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How fast would a P40D be?!

Sunlight

Member
May 7, 2014
331
777
South Africa
We all know that weight affects acceleration and cornering. I understand that the batteries make up nearly a third of the weight of a P85 - presumably the 60 is proportionally lighter.

How fast would a Model S be with half the battery load?!

P40D - 0 - 60mph in, what, 2.8secs?

OK I know the range would let it down but...............
 

Saghost

Well-Known Member
Oct 9, 2013
8,224
7,087
Delaware
Like Stoneymonster was saying, the rate of charge or discharge of a battery is generally expressed as a function of the nominal capacity - a "1C" rate of charge or discharge is fully filling or draining the battery in 1 hour - so an 85 kW draw on an 85 kWh battery.

Lithium batteries are more tolerant than most, but they have limits, too. The P85D's rated 515 kW is a 6C load - very much on the high end for storage chemistries, and a close match for the Volt's 7C 110 kW maximum on its much smaller 16 kWh battery.

To sustain 515 kW on 40 kWh would be a 13C load - well up into LiPo only territory (Tesla could build a pack to handle this, but it'd be more expensive cells with lower energy density and worse cycle lives - all about the tradeoffs.)

Incidentally, you do know that the current 40 kWh cars are 60 kWh batteries with artificial charge limits, right? Tesla had so few orders for it they didn't think it was worth the money to make a separate pack design. So with the existing packs there's no difference in weight or power output between an S40 or S60, nor your proposed P40D and a P60D.

Of course, the existing pack won't give you what you wanted anyway...
Walter
 

SabrToothSqrl

Active Member
Dec 5, 2014
3,878
3,302
PA
If I recall my Tesla Motors history correctly, the MS with a 40kWh battery never happened. It was a 60kWh battery that was software limited to act like a 40kWh because Tesla didn't want to clog the pipeline for so few orders.


I believe you are correct. the uptake on the 40 was very low... no need to make a part that only 10% of people buy. Scaling the larger one will be cheaper all around.
 

Solarwind

Member
Jan 31, 2015
67
65
Power MT
Like Stoneymonster was saying, the rate of charge or discharge of a battery is generally expressed as a function of the nominal capacity - a "1C" rate of charge or discharge is fully filling or draining the battery in 1 hour - so an 85 kW draw on an 85 kWh battery. Lithium batteries are more tolerant than most, but they have limits, too. The P85D's rated 515 kW is a 6C load - very much on the high end for storage chemistries, and a close match for the Volt's 7C 110 kW maximum on its much smaller 16 kWh battery.To sustain 515 kW on 40 kWh would be a 13C load - well up into LiPo only territory (Tesla could build a pack to handle this, but it'd be more expensive cells with lower energy density and worse cycle lives - all about the tradeoffs.)Incidentally, you do know that the current 40 kWh cars are 60 kWh batteries with artificial charge limits, right? Tesla had so few orders for it they didn't think it was worth the money to make a separate pack design. So with the existing packs there's no difference in weight or power output between an S40 or S60, nor your proposed P40D and a P60D. Of course, the existing pack won't give you what you wanted anyway...Walter
Very good explanation thanks! Question, why on our P85D with a cold battery, it seem to take forever to get full regenerative braking but the acceleration seem not to take a hit.
 

Saghost

Well-Known Member
Oct 9, 2013
8,224
7,087
Delaware
Very good explanation thanks! Question, why on our P85D with a cold battery, it seem to take forever to get full regenerative braking but the acceleration seem not to take a hit.

I'm not an expert on battery chemistry by any means, but I've read that one of the things that kills lithium cells is charging them at low temperatures (cell temperatures below 32F I read one place?) - apparently it will plate pure lithium metal from the electrolyte onto the anode (or was it the cathode?) which causes irreversible capacity loss. Discharging the battery doesn't have a matching form of damage, however.

My guess is that Tesla is limiting the regeneration to prevent damaging the battery pack.
Walter
 

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