AGR said:
A full tank (battery pack) is 185Kwh
No, that isn't right. Pack sizes can have different capacities, but the Roadster's is about 56kWh (or was that 52kWh?).
That gives an idea of how much total energy charge it can store.
They use the "C" value of the batteries to show how many time capacity they can output as continuous watts.
So for simplicity sake lets say that the pack stored 50kWh, and the batteries could do 4C.
Then the pack could output 200kW for 15 minutes, or 100kW for 1/2 an hour (at 2C)..., or 50kW for one hour (at 1C) (thus 50kWh). Using the battery C values isn't like direct math. You sort of "cheat" with shorthand that drops the hour rating to calculate the instantaneous output possible. The C factor is used to show max possible current draw, but the batteries are happier if you draw less current, so 4C capable batteries are given an easy time if you only need to draw 1C. Drawing current too fast can damage the batteries and shorten their lifespan.
With the Roadster, if you asked the eMotor to make 185kW (248hp) continuously, a full pack would be empty in 18 minutes (56/185*60). People have done rough calculations predicting that the Roadster might need 110kW to maintain 130mph, so at 130mph (max speed) it may be able to travel about 65 miles ( (56/110*60)=30 minutes... (130mph*30/60=65 miles. )
as the battery pack loses charge the HP goes down.
Probably not as much as you think.
An "empty" pack still has a lot of voltage left. A full Roadster pack might output ~410Volts, and then down to 300Volts when considered empty. Even if they were trying to use max pack voltage all the time (which I don't think they do) they could still probably try to draw more amps from the cells even when their voltage is down. So, I don't really know how it works, but I suspect the power output from a full pack is not a huge amount different from a "so called" empty pack. With different programming they could probably extend the range even more, but then the pack is drained past the point where it damages the batteries and they don't want to take a charge again.
You can read some more about their batteries here:
http://www.teslamotors.com/blog2/index.php?p=39&
http://www.teslamotors.com/display_data/TeslaRoadsterBatterySystem.pdf
You can configure this battery pack to deliver power in a variety of ways as per the application.
Well it isn't exactly modular and so easily reconfigurable on short notice, but with some re-engineering time it could be re-made for a different application
One way to configure the battery pack would be for a portion of the pack to run all the accessories, and another portion to run the motor.
They have a voltage converter that can lower the pack voltage to something appropriate for the accessories. So they don't need to segregate the pack as you say. Both the accessories and the drive motor share the same stored charge.
You could order a car with a "performance" - "cruising" - "commuting" battery pack formats.
Well, yes, that has been suggested, but so far they only seem to have the one pack offered.
If you read up on the
Lightning GT you will find that they offer different models with different packs. They have a high performance, short range version, as well as an "extended range" model with less performance.
Usually when things get hot the durability / longevity is affected...
The back side of the elctric motor with less air flow could be at a higher temperature.
I am sure they are keenly aware of any such issues. I think there is a big fan and ductwork to get good airflow where it needs to be.
I would conclude that the design parameters of the electric motor are such that it can operate under close to full load for many many miles.
Induction AC motors can be extremely reliable. They power most freight trains for instance (with a Diesel generator to provide electricity).
If Tesla did all their homework the eMotor should last the life of the car.