How is Tesla charging the Panasonic 18650PF at over a 1C rate?

VRdublove · Jun 27, 2014

This is my first post on the forums, what a fantastic community!

My question relates to Tesla's fast charging of Panasonic cells.

Every spec sheet that I've seen from Panasonic lists the maximum charge rate as 0.5-0.7C. With Tesla's 120kW Superchargers, they would be charging at 1.41C. Are they accomplishing this through active thermal management? Surely you can charge a battery faster than its suggested charge rate, but I would expect reduced lifespan of the battery. Is temperature management the only thing that limits the maximum suggested charge rate of these cells?

It's my understanding that the Model S uses the Panasonic 18650PF cell, which has an DC resistance of around 43 mOhms. Other 18650 cells in the industry with similar internal resistance numbers are rated for a 1C max charge rate. I'm wondering if Panasonic is rating their cells to a reduced charge rate in order to maximize cycle life to 80% of initial capacity.

I expect that because Tesla is using a liquid cooling system, it can safely support a faster charge rate, with minimal added stress on the cells. I imagine that the standard 0.7C rate is with the expectation that most applications of this cell are for power tools in sealed enclosures, so the charge rate is reduced to manage temperature, and increase safety margins since cooling is only passive.

Can any one firm up my speculations?

Cheers,
Tommy

Cosmacelf · Jun 27, 2014

Yes Tesla uses active liquid cooling. You especially notice it during Supercharging when the pumps and AC turn on. Also the specific cell that is used in the Model S isn't a generic Panasonic cell. It is a custom one and AFAIK, no one outside of Panasonic and Tesla knows the exact specs.

Teo · Jun 27, 2014

Besides liquid cooling, the batteries also have a custom chemistry which helps with battery life. By the way in Europe superchargers are 135 kW. The most technical video that I know of about Tesla batteries is this one:

stopcrazypp · Jun 27, 2014

VRdublove said:
It's my understanding that the Model S uses the Panasonic 18650PF cell, which has an DC resistance of around 43 mOhms.

Tesla's cells are custom built. They don't just use off the shelf cells. You can use the spec sheets of those type of cells as a basis for rough comparison, but can't use the exact specs and expect them to be the same.

Also we already know that for the 85kWh pack, Tesla is using 3400mAh cells, so it can't be the 18650PF anyways (at 2900mAh).

LMB · Jun 27, 2014

(LMB spouse)

It's also true that the maximum charge rate only occurs when the battery is at less than 30% of capacity. By 50% capacity, the charge rate is less than 1C and declines steadily until the battery is as full as Tesla allows. If you've ever done a range charge at a Supercharger, you know that the last 25 miles take a *long* time.

djp · Jun 27, 2014

The cells can be charged faster at low state of charge. The SuperChargers ramp down as the battery charges, they're not charging at 1.4C all the way to the top.

Electric700 · Jun 27, 2014

What is the C in 1.4 C? Is that related to temperature (Celsius), amps, volts or something else?

djp said:
The cells can be charged faster at low state of charge. The SuperChargers ramp down as the battery charges, they're not charging at 1.4C all the way to the top.

trils0n · Jun 27, 2014

1C = total capacity in 1hr

UberEV1 · Jun 27, 2014

"C" = Couloumb. From Wikipedia . . .
The coulomb (named after Charles-Augustin de Coulomb, unit symbol: C) is a fundamental unit of electrical charge, and is also the SI derived unit of electric charge (symbol: Q or q). It is equal to the charge of approximately 6.241×10[SUP]18[/SUP] electrons.
Its SI definition is the charge transported by a constant current of one ampere in one second:

David99 · Jun 27, 2014

"C" is this case stands for capacity (not 'coulomb'). A battery capacity is measured in Ampere-hours (Ah). A single AA rechargeable cell for example has 2 Ah. The charge/discharge rate is relative to the capacity. If the battery is charged at 2 Ampere, that is called 1C. If the battery is charged at 1 Ampere it would be 0.5C. If the battery is charged at 4 Ampere it is 2C. And so on. By using this value (charge/discharge current relative to capacity) it is easy to compare different size battery systems.

N4HHE · Jun 27, 2014

A modern NiMH AA cell can have a 2 Ah capacity but historically NiCAD AA was in the 300 to 600 mAh range.

Matias · Jun 28, 2014

Teo said:
By the way in Europe superchargers are 135 kW.

Is that enabled at the moment?

- - - Updated - - -

About high C rate:as many have pointed out, charging with full power is only possible, when battery is empty. Here is more info from blogger with Tesla's coments ( in red):

http://teslaowner.wordpress.com/2014/01/01/supercharger-time-test/

ch_model_s · Jun 28, 2014

Matias said:
Is that enabled at the moment?

No.. we only get about 108kW in Europe right now....

Matias · Jun 28, 2014

ch_model_s said:
No.. we only get about 108kW in Europe right now....

Why not 120?

Muzzman1 · Jun 28, 2014

I can not find the thread for the life of me, but I'm fairly certain that someone on this determined that even at 135kwh the charge rate is much less that 1C.
Anyone here know what thread I'm talking about?

Electric700 · Jun 28, 2014

Thanks for clearing this up!

David99 said:
"C" is this case stands for capacity (not 'coulomb'). A battery capacity is measured in Ampere-hours (Ah). A single AA rechargeable cell for example has 2 Ah. The charge/discharge rate is relative to the capacity. If the battery is charged at 2 Ampere, that is called 1C. If the battery is charged at 1 Ampere it would be 0.5C. If the battery is charged at 4 Ampere it is 2C. And so on. By using this value (charge/discharge current relative to capacity) it is easy to compare different size battery systems.

Cosmacelf · Jun 28, 2014

Muzzman1 said:
I can not find the thread for the life of me, but I'm fairly certain that someone on this determined that even at 135kwh the charge rate is much less that 1C.
Anyone here know what thread I'm talking about?

It can't be less. The entire battery pack contains 85 kWh of energy. So an 85 kW Supercharger would fill an empty pack in one hour. Which is 1C.

135 kW of power would charge it at 135/85= 1.6C

UberEV1 · Jun 29, 2014

David99 said:
"C" is this case stands for capacity (not 'coulomb'). A battery capacity is measured in Ampere-hours (Ah). A single AA rechargeable cell for example has 2 Ah. The charge/discharge rate is relative to the capacity. If the battery is charged at 2 Ampere, that is called 1C. If the battery is charged at 1 Ampere it would be 0.5C. If the battery is charged at 4 Ampere it is 2C. And so on. By using this value (charge/discharge current relative to capacity) it is easy to compare different size battery systems.

@David99: Thank you for clarifying and introducing a concept new to me. Hard to believe after all the threads I have read here that I missed this one. Thanks!

trils0n said:
1C = total capacity in 1hr

@trils0n: My apologies for the incorrect correction.

jkirkebo · Jun 29, 2014

Matias said:
Why not 120?

At least 122kW has been reported, but only at the newer sites like those in Denmark.

green1 · Jun 29, 2014

There have been reports of many 135kW chargers, but it seems that they are being used to allow more charge to the second stall rather than the full 135kW to one vehicle. max charge rate for a single vehicle seems to be in the 120-125kW range.

How is Tesla charging the Panasonic 18650PF at over a 1C rate?

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