FlatSix911
Porsche 918 Hybrid
Someone should start a poll on the battery options ... my bet is 40kWh and 60kWh for the Model 3.
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JRP3
Hyperactive Member
40kWh x 95% = 38 / 215 mi = 177Wh/mi. Not going to happen. Come on people, do some simple math and let's try to stick to reality.
Doing the math with 300 Wh/Mi comes up with 68 KWh battery. 280 Wh/Mi comes up with 63 KWh. Unless Tesla can pull a rabbit out of a hat and come up with a car more efficient than the BMW i3 (which is unlikely) that battery will probably be over 60 KWh.
Why unlikely? The Model ≡ has a drag coefficient 27% better, probably a smaller frontal area as well. While the probable weight difference is only around 17%.
Thank you kindly.
FlatSix911
Porsche 918 Hybrid
No more debate is needed. Musk has already stated that the base battery will be under 60kWh with 200 mile range.
SageBrush
REJECT Fascism
Here is a spreadsheet I made using the drag equation. You can grab a copy and change parameters.
68 mph (110 kph) for my presumed Model3 is 191 Wh/mile of tyre and air drag. Base electronics is another 3 Wh or so. Tack on battery to wheels and you should have a reasonable number. I'm less confident about the battery to wheels number ... but at 85% efficiency (a guess) for steady speed driving, we end up with
194/0.85 = 228 Wh/mile. A 215 mile range then requires 215*0.228 = 49 kWh of useable battery.
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Tesla has been crystal clear that the base Model 3 battery is less than 60kW and the EPA range will be at least 215. I take them at their word.
You are welcome to your own opinion.
Red Sage
The Cybernetic Samurai
Keep in mind the EPA's Watt-hours per mile notation includes presumed induction losses while charging. So, the Model S and i3 BEV are both more efficient in The Real World than their testing shows. Likely no more than 85% actual consumption on the road.
An EPA of 280 Wh per mile and 215 miles would be around 60 kWh of energy to add about 54 kWh to the battery with reasonable assumptions of charger losses and anti-bricking that would be consistent with a nominal battery size of 58-59 kWh. If you assume 270 Wh EPA per mile then maybe a nominal battery of 56. Then 260 Wh would get a nominal battery of around 54 kWh. Or something like that.
It's reasonable to see how Tesla could do 215 miles EPA with a ~55 kWh nominal pack by roughly matching the i3 city efficiency while doing much better on the highway number with better aerodynamics. It's not going to be easy because the i3 has carbon fiber panels and an aluminum frame with less than half the battery size. Still, I can imagine them doing it. Beyond that I start to get skeptical.
JRP3
Hyperactive Member
Isn't it possible to calculate a more realistic Wh/mi number based on the usable battery capacity divided by EPA range? That would exclude the charging losses and uses the EPA Range cycles as a definition for "The Real World."
stopcrazypp
Well-Known Member
Math already done before shows that Tesla doesn't have to beat the i3 to reach its range goals. The original i3 is 231Wh/mi (18.7kWh usable/81 EPA miles). The new 2017 33kWh version (27.2 kWh usable) gets 239Wh/mi (27.2kWh/114 mi).
Official: 2017 BMW i3 Gets 33 kWh Battery, Range Increases To 114 Miles
To reach 215 EPA miles of range using the same consumption as i3 requires 49.7-51.4kWh usable. Tesla has ~95% usable, so that bumps it to ~52-54kWh. My bet has been a "55kWh" battery. The way Tesla can match the i3 is by better highway efficiency (i3 depends on city efficiency to get a high combined number).
Actually Musk has said no such thing. It was reported that the VP of public relations said that during a phone call. Tesla has never elaborated.
Again, they've been crystal clear that the range will be at least 215 miles. We have one reported quote from a VP referenced in the OP, and nary a squeek since about the battery being less than 60kWh. Not saying that it won't be, I just think people overstate the certainty. I just remember some people being really pissed off about the towing capacity of the X, because one exec early on stated once it would be greater than it ended up being (they lied to us!).
SageBrush
REJECT Fascism
To recap what was clarified to me in another thread: the Range number by EPA is based on useable battery and the average of the EPA highway and city tests consumption values on the dyno. Charging is not part of the calculation*. I think the Model ☰ will have an average at least as good as the BMW i3 (albeit with the city and highway numbers reversed.)
*It is for MPGe and kWh/100miles, but not for range.
*It is for MPGe and kWh/100miles, but not for range.
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I thought Elon said in the earnings call that the M3 would have a battery smaller than 70 KWh, but it appears everyone else here remembers 60 KWh, so without going back and listening to the earnings call again, I'll accept that I misremembered.
I used the i3 because it has the best EPA rating for energy efficiency right now: 270 Wh/Mi.
0.27 KWh/Mi * 215 miles/ 95% = 61 KWh
The coefficient of drag of the Model 3 will be lower than the i3, but the car will be heavier. If they get the efficiency up to 250 Wh/Mi, that would make the battery 56 KWh by the above calculation.
I used the i3 because it has the best EPA rating for energy efficiency right now: 270 Wh/Mi.
0.27 KWh/Mi * 215 miles/ 95% = 61 KWh
The coefficient of drag of the Model 3 will be lower than the i3, but the car will be heavier. If they get the efficiency up to 250 Wh/Mi, that would make the battery 56 KWh by the above calculation.
Jeff4155
Member
Is it hard to believe that Tesla might just install a 70kw battery pack and software cap it like they are doing with the MS70/75? this way they can either keep the cap on as if its a 60kw battery for the entry level vehicle or charge a few grand more to make it a 70 or 75kw model? that way they keep cost down by manufacturing one type of battery across the range?
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stopcrazypp
Well-Known Member
I guess I should clarify, since I see your confusion. The 270Wh/mi EPA sticker number can't be used with the EPA range to get usable capacity. That EPA efficiency number presents the EVSE to wheels efficiency (including charging losses).
As an example, the 90D gets 33kWh/100mi (EPA) and 294 miles of range. 33kWh/100mi * 294mi = 97 kWh, which obviously is not the usable capacity (or even the nominal capacity), but rather the charging consumption (AC kWh).
2016 Tesla Model S AWD - 90D
For the 2016 i3:
270Wh/mi * 81 mi = 21.95 kWh, however usable capacity is only 18.7kWh. That 21.95kWh represents how much AC kWh is necessary to charge the car (not the DC kWh required in the battery).
2016 BMW i3 BEV
You may have been confused because the AC kWh charging number for the i3 happens to match the 22kWh nominal DC capacity. Tesla example is more clear (you can also try with other EVs like the Leaf).
As such, the usable battery capacity (DC kWh) must be used to figure out the battery to wheel efficiency, as I did in my post. This comes out to 231Wh/mi for the older version of the i3 (not the 270Wh/mi figure). The other math follows from there.
Tesla confirms Model 3 will have less than 60kWh battery option
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That's an intriguing thought. We're so used to thinking of the S pack containing dummy cells and that it's only a higher optioned vehicle which can mimic the performance of less capable Model S's.
If all versions of the Model 3 are fitted with the same pack then it could extend the Auto Pilot trial idea. You could have the option of living with a larger battery/longer range for a period of, say, a month. The full range of performance would probably not be available, since that needs more than just a larger capacity battery. But I imagine that under 6 seconds 0-60 could be swapped for an under 5 trial quite easily.
Maybe the trial could be non-continuous - your month could be two days here, one day there etc - that would be excellent.
Dibs on this for the Part Two Reveal
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