Try looking at what the internal geometry of cylindrical cell looks like first before making totally wrongheaded analogies. There isn't a wire going down it. It's a rolled thin film cathode/electrolyte/anode.
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New Pack Architecture that is Likely Used in P100D and New TE Products
- Thread starter vgrinshpun
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- Tesla Inc.
Try looking at what the internal geometry of cylindrical cell looks like first before making totally wrongheaded analogies. There isn't a wire going down it. It's a rolled thin film cathode/electrolyte/anode.
LargeHamCollider
Battery cells != scalable
Imagine a very thin (1/150") sheet of copper foil with a 1/30" layer of plastic on top. The copper foil and plastic composite piece is 2.4 inches wide and 2 feet long. This sheet is rolled up to make a cylindrical shape that's about an inch in diameter and 2.4" tall. This is the basic structure of a cylindrical battery cell.
The copper is about 19,000x more conductive than the plastic, so, if heat is applied midway up the cylinder the heat will flow from the exterior end of the copper foil to the interior end along the spiral path (along a distance of about 2 feet) about 5x more readily than it will flow through ONE of the 1/30" plastic layers. So keep this in mind, the "shortest" thermal path to the most thermally distant point (the center of the cell) goes through two feet of copper foil.
Compare this to heat applied to the bottom of the cell, it only needs to travel the comparatively short 2.4" distance to get to the most "thermally distant" point, which is the top of the cell, additionally it has 10x (two feet vs. 2.4") the cross section to flow through so potential heat transfer from the heat source to the most thermally distant point is 100x what it was when we tried to get from a side of the cell to the center.
Obviously this example is hugely simplified, there are many confounding factors that prevent it from being as simple as I described it, the electrolyte/separator is going to be more conductive than straight plastic but this should give a general idea of what I'm thinking is going on [and having typed this I see you now have lovely diagrams above. Edit: and the video shows the roll structure, sweet.]
stopcrazypp
Well-Known Member
He is point is quite clear to me (he is not saying there is a wire, but it can be thought it that way in terms of conducting heat), but it seems to have flew over your head. JRP3 has discussed cells previously and it's extremely clear he knows all about the the jelly roll structure. It's actually a very good point that I missed previously.
What he is saying is that for the bottom cooled cell, the thermal interface has contact with all the anode and cathode layers directly.
In the old design, it only has contact with the outer layer and has to go through all the separator layers to reach through all the cell layers. From the own diagrams that you attached, you can see going from center to the outer layers of the cell has as much as a temperature gradient as going from middle to top even thought the distances are much shorter. This is likely because the separators serve as thermal insulators that slow down the spread of heat.
A picture tells things better so I have made a diagram that shows the differences:
The orange square part is the old thermal interface. You can see that it only will have contact with one layer and has to go through many separator layers to reach the middle.
The blue circle (the wider part representing the larger 2170 cell) is the new thermal interface. It has a direct path (no other layers in between) to every single layer in the cell.
If you rolled out the jelly roll into a flat sheet to see the thermal gradients, I'm not seeing how it's entirely clear that the old design would be better than the new, esp. once you factor in the separators.
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Another way to visualize that new cooling of the bottom of the cylindrical cell is way better than cooling through the portion of the side of the cell is to take a look at unrolled spirally wound terminals. New contact area as was mentioned above includes BOTH terminals along the whole spiral wound length (magenta), while old cooling area is just on the portion of the outside of the negative terminal (green).
New cooling from the bottom is clearly superior to the old cooing using ducts on the side of the cell. Really strange for anybody to be arguing the opposite.
New cooling from the bottom is clearly superior to the old cooing using ducts on the side of the cell. Really strange for anybody to be arguing the opposite.
JRP3
Hyperactive Member
You might want to consider why everyone else seems to understand exactly what I'm saying. I never said there was a wire in the cell, I was trying to create an analogy to better explain it to you. Obviously I failed.
I see what "everyone" is saying, I just think they're all wrong. Look at the thermal analysis above.
The thermal analysis supports JRP3. Let me demonstrate:
As you can see, distance from the bottom to the temperature indicated with orange (line B) is much longer than the distance from the sidewall to the same temperature (line A). This is because the heat is more efficiently being transported along the cell than across it.
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That's because of the heat dissipation properties of the cell in free air. Cooling it by the middle cools it nearest to the cell's hottest point.
Also, here's the kicker: You guys think the end of the foil connects to the bottom of the cell. IT DOES NOT. There is an anode tab that takes the vertical end of the foil and electrically connects. The rest of the end of the internal cell is floating above the end cap.
LOL
JRP3
Hyperactive Member
Yes, as pointed out, it supports exactly what I'm saying. The heat is being transported lengthwise faster over greater distance than it is across the cell, and it's not even reaching the side casing, but it is reaching the end cap.
JRP3
Hyperactive Member
By distance yes, but you keep ignoring the reality of the insulating properties of the various layers, as clearly shown in the diagrams.
No we don't.
I fail to see the humor in your mischaracterization of what is actually happening in the cell.
Clearly the heat is radiating along the 3 axes of the wound foil sheet in the cell.
Given that the entire width of the sheet (i.e. the entire "vertical" length of the cell) contains active material, the entire length of the cell is also generating heat. Yet in the images, the areas adjacent to the end caps are yellow, demonstrating that the caps are able to dissipate the heat load successfully.
Bottom cooling via the cap would appear to be just as efficient, if not more so, than that partial-contact sidewall cooling.
- The shortest axis (the thickness of the foil) is adjacent to the multiple insulating layers, which is an impediment to heat transfer to the "sides" of the cylindrical cells
- The longest axis (the length of the sheet), is wound "jelly-roll" style, and thus the heat has to spiral along the length outward to the outer side casing
- The last axis (the width" of the sheet is the one that is the shortest path to the outer cell material (the bottom cap) that does not have insulating material impeding heat transfer
Given that the entire width of the sheet (i.e. the entire "vertical" length of the cell) contains active material, the entire length of the cell is also generating heat. Yet in the images, the areas adjacent to the end caps are yellow, demonstrating that the caps are able to dissipate the heat load successfully.
Bottom cooling via the cap would appear to be just as efficient, if not more so, than that partial-contact sidewall cooling.
The Solar PV industry moved from 600V strings to 1000V strings and so using storage battery systems just under the solar PV voltage string max makes sense in the area of trying to DC charge right of the main voltage bus of a PV array. Storage DC-attached to the PV array strings should have less charging losses versus DC-AC-DC conversion to charge-up the storage units. To go sustainable, we can't just keep seeing systems throwing away 15%+ of the energy produced.
I think 350KW may be his claim for the supercharger unit itself, not each car. Current limits through one SC that share A/B connected cars limits the aggregate throughput. IT would be a monumental change to allow for one car to charge at 350KW - however, if A+B itself could equal 350KW aggregate that is more than double today's throughput. Doubling current throughput should be enough to be groundbreaking alone. We don't need a single-car to charge at 350KW unles it is in "convenience store" speeds of 5 minutes to add 100 miles for price-A and 200 miles for price-A * 3. I would suggest that shorter term recharging at high rates be done at consumer pricing but also to increase price as time goes by. Going for a "full charge" should have a higher cost per kWh than going for a "quick-hit" opportunity charge. If you could get 80-100 miles in 5 minutes and move on, that would be gas-station/convenience store level speeds and consumer-level. And at these speeds, battery swap certainly would never be considered when travelling - as they were not really an issue with 120KW supercharging either, but would make long range trips slightly more pleasant if the charging times were shorter.
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The humor is in working this hard to defend a design decision you don't even know that Tesla's made. The patent means nothing. Patents are filed for all sorts of ideas, the actual execution even if similar to the patent often has many details that were left out.
stopcrazypp
Well-Known Member
I'm seeing the same thing. Also, if you look at the other side with the rainbow colors, going from center of the cell to the casing, it transitions through all the colors (dark red to cyan-blue). This represents a temperature difference of 4-5 degrees over an extremely short distance. However, going from middle to top or bottom, it only transitions from dark red to yellow. This is only 2 degrees of temperature difference over a much longer distance.
The bottom cooling allows for BETTER control of temperature in each cell. This is the reason for faster supercharging in P100D.
It is irrelevant whether it was incorporated in new pack architecture or not. The bottom cooling provides for better temperature control of each individual cell, which results in more even temperature distribution within cell.
And BTW, you are by definition working several times HARDER than each of a half of a dozen people or so who are trying to educate you.
stopcrazypp
Well-Known Member
No, we don't think the end of the foil necessarily connects to the bottom (although you can design a cell that does that). However, the point about conduction between layers still stand. And given Tesla is having the cells custom made, they can make a thermally conductive but electrically insulating layer (same as the material used in the old design to interface between the coolant loop and cell casing) on the bottom to connect to the foil or they can use a continuous tab instead of a discrete tab in order to make it more conductive of heat.
