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RobStark
Well-Known Member
Bangor Bob
Member
Well then it's just a crap design. Residential minisplits can have HSPF's of 12, COP's > 1 down to -15F, and SEER ratings in the 30's. No reason a Mitsubishi or Fujitsu 12kBTU minisplit can't be repackaged for automotive use - the outdoor heat exchanger is really the only bulky component.
The Leaf has a "hybrid heating system", i.e. a heat pump, so it's performance is relevant in terms of the technology. Nissan published a graph showing benefit by temperature and it wouldn't help in deep winter morning commutes here.
The car and the Supercharger network have to meet those regular needs.
That does not make sense. If 40kWh is enough for regular driving, then you can charge a 50kWh battery at only a slightly higher rate than the 40kWh for the same effect. (Extra weight reduces efficiency).
And I'm not making comparisons with the S/X battery. I'm simply using the fundamental rule that you can charge larger batteries faster. Tesla has said that they want to speed up Supercharging and there's an obvious need both for capacity and customer convenience. Faster charging is better. More range is better. Both reduce the cost of the Supercharger network. Both reduce OTR charging needs and shorten journey times. Customer gets better utility, Tesla lowers costs. Tesla wants to sell more battery and sell you their Supercharger network. The base model needs to cut out the frills, not the utility. Long-distance BEV is what separates Tesla from the other manufacturers. (Even Audi's 150kW PR blitz is rather light on the network fundamentals, and once again journalists failed to push them on their whole vision of it). There will be more competition from other manufacturers for people who just want a long-range BEV.
Bangor Bob
Member
A lot of the cues from that ended up in the EV1. The EV1 was a clumsy execution, but the ideas were there. (And it hit .195Cd, as I recall).
There are tiny bits of that appearing in a lot of cars these days - mostly the front-rear tapering greenhouse profile, and a degree of Kammback -ness. One downside of a Kammback is that the rear of the car is always filthy. Also in the winter loose snow accumulates on the vertical rear surface and can obscure the taillights after driving just a few miles.
Rashomon
Member
It comes down to range miles per minute of charge. A more efficient vehicle, say a more aerodynamic one, will get more miles per kWh of energy. Yes, at the same C rate you can dump more energy into a large pack than a small one. But that doesn't mean a more efficient vehicle with a smaller pack won't actually charge at a faster rate when measured in miles/minute. And it will either cost less or have higher margin for the manufacturer than the less efficient vehicle.
Musk is smart; he's obsessing about CdA for a reason.
stopcrazypp
Well-Known Member
Improvements in CdA and other efficiency measures should not come with significant reductions in battery capacity. You end up with a car that gets good range in certain conditions and then a large drop in other conditions. Increasing battery capacity increase range linearly with the capacity in practically all conditions. However, measures for increasing efficiency only work in certain conditions and is less reliable.
Given dropping battery costs and improving energy density, it does not makes sense to start with a small battery pack. Besides from lower charge and discharge power as mentioned, a smaller battery pack also will be stressed more for the same amount of range traveled and will last a shorter amount of miles. I would not expect anything under 50kWh.
Given dropping battery costs and improving energy density, it does not makes sense to start with a small battery pack. Besides from lower charge and discharge power as mentioned, a smaller battery pack also will be stressed more for the same amount of range traveled and will last a shorter amount of miles. I would not expect anything under 50kWh.
BriansTesla
Old school meets new tech
I think it is worth considering here that many buyers of the M3 might be willing to have less battery capacity to have a car they can afford. They might keep their 10 year old car for road trips and drive their $35,000 M3 for everything else. A couple thousand dollars are important here. Other buyers could still have their 275-300 mile loaded M3.
A 50kwh battery might turn out to be the best number.
Supercharging mph on the S: 85 > 70 > 60. Having 40kWh instead of 50kWh would reduce the maximum charging power by 25%. Cutting 10kWh would not make the car 25% more efficient.
I'm not saying they shouldn't push aero. I absolutely think they should. Aero provides utility. My point is that they shouldn't be using extreme aero as a way to cut battery size significantly, because that has negative implications for utility and for the cost of the Supercharger network.
And one thing I hadn't mentioned was degradation. 70% of 40 is 28.
stopcrazypp
Well-Known Member
On the subject of battery cost, difference between 40kWh and 50kWh is 10kWh. At $200/kWh at the pack level every 10kWh costs $2000. Tesla is targeting below $100/kWh in long term with Giga factory which would be $1000 per 10 kWh. That is $1000-2000 difference in cost. How much more money Tesla would have to spend to squeeze another 20% more efficiency out of the vehicle? I'm not convinced it will be significantly less.
Elon has been adamant the car will get 200 miles at minimum in real world conditions. The most efficient EV (the i3) uses 18.8kWh to get 81 miles of EPA range. That's 232Wh/mi. Even assuming absolutely zero buffer (actual battery size for the i3 is 22kWh), that requires 46.4kWh to get 200 miles EPA. While I expect the Cd of the Model 3 to be better (i3 is 0.29), the frontal area will likely be larger. Also Tesla won't be using the extreme weight reduction and skinny tires the i3 uses. I am simply not seeing 200 real world miles from a nameplate 40kWh capacity.
Again, we're talking about the lowest end affordable car. $1000 makes a difference. At this price level, you are likely to get buyers who are weighed more heavily on a pure financial decision, they are less likely to max out their options. I for sure see the marketing material boast how much cheaper it is to operate this car versus an ICE.
The effect of weight on real world range appears to be minor, which makes sense if your total efficiency through regen is high, and I expect further refinements to driveline efficiency with the 3rd gen motor/inverter.
Pushing the air around is what takes the most power. It would be silly NOT to focus your engineering effort on fixing the single largest drain of power.
stopcrazypp
Well-Known Member
I'm not saying they should not be focused an aero improvements. I'm saying whatever improvements they make should be on top of the pack size (I expect minimum 50kWh). I do not think it is a good idea to use it as a way to cut down pack size to 40kWh. Ultimately I don't think the Model 3 can reach 200 miles real world range with a 40kWh pack, esp. if you are talking about spending less than $1000-2000 to do it. It seems to me much easier to have the pack be 50kWh and it might not even be any more expensive than a car with 40kWh that was optimized extensively.
Aero largely helps highway range, but in mixed driving the weight also plays a role. If you look at a EV efficiency, you will notice Tesla is the only make where highway efficiency is higher than city efficiency.
http://insideevs.com/bmw-i3-bev-official-epa-rating-range-81-mpge-124/
Arguing about the final pack size is silly without knowing the engineering that goes into the whole system is silly. I only calculated 40kWh to get an idea of what amount of energy they would need to deliver on 200 miles range. Note That Tesla themselves had almost delivered a Model S in 40kWh. But arguments against supercharging and heating are based entirely on current generation cells and technology. Why assume these will stay the same? Energy and power density are somewhat independently select-able, for example. Especially if you own the biggest battery factory in the world.
They've said repeatedly there will be new technology and it will not be simply a 20% smaller model S.
stopcrazypp
Well-Known Member
The 40kWh Model S (160 miles ideal range, 142 miles EPA) was determined to be un-viable though by Tesla. And back then Elon didn't make any hard promises of a 200 mile minimum range (and real world on that). Elon did for the Model 3.
We can throw aside the exact numbers, but given the same chemistry, the power will always go up linearly with the capacity. When you select a power optimized chemistry, the energy density goes down. Those fundamental trade-offs are always there. The reason Tesla was able to make such long range EVs is that they selected the most energy dense cells they can find and made a pack large enough to meet their power requirements. And they reaped the benefits of the larger pack in terms of reduced degradation. Given their commitment to small cell cylindrical, I don't see them straying from this approach. I would be very surprised if the Model 3 pack was not a small cell cylindrical and NCA chemistry.
Model 3 deliveries are planned for late 2017, cell production at Gigafactory originally planned for 2017, but schedule has been pushed up to late 2016. Tesla simply doesn't have the time to pick a radically different chemistry.
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~4 years ago for a car that was a Model S, not a Model 3. Again, in the past. Future = different
Power density and DCIR is more related to electrode surface area than chemistry. They reduce cell energy because more of the volume of the cell is dedicated to the electrode vs electrolyte.
They've already changed chemistries twice^H^H^H^H^Hthrice in several years...
You're being very resistant to change...
No he isn't.
Until the 90, the Model S battery packs used a single chemistry, but a different number of cells in 60, 70 and 85. The 90 packs use a newer chemistry. If you want to minimize cost, then having a different cell would be a hindrance because of additional development, manufacturing and support costs. To minimize cost on a smaller pack they'd have to do the same as the S and have the same chemistry, but fewer cells, and then it would charge more slowly, just like the 60 was slower than the 70 is slower than the 85.
Slower charging, less range, less tolerance for poor conditions, higher C rates, lower maximum kW output, higher proportion of Supercharged miles, higher SoC charges, lower SoC discharges, and less tolerance for degradation.
Capacity is the _last_ thing that should be sacrificed to meet price targets.
stopcrazypp
Well-Known Member
No, I'm not resistance to change. The only massive change they made in chemistry was from LCO to NCA from Roadster to Model S.
The partial silicon anode on the 90kWh is only a moderate change. I expect a similar moderate change for the Model 3, but it's not going to fundamentally change things such that a 40kWh battery makes more sense than a 50kWh battery (or something roughly in that area as you suggest). Like ItsNotAboutTheMoney puts it, I just think cutting minimum capacity is horrible idea regardless of how chemistry changes.
JRP3
Hyperactive Member
We also have to remember they need to lock in a cell chemistry which is fully tested well before the first car is built, so they may have a year or less of more cell chemistry development. As far as minimum pack capacity I've been leaning towards 50kW.
NO! This is the the the thoughts behind every short-range EV, and the TMS40. Tesla is on a mission to deliver a mid- to long-range EV's that should be able to replace the old fossil burning cars. So no, even the base $35,000 TM3 will be able to go from supercharger to supercharger, witch will say at least > 200km range under (almost) all conditions. The supercharger access may still be an option you have to pay extra for (but I hope not
).
