JRP3

How do you figure? High speeds and hard acceleration takes more energy, no matter what the power plant. No amount of regen will recover energy lost to wind resistance and ground friction, and regen strong enough to lock the rear wheels won't help anything. There is no practical or reasonable use for ultracaps in the Roadster.

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TEG

To make the battery pack last longer?
(Although I suppose the calendar lifespan of the pack could run out before you hit the expected 500 cycle lifespan).

malcolm

Oh crap!

I thought it had to be tattooed on our butts.

I swear there was a memo.....

JRP3

Since the addition of caps would increase the price, I don't see that as a practical use. Also for the average driver I don't see the pack as being stressed that much without caps, so they would provide even less value. I suppose at some point the price of caps and the cost of integrating them into the pack could be low enough that they might provide a real world benefit but I don't think we are even close to that.

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Tim

Umm, you're right about wind resistance at high speed, but completely wrong about acceleration. It takes the same amount of energy to accelerate a car to a given speed regardless of the amount of time it takes. The only thing that changes is the power used. However, the nice thing about electric powerplants is that are only marginally less efficient delivering max torque than they are when running most efficiently. This is completely different from internal combustion engines which burn alot more fuel less efficiently to achieve high torque. You're right that there are limitations to the amount of regen that can be had from a RWD car, but the Tesla isn't anywhere close to that. However, by implementing more aggressive regen and using caps to minimize losses on the battery, you'd see much less degradation in range than would be typical for a regular car running the same stop and go track cycle. The average speed at the top gear track for the Tesla is about 70mph I think. You can guess at the average power usage over that time. Ideally, if it were to regen completely on all four wheels, its range should only be marginally less than the graph given by JB(less due to non-linear increase in wind resistance) for that speed.

Clearly, the Tesla is not close to ideal in this respect, and I think that using supercaps to maximize regen and minimize high C discharges would be beneficial in moving closer to the ideal. For running an oval track at a constant 120 mph, then of course you're correct that supercaps won't have any benefit.

However, when I see Carmack's and Martin's real world range numbers, I have to think that this is isn't due to them averaging 80mph per trip(which might be the case), but more due to jack rabbit starts and stops to show off the Tesla's acceleration. For this kind of driving behavior(and for the Top Gear track) caps would very much improve range.

JRP3

I think even with an electric motor hard acceleration will draw more amperage, which means more heat build up, which means less efficiency. A vehicle will slow down even without braking or regen because of drive train and road friction as well as wind resistance, you can't recover that energy. Hard cornering will also slow you down without braking, because of friction, which is also lost energy you can't recover.
As for real world hard acceleration affecting range, caps won't help much since most people will accelerate hard to show off the power, or just for the fun of it, but then don't slam on the brakes immediately after. They coast or level off and continue traveling. So I only see caps helping if someone repeatedly slams the throttle and then slams the brakes, which is basically racing, and not what the Tesla is made for.

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Tim

Absolutely. But the drop in efficiency is marginal. When I say marginal, I mean a drop in motor efficiency from 95% to 85%. That's alot less than IC engines. Everything else you mention is the same regardless of whether you're driving steady state or accelerating or decelerating. So the total drop in efficiency could be on the order of 10% not 70%. That's the goal.

But, you're pretty much right about the last part as to when caps would help and I guess I just disagree with you. The roadster is a sports car. People are going to drive it exactly that way stoplight to stoplight - they aren't hypermiling, and they aren't timing stops to avoid using the brakes. In fact, I haven't seen one review of the Tesla where the driver drove it any other way, whether it was a magazine review or owner review.

vfx

Two things.

My wife is now quoting that number in the middle of my EV stump speech at parties. She is so proud of herself.

Chelsa said in a recent talk that all the engineers in Detroit know that number. They may not talk about Tesla much but they are paying attention.

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shark2k

You trying to make me feel bad I'm sorry that I am constantly reading about more than one thing at a time and can't memorize a simple number

-Shark2k

vfx

Yes, Now you must give the Tesla Battery count as your address in WONJ.

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The world loves to be deceived.