Tesla Counters Top Gear's Claims & DOA Honda/Acura NSX
One memorable scene had Clarkson and the Top Gear crew pushing their first Roadster (they had two for testing) into the garage after apparently running out of juice. Or did they? According to Rachel Konrad, Senior Communications Manager at Tesla Motors, the car was most definitely not out of juice
( Read more... )
The only ways I see out are A) "Yes, we admit we didn't do the math and chose the wrong fuse. Fixed now." or B) it turns out that the fuse wasn't in the regenerative braking system. In which case they still have some explaining to do.
And yes an ultracap would be cool. How much faster would the car charge?
Well, I wouldn't advocate using one as the main energy storage for the car. So there'd be no effect on charging time - that's dependent on chemical reactions in the battery, and the addition of an ultracap won't change those.
What it would do, is to act like a moderator/buffer between the battery and motor. When you put the hammer down and the motor suddenly wants a lot of electrons, a charged ultracap can supply way more of them than the battery can (at least for a few seconds). Which means both better acceleration, and less load on the battery. Similarly, when the regenerative braking system wants to push a whole lot of electrons back into the battery, the ultracap can buffer the backflow. All told, adding an ultracap means that the battery can charge and discharge less rapidly, and have smaller current peaks. Both of which are really, really good things for battery life.
Ultracap as buffer = better battery life, better acceleration and better energy capture from regenerative braking. Only downside is cost. I don't even know what EEStor is charging for ultracaps, but doubtless it's in the thousands per. And I'm not sure if they're shipping units yet, either.
Reading up on EEStor, it looks like they're predicting ultracaps with an specific energy of 2.5 megajoules per kg. The Tesla's electric motor is a 185 kW motor, 80% efficient at peak power, and it goes 0-60 in 4 seconds. So worst case, 185 * 1/.8 * 4 = 925 kW. Wow, almost a megawatt!
925 kW is 3,330,000,000 joule/hours, but we're only running it for .001 hours. So that's only 3,700,000 joules, or 3.7 MJ. Two of EEStor's ultracaps in parallel should be able to take the Tesla from 0-60 no problem, without touching the battery. Once you lift the battery can start slowly recharging the cap, to get it ready for the next burst.
I'm too lazy to work the braking numbers. You can easily get the kinetic energy of the car from Ek = 1/2*mv^2. Since Ek is proportional to the square of velocity, I'd expect that at 2x the velocity, the car would have 4 times as much energy. Call it 15 MJ - 6 EEStor ultracaps to catch all that, assuming the regen braking can actually capture 100% of it (I doubt it's that high, but that's a good worst-case assumption to work with). That can be trickle charged back into the battery, or just kept in the ultracaps, ready for the next time you want to accelerate fast.
Reply
Still, the energy calculations should hold.
Reply
Reply
It's a conscious decision on their part. They're very much aware of the technology, but they just don't think it's ready for prime time yet - http://www.teslamotors.com/blog2/?p=24
unless the batteries are already that good?
Not even close. LiIon's have a specific energy of about 0.5 MJ
Reply
Reply
Leave a comment