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Discussion in 'Model S' started by fiksegts, Aug 18, 2015.
could be faster since the P85D weighs less? how much weight does the extra 5 kWh add? :smile:
Both batteries weigh the same. The only change was very tiny amount of silicon used in place of some of the graphite in the graphite anode which allows the anode to suck up more lithium ions.
That said, silicon is know to reduce cycle life of Lithium Ion batteries. The maximum current shouldn't be any more on the 90 as that's not an advantage of silicon, but we don't know that they didn't make any other changes and even if both pull the same maximum current at 100% SOC, the voltage will be higher on the 90 battery after both have traveled x miles since the 90 will have a higher SOC than the 85. So it's fair to say that all being equal, the 90 will put more power down than the 85 after both have traveled 50 miles...as an example.
As I understand it, its not a situation of more cells, just more capacity with the same number of cells.
P85D and P90D may end up weighing about the same (give or take weight for options).
Technically the extra 5kWh would weight about 200 nanograms, according to Einstein.
I'm thinking this isn't going to cause much of a difference in the total weight of the car, though. hehe
I agree, they should perform the same...batteries should weigh the same and Elon said the limitation of the P85D is the fuse, not the power output of the pack....so I expect the same times.
....except for the "almost" that he added in there when saying they were entirely separate.
What about us P85Ds with staggered ?? U think that would give us additional grip at start ?
Isn't this whole discussion moot since the 90kWh upgrade is a prerequisite for Ludicrous mode? (ie: ludicrous P85Ds don't exist)
Only when purchasing a new PD. The existing P85Ds will get L without the battery upgrade for $5000 + labor (whatever that ends up being).
What is "cycle life" of battery?
Better cycle life = less degradation with each charge-discharge cycle.
Poor cycle life = degrades quickly with repeated charge-discharge.
Hopefully Tesla has solved this somehow. We'll probabaly hear some experiences in a few months.
The 90 and 85 kWh packs weigh exactly the same and they both have 7104 cells. The improvement is because of energy density increase. Elon explained this during the conference call. Listen from 8:39
Tesla Motors Ludicrous Mode Press Conference (Audio) 2015-07-17 - YouTube
8m39s Elon Musk: "We are shifting the cell chemistry for the upgraded pack cell to partially use silicon in the anode. This is just sort of a baby step in the direction of using silicon in the anode. Still primarily synthetic graphite but over time we will be using increasing amounts of silicon in the anode. The physical size of the pack from the outside will look exactly the same."
As various others have said there is no weight difference, other than the weight of the extra chrome underline on the rear badge
There's also no difference in maximum current, which is limited by the same fuse. And nominally the packs have the same voltage too.
However, there is an ongoing rumour that the P85DL (retrofit) takes 2.9s to do 0-60 against the P90DL doing 2.8s, and that the reason for that is that the new cells have a slightly lower internal resistance, which in turn means that the voltage drop on the larger pack will be fractionally lower at high current.
So for example a fully charged 85kWh pack outputting 1500A might have an effective voltage of 360V under load, whereas the 90kWh pack might have an effective voltage of 370V for the same load.
That would mean slightly higher peak power from the 90kWh pack, and potentially higher performance.
But this is all speculation; almost no P90DLs have been delivered, and literally no P85Ds have yet been retrofitted.
According to Elon the P85D insane mode is traction limited to about 30mph. With Ludicrous mode the increase in maximum amperage will extend the traction limited speed to somewhat higher, 60mph was mentioned but it is not really plausible. The quoted 0-60mph time reduction by 10-12% and the 0-100mph reduction suggest that the additional amperage has relatively more impact at higher speeds than at lower, where traction is not the limiting factor. Because we already know that the P85D 150mph speed can be maintained for only a few minutes before slowing to about 130mph, we can assume that either battery pack cooling, drivetrain cooling (presumably motors mostly) or both probably were the impediments.
We can safely assume that tesla is working on more efficient and effective cooling as well as increased temperature tolerance. Why: because Elon told us that Ludicrous came about as a result of efforts to design a 1,000,000 mile drivetrain and batteries. Thus, the use of high-precision fuses and high temperature capable steel alloys.
It seems logical, although nobody actually said it AFAIK, that the excellent results SpaceX has had with Inconel (BTW, a brand name for a class of stainless alloys, many of which are proprietary. Tesla appears to have a proprietary and undisclosed alloy, quite possibly the same as or derived from, the SpaceX experience. In my very humble opinion, the big news is really that Tesla is successfully conquering the heat management problems associated with high current movements.
Airbus, in their new electric trainers, are quietly deploying some connections that are claimed to be superconducting in ambient flying temperatures. Certainly Tesla is looking closely at that possibility. Putting any resistance reduction in combination with higher temperature handling will both increase performance and decrease energy waste, thus increasing battery longevity. Elon, announcing the 90kWh pack, said it had reduced internal resistance, and implied that was related to the embryonic silicon content in the anode.
Silicone anode and three-dimensional batteries (based on nano-technology to increase electron storage capacity by orders of magnitude) the holy grail in li-ion applications because the theoretical benefits of these technologies will revolutionize capacity, recharging, discharge speeds and more. The only problem is this has been known for years. The two articles I link here are years old. So far production costs, durability, stability and so on, have not yet been realized. Still, the 90kWh pack now has taken a baby step to real world benefits.
If I had the ability to get another Tesla I would buy the 90, not because of the 6% range improvement, but because it is the first mass deployment of silicon anode technology in an EV. Soon, we'll see better capabilities, but the stated capacities will rise, most likely, at roughly the 7% a year more or less that Elon stated. We probably will see greater concentration on cost reduction, durability and ease of use than we will in dramatic performance increases. At least until 2019 when Maximum Plaid will certainly arrive.
Silicon is heavier than carbon, so cells with more silicon are heavier. That makes 90 kWh battery heavier than 85 kWh, but not much. Perhaps only 90 kWh battery has Ludicrously low internal resistance.
If battery voltage drops from 400 to 370 V with 1500 A, then power loss is 45 kW. Loss cannot be much higher, or 2.8 s to 60 mph would not be possible. 30 V loss with 1500 A is so low that I don't believe it could be much lower.
Loss in motors similar, perhaps somewhere 40 - 100 kW. But transferring that heat away from motor is much easier, because motor (and engine) can stand much higher temperatures than battery. If air warms 50 C while passing through radiator, then 0.75 cubic meters air in second is needed to transfer 45 kW. Battery cannot (in summer) be 50 C warmer than air. If temp difference is 10 C, then 3.75 m³/s is needed. Radiator of MS is much too small.