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Wh/Mile -- Difference between 60kWh and 85kWh batteries

I know there aren't many 60kWhs on the road yet, but I am curious as to what Wh/mile they are getting.

Looking at past threads on the 85kWh battery from Rod/Barbara and others, it appears the EPA rating comes out to approximately 307 wh/mile (this comes from assuming 95% of the battery pack is available for use, which leaves 80.75kWh. If you divide this by 265, you get 305 wh/mile - very similar to 307 wh/mile estimated by Rob/Barbara).

However, when you do the same type of math on the 60kWh battery, you get a much lower Wh/mile average for the EPA rated range. For example, if you again assume that 95% of the battery is available for use, that leaves 57kWh. If you then divide this by the EPA rating of 208, you get 274 wh/mile. This is significantly lower than the 305-307 you get for the 85kWh battery.

Does this inherently mean the 60kWh battery uses about 10% less energy to operate (on average)? Is this due to the fact that horsepower/torque is lower? Can we expect the 40kWh to use even less energy, average?

Any insights would be greatly appreciated.

I have a 60kWh car but it's so new that I am having problems keeping my consumption below 400 wh/mile. I can verify that it's wicked fast though!

Hans - on a "normal" trip, what kind of wh/mile are you seeing? Are you in cold or temperate climate?

I'm not sure what a "normal" trip is but I would be happy to drive a set speed on cruise control for a set distance and let you know what the avg consumption is over that distance and terrain. I am in the San Francisco Bay area so a temperate climate. My avg consumption over the last 300 miles is 370 kW/mile but that is definitely NOT normal driving for most people.

Any info would be great. It doesn't have to be cruise control but just standard driving that doesn't include gunning it at every opportunity. Although that is obviously the most fun thing to do.

Just pick an ordinary, old-fashioned car, and pace it. ;p

I have started capturing w/mile
https://docs.google.com/spreadsheet/viewform?om=true&richtext=false&form...

Results can be seen at
https://docs.google.com/spreadsheet/lv?key=0AhXq4QSAykf4dHc3Y2JwSmlpMWdF...

All entries are currently from 85s with avg of 329 w/mile

Response to shoendp. Reasonable estimate for Li-ion battery energy density is 150 Wh/Kg. so that means then the 85 kwh battery will weigh about 570 kg. The 60 kwh battery would weigh 402 Kg. so the weight difference is about 167 Kg (367 lbs). I am not sure the Wh/mile numbers you estimate can be explained by just the weight difference. So my gut tells me it has more to do with driving style than battery type.

Plus, not only does the 60kwh have less weight, it also has less battery to regulate the temperature of, which reduces electricity usage.

@crttnarayan/@archibaldcrane - have you seen any info from TM about this that supports the idea that the 60kWh car is lighter? All the informal info I've heard from TM and seen on the forum says that the 85 and 60 batteries are different chemistries, have different energy densities, and approx the same number of cells, hence the same weight.

The Model S specs page only shows one curb weight, not different weights for different models.

I talked to the Tesla Ownership team today and they said that Tesla is now publicly stating that the 60kWh version is lighter than the 85kWh version. However, they still will not give specific weights. They also said that the configuration of the 40kWh was not complete yet, but that it would be lighter than the 60kWh. I did not write down the name of the guy I talked with, but he seemed very confident in the weights and did not waffle at all when I questioned him.

@crttnarayan, Tesla is using Panasonic NCR18650a for 85kWh Model S, about 8000 of those gives you 90kWh. Each cell weights 46g. That gives batteries alone 368kg. Energy density for those batteries is about 243Wh/kg, so you are off by about 90Wh.

Battery casing doesn't change between models, but wiring does. I have no idea how much that adds / cell, and also how they change the cooling for different models is unknown, but anyway, weight difference should not be as big as you estimate it to be.

@schoendp, 40kWh have to be quite a lot lighter because 160/300 > 40/85 and only thing explaining that increase in range/kWh for 40kWh model is that weight difference.

Same actually applies to 60 and 85 too: 230/300~=0.77, 60/85=0.70.

@Timo, while the energy density of the cell is close to 250 Wh/Kg the energy density of the battery pack is substantially lower because of how the cells are independentally housed. The 8000 cells are grouped into small number of cells which are clustered into battery packs. Several of the battery packs are packed into the battery housing. While the battery housing or casing is nominally the same for all the models what is different is the number of battery packs they have for the different models. These battery packs have energy densities closer to 150 Wh/Kg. For crash test safety reasons the housing is the same and the packs are distributed so the weight distribution is uniform. There will be small differences in housing to permit even distribution of battery packs, which is why you cannot upgrade the battery after you buy the car. This was how it was explained to me when I took a detailed tour of their R&D test floor in their Palo Alto lab.

The biggest difference I've experienced so far (I don't drive long distances) is the $10k. Glad I got the 60.

I have a hard time believing that those "packs" would be so drastically heavier than cells in them.

I would estimate closer to 200Wh/kg / "pack" ("cluster" might be better word). Or did they say to you that each cluster has 150Wh/kg energy density? Was that with or without cooling? Because I believe that plays quite a big role in the final weight of the entire pack (water is heavy), and I have no idea how that is made, does is follow the same ratio as cell number in the pack?

Take a look at some of the pictures posted on the MyNissan Leaf of the internals of a Tesla battery pack:
http://www.mynissanleaf.com/viewtopic.php?f=10&t=2429&start=1080#p261871

@murraypetera - sorry, the 3235 entries in your spreadsheet should be 85kWh + air + 19" wheels

Has anyone done LA to SF in the 60? How does it measure up on the highway between supercharging stations? I was told by a tesla rep that it would make it - but that I may have to drive 55mph. Any advice would be appreciated, we are tethering between the 85 and 60

@asadkhaha
I drove from Fremont down to LA with two stops. Not sure where in LA you are starting from. Fremont to Harris Ranch was 155 miles. I went about 65 mph and started with max range from the factory. Second stop at the grapevine and travelled about 110 miles at 70-75 mph. If you are going into the city I would consider making a third stop in Gilroy and you should have no problem. Hope that helps.

You know I kind of wish they would allow you to buy a car with the 85 pack and then choose weather you want 40 or 60 as your actually capacity that way you can upgrade it like they are doing with the 40kh/w packs

ajamison;
teetering
whether

That's not a half-bad idea. I wonder if TM will take it up.

I have a 60kWhr. Average for me is 275 W/mi on a commute to work with speeds between 40 and 60mph and many stops/starts keeping up with regular traffic. A 70 mile drive down flat I-5 at a constant 65mph is the about same.

I have a 60 kWhr. Average for me is 309 Wh/mi over the first 800 mi. This is about 60% highway and 40% local roads on mostly flat New York metro area roads.

My 60 kwh averages around 290-300 wh/mile for freeway and street driving of 30 miles round trip commute everyday.

I like the idea of upgrading batteries for travel and then get back your original one. I actually talked about THIS being the big announcement 'under the nose' elsewhere on this forum.

After looking at the battery pack, there is a lot of weight and space overhead to cool the batteries, control the current flow and fuse the batteries individually. Wondering if the fuse wires create a lot of resistance and drop voltage significantly. Over time I would expect Tesla to optimize the design and reduce weight and volume of the packaging. May be even add more cells without increasing the weight.

I drive a P85 and I'm averaging 309 Wh/m since getting the car. I have gone as low as 250 Wh/m on some trips.

@asadkhaha
I agree with mbcaffe, the LA to SF route is very doable in a 60. I live just north of LA and we have made three round trips to San Jose. we have taken the "5" and the "101" and the superchargers provide adequeate coverage. We averaged 70-80 mph with the A/C on.
And to the main point of this thread: We have had our 60kw Model S for 7 months and 13,000 miles. The average over that span is 317wh/mile.


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