useful. The battery percentage seems to be more reliable. Still I have noticed that the 100% drops to 99% almost immediately. I think that's because rounding is by truncation here, so 99.9% gets rounded down to 99% depending on the internal precision. That makes range estimates based on the percentage a little trickier, but it won't be too important with long drives anyway.

It looks like the range indicator may be updated in the 2015 model based on the 200 km ranges shown on the dashboard displays in the newer reviews. It's possible that the range on the 2014 is based on the wall efficiency also displayed, and that's probably a mistake that gives lower range estimates. I would expect a future firmware update to fix all this.

 

[heikospallek]

I am still puzzled that some people talk about 80 miles range (without range extender) and I have never seen more than 67 miles in E mode.

 

[sendler2112]

It's going to be the same basic configuration as the RAV4.
92 cells in series * 4 volts = 368 volts (28kWh usable)
It's also going to be 2900ma cells.

So if my info is correct regarding the 3696 number of cells, even at a conservative 4.0v charge cut off, and 2900 mAh, the MB battery multiplies out to 42.873 kWh. Exactly the same as the Toyota? At the 28 kWh cut off of the MB this is a very conservative 65%. Knowing this, it seems that regular use of the extended range charge button would do no harm to the cycle life of the battery. Now I am anxious to get our car in stock from the port so I can play with the StarDiagnosisSystem machine to get some actual values.
.
Our first car hit port 15 days ago but we still didn't get it. It seems that it should have been here by now.

 

[sendler2112]

Charge/ discharge graphs for the Panasonic NCR18650 cells reportedly used by Tesla in the MB electric B Class battery.
.
.

.
.

.
.

.
.

.
.
.
.
.
.
.

 

[sendler2112]

Compare to a curve of an 8s 100Ah GBS LiFePO4 battery. The Panasonics seem as though they are not yet struggling even at the recommended charge cut off of 4.2v. Whereas there is no sense in pushing the Fe chemistry of the GBS beyond 3.4v per cell even though they are usually balanced at 3.6v or higher. You are just torturing the cell with no real added power staying in.
.
.

.
.

.
.

 

[sendler2112]

If you stay between 3.6v and 4.05 you can get 3000 cycles to 80% of original capacity. That will be a pack voltage of 370v (just above the normal charge cut off) to 330v. Maybe when I get our car I can log some actual values while I'm driving the range test to see where these numbers fall on the "fuel" gauge and percent read out. It looks from the factory cell curves that this might be around 100% to 50%.
.
http://www.teslamotorsclub.com/showthread.php/12709-18650-Batteries/page6?p=340581&viewfull=1#post340581
.
The chart from Mercedes at the top of the page shows the normal minimum voltage to be 2.74v. Don't run your battery to the bottom if you don't have to.

 

[TonyWilliams]

It's going to be the same basic configuration as the RAV4.
92 cells in series * 4 volts = 368 volts (28kWh usable)
It's also going to be 2900ma cells.

So if my info is correct regarding the 3696 number of cells, even at a conservative 4.0v charge cut off, and 2900 mAh, the MB battery multiplies out to 42.873 kWh. Exactly the same as the Toyota? At the 28 kWh cut off of the MB this is a very conservative 65%.

You are not using the nominal voltage. The pack is 36kWh.

When fully charged, Tesla will allow 4.15v resting per cell. 4.2v is reserved for charging / regen.

Probably 31-33kWh usable.

 

[sendler2112]

I see what I did wrong. I used the 4v charge cut off voltage of the MB as the voltage figure when I figured the power when I should have used the average voltage over the cycle which will be about 3.5v.
3.5v times 2900ma times 3696 cells = 37.514 kWh.