how do tesla get 16A (5c) per 18650 3.1ah cell??

[toolman2]

the heading says it all,
with the new tesla s we find out that they are using panasonic NCR18650A cells (good to know as im not sure we ever really knew who made the current tesla cells?)

but now that we know, we can look up the specs like 3.1ah 3.6v (11.2wh per cell) -all good. (older 2.9ah cells)- http://sale.jtsgalaxy.com/ncr18650/

the trouble is the max c-rate, i have played the 18650 game on an e-bike before with 132 cells so i know how it plays out. roughly asking 1c or so is the maximum real world output that all of the higher capacity cells will happily do, sure you can double that at times, but when the cells are cold like 5deg c or less (common in heaps of places as an overnight temp -and you cant realisticly heat them overnight for a week) then you are back to a 1c max, and if you go any more then the cells fall below 2.5v, tripping the bms or losing up to a volt per cell!

but the new model s has about 220kw max power (say electrical power into the motor?) and the smaller pack is 42kwh, if you want 220kw from this pack then you are asking about 55w per cell (about 4000cells vs 8000cells for the biggest pack) -when they are loaded like this the voltage will drop to about 3.3v as the ir is about .06ohms, so they are pulling over 16 amps from each cell! AND losing about a volt (ie a 380v pack is now 280volts!)
and thats when the cells are NEW -ask me if it got better after a year or 2 :wink:

these are the finest ev's around and there are heaps of good reasons for them and us to use these cells -like a massive 248wh per kg!, try working out how many of these 45gram cells YOU could have on board, the resulting capacity and the way you can have so many of them that even the c-rate problem could kinda remain acceptable..

many of us could make use of the goodness and world leading energy density of these cell BUT something doesnt quite add up right though so it would be good to hear some other takes on this?

 

[dogman dan]

Aren't the panasonic cells pretty good stuff? 5 c wouldn't suprise me for good lifepo4. What chemistry are those?

 

[Nuts&Volts]

I'm pretty sure the cells are LiCo just like some RC lipo batteries, so I would believe they can do a lot better than 1C.

Also I know Panasonic is working on some Lithium Nickel cells for future Teslas.

-Kyle

 

[grindz145]

They are LiCo cells. Theres no way they could get the density otherwise. As far as I can tell, they get away with that because they cool the heck out of them. There's no other way these cells could do that on their own. That's one of the reasons why I hold Tesla in such high regard. They really did some engineering. It's certainly not just slapping an electric motor and some cells into a Lotus...


Edit: did I mention that their water cooling system along draws a few hundred watts (from memory).

 

[John in CR]

If I had a Lotus, that's exactly what I'd do...slap an electric motor and a shitload of cells in it. Ooops! Forgot the controller. I don't need the same kind of range and wouldn't have to build it so any retard with a drivers' license could use it, so where they need a heavy metal box and active cooling, I could get away with temp monitoring, making the whole thing relatively simple.

FWIW, From Tesla's website I come up with 2.2ah 18650cells and peak discharge at 3.8c . Both seem pretty reasonable to me. The 18650's I use are only 1.5ah but are much higher power, but that's because toolpack use is much more demanding than 3.8c with active cooling.

 

[dogman dan]

That's what I was thinking, the cells are not comparable to the cheap 18650 cells in some lifepo4 packs.

 

[toolman2]

They are LiCo cells. Theres no way they could get the density otherwise. As far as I can tell, they get away with that because they cool the heck out of them. There's no other way these cells could do that on their own. That's one of the reasons why I hold Tesla in such high regard.

yep, they are lithium-ion cobalt cells just like nearly all laptop cells, and this type (the very highest capacity ones) are the ones that normally have the lowest peak current rating -this is allways the tradeoff compared to other types with say half the capacity and 5 or 10 times the c-rating.
even panasonic themselves seem to advise 2c max not 5..

and its not cooling thats needed to get max current without severe voltage drop -quite the opposite. the biggest drama you have to there is when you gas it after a cold night and the low cell temps give you massive voltage drop, after witch i must admit the cells self heat, perform better, THEN need cooling.

but if the cells are really capable of 5c, and i believe they do have 248wh per kg, then why aren't we all using them -the fact is that most of the cells we all use are 2 or 3 times this weight for the same capacity and i think the panasonics (at least 2.9ah) can be had for $5ish each, so to my mind we have to gain a little more of an understanding here and possibly move miles ahead. :wink:

how are our battery needs so different to teslas? -i know some of us just want short busts of big power from lipos, thats ok but trust me it really is good and so much easier to live with when your ev in real day to day life when its got heaps of spare range.

 

[toolman2]

btw dogman, these cells are not that expensive: http://au.alibaba.com/product/333211445-NCR-18650-panasonic-18650-2900mah-3.html
you would actually struggle to get any cheaper ah per $ than these cells.

18650's are not what you find inside cheap lifep04 packs, but not to worry, these panasonics are acctually even cheaper than them..

 

[grindz145]

and its not cooling thats needed to get max current without severe voltage drop -quite the opposite. the biggest drama you have to there is when you gas it after a cold night and the low cell temps give you massive voltage drop, after witch i must admit the cells self heat, perform better, THEN need cooling.

Very good point. There is active heating as well as I recall. There is a narrow temperature operating range for sure. There is a slight tax in volumetric energy density for LiPo, but the main reason I bet they are using good ole cylindrical cells is cost. Even Tesla has to consider cost. Especially if they ever plan to deliver a $40-50k model.

 

[MN Driver]

The Model S is not using LiCo cells in the Model S. Elon Musk has specifically discussed that it has been working with Panasonic to get a higher energy density Lithium cell that contains Nickel. There are videos on Youtube where he discusses this. I'll see if I can track one of them down.

Edit: Found a video discussing it.
http://www.youtube.com/watch?v=9cfHGDoniU0
Starting at 3:00 mark
This is basically what he said(with Umm's, uhh's, and the person asking questions removed: For the Roadster, we use an almost unmodified laptop cell, but for the Model S, it is actually a highly modified cell. It's an 18650 cell, so the external form factor is the same, so we can take advantage of the economies of scale of 18650 production, but the internals are quite different. More than that, I cannot say...

IMHO, Of course the details Elon gave us are vague but there are some chemistries out there like LiMnNiCo so it could be something like that. Of course if Panasonic just developed something, it's possible that Tesla could have the first and exclusive crack at it. Just like how Toyota/Lexus has the exclusive crack at the NiMh prismatic cells they are producing.

 

[picasso]

How does it get 5c....cooling and burst to only 5c.

"internals are quite different" as in some/all cells will get on-board circuits to take the cell in and out of the pack and or cells behind a master cell.

The decay starts from the time the cell is mfg'ed. And can go to 20% depending how it is stored.

I wonder how Tesla will deal with people who always keep the car charged...at 75F the cells will permanently lose about 20% a year when stored about 95% charge. That can be cut in half if you store it under 50% when not in use. so will we all need a huge charger at home to top off before we go for the day?

As for why most people dont use the 18650 cells. Id say just the amount of work needed to stitch them up, And a design to hold them rigid.

 

[grindz145]

The Model S is not using LiCo cells in the Model S. Elon Musk has specifically discussed that it has been working with Panasonic to get a higher energy density Lithium cell that contains Nickel. There are videos on Youtube where he discusses this. I'll see if I can track one of them down.

Edit: Found a video discussing it.
http://www.youtube.com/watch?v=9cfHGDoniU0
Starting at 3:00 mark
This is basically what he said(with Umm's, uhh's, and the person asking questions removed: For the Roadster, we use an almost unmodified laptop cell, but for the Model S, it is actually a highly modified cell. It's an 18650 cell, so the external form factor is the same, so we can take advantage of the economies of scale of 18650 production, but the internals are quite different. More than that, I cannot say...

IMHO, Of course the details Elon gave us are vague but there are some chemistries out there like LiMnNiCo so it could be something like that. Of course if Panasonic just developed something, it's possible that Tesla could have the first and exclusive crack at it. Just like how Toyota/Lexus has the exclusive crack at the NiMh prismatic cells they are producing.

Good info MN. My money would be on some form of LiMnNiCo. The LiMn2O4s have terrible energy density but these sound like a reasonable compromise. These won't be 3.1ah cells though and that explains in a nutshell why they'll have higher power density.

 

[spinningmagnets]

Good article recently on Tesla, Daimler (Mercedes) and Toyota becoming partners in "Wired" magazine. They post 'snippets' of the articles on the web to get you to buy the magazine. Things are looking good...

http://www.wired.com/autopia/2010/10/teslas-got-the-factory-now-it-needs-to-fill-it/

http://www.wired.com/autopia/2010/05/toyota-tesla-team-up-on-evs/

 

[Hillhater]

If I had a Lotus, that's exactly what I'd do...slap an electric motor and a shitload of cells in it. ...

why do that to a Lotus ??
you buy a lotus for its minimum compromise performance and handling, so why turn it into a slug with all that extra weight and complexity.

 

[texaspyro]

why do that to a Lotus ??
you buy a lotus for its minimum compromise performance and handling, so why turn it into a slug with all that extra weight and complexity.

'cause we know what would happen if Lucas did the electrics...

And I though one bought Lotus' because you like to support your local mechanic. A friend of mine bought a brand new Lotus. It went through three trannies in 12,000 miles. Also had to have the engine rebuilt. And he knows how to drive... and wasn't the only one with the same issues. But, damn, it had a nicest leather interior you could imagine!

 

[Hillhater]

A friend of mine bought a brand new Lotus. It went through three trannies in 12,000 miles. Also had to have the engine rebuilt. !

Odd, .. most of the current Lotus range use Toyota engines &Transmissions. !

 

[grindz145]

A friend of mine bought a brand new Lotus. It went through three trannies in 12,000 miles. Also had to have the engine rebuilt. !

Odd, .. most of the current Lotus range use Toyota engines &Transmissions. !

Engineering design limits are important....

A Lotus is a mediocre car for a yuppie who can't afford a really good car anyway.

A Tesla is revolutionary, with 400x the engineering. Petrol engines are boring.

 

[Hillhater]

OR,
..A Lotus is a CAR for enthusiasts who understand and appreciates usable performance in a practical vehicle at a realistic price..
..a Tesla is an expensive novelty for those with more money than sense and wish to be early adopters of every new toy, practical or not !

 

[liveforphysics]

why do that to a Lotus ??
you buy a lotus for its minimum compromise performance and handling, so why turn it into a slug with all that extra weight and complexity.

'cause we know what would happen if Lucas did the electrics...

And I though one bought Lotus' because you like to support your local mechanic. A friend of mine bought a brand new Lotus. It went through three trannies in 12,000 miles. Also had to have the engine rebuilt. And he knows how to drive... and wasn't the only one with the same issues. But, damn, it had a nicest leather interior you could imagine!

This is why the ONLY lotus to buy is the elise.
Toyota celica drivetrain.

 

[toolman2]

interesting the tesla dude saying they are a modified laptop cell, as 3.1ah they are going to use is the absolute max (of an 18650) and that allways means lower c-rate (the high c-rate ones are about half that capacity).

panasonic have the specs up for the 3.1ah cells, and it leaves me wondering if thats them or not, i spose (maby) its possible to make a special 3.1ah AND high c-rate cell at much higher cost but clearly even for tesla the cost of cells is a massive part of the build components -even standard cells..

anyway, i got a quote back for $4.50 per cell for (200 of) the 2.9ah panasonics, still kinda interesting cos you still get 232wh per kg (double or more for the same kg of most ev cells) AND maby also the cheapest at $1.55 per ah. your right though picasso, its an effort.

so what are the finest higher than 2c cells around at present? (might leave lipos out ) still the a123 prismatics ? are people still chasing them? can anyone get them now?? (happy with my a123 20ah's with the EXACT same capacity and ir as new after 100+ cycles)

 

[Hillhater]

This is why the ONLY lotus to buy is the elise.
Toyota celica drivetrain.

Or the Evora with the V6 Aurion drive train. ( but not as nimble !)

 

[texaspyro]

Odd, .. most of the current Lotus range use Toyota engines &Transmissions. !

His was a Turbo Esprit from about 20-25 years ago. His first one got jacked (before it was fashionable) and was recovered partially stripped and burned to a crisp. Didn't learn his lesson and got another one. It's gotta be that sexy leather interior that rots your common sense brain cells.