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graham
Active Member
Cost of the materials, certainly - but for anything non-track related, possibly cost in re-crash testings. which is mega-expensive. Since (to our knowledge) they have not started crashing the Model S, there is still a chance for that. But I can't imagine them doing more design work on the Roadster in the near future.
Since there are lots of similarities between the Roadster and the Model S drive train (supposedly) it is possible they could pioneer it with the S and back-port it to the Roadster at some later date.
JRP3
Hyperactive Member
Is there any evidence that suggest a new round of crash tests for 200lbs or so of weight difference? There has to be some leeway in the testing, that could be the difference between 2 150lb people in the car and 2 250lb people.
I agree with you Graham, I have no idea what the crash test requirements would be to modify the ESS, but they could be potentially significant. I always assumed that the proposed "track changes" Elon mentioned probably were more a factor of a redesigned PEM that operated at a higher voltage and power to increase 0-60 times rather than a redesign of the battery. I think you're probably right that we won't see this until the next major redesign of the Tesla, but maybe we can see a track enabled mule to get a taste of the potential benefits.
Did you know that the Prius already has Ultracaps?
And the FCX has a bunch of them...
Toyota's winning ultracap race car
Using Ultracaps for power steering and regen braking
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You're all over this stuff TEG. Do you sleep? Now that I think about it, it makes sense for the FCX since fuel cell power density is really low, and they don't have any power surge ability of their own. Not to mention that they make ultracaps downright cheap in comparison.
I think AFS trinity also uses ultracaps in their PHEV conversion.
I think AFS trinity also uses ultracaps in their PHEV conversion.
Honda ditched ultra cap; the new FCX uses lithium-ion.
Also, the reason given in the forum post about the Prius having ultacaps is that they needed a battery that could be charged very quickly.
The Prius has a relatively small battery pack along with the fact that NiMH can't handle high charge/discharge rates. I'd imagine it is because of these two reasons that the Prius needs ultracaps.
However, the Roadster's battery pack is relatively enormous and lithium handles high charge/discharge rates better than NiMH. For these reasons, the Roadster doesn't need ultracaps.
I've driven an ACP Ebox - it also has a battery pack of thousands of laptop cells like in the Roadster and, as far as I know, no ultracaps - and it has VERY strong regen. It'll bring the car to a stop very quickly at low speeds. You really don't want anymore regen that this car gives. However, this is only at lower speeds.
Ultracapitors probably would extend that strong regen capability to higher speeds. But the problem is that at high speeds you don't need to brake much because you're usually on the highway when you're at high speeds. And since you don't brake much on the highway, there's little opportunity to regen, which means the ultracapitors wouldn't need to be used very often.
The only possible benefit I see with ultracaps would be to assist in acceleration, possibly reducing battery abuse and extending battery life. But I don't think the extra volume, weight, and cost are worth it since most EVs probably aren't going to be driven that hard.
Also, the reason given in the forum post about the Prius having ultacaps is that they needed a battery that could be charged very quickly.
The Prius has a relatively small battery pack along with the fact that NiMH can't handle high charge/discharge rates. I'd imagine it is because of these two reasons that the Prius needs ultracaps.
However, the Roadster's battery pack is relatively enormous and lithium handles high charge/discharge rates better than NiMH. For these reasons, the Roadster doesn't need ultracaps.
I've driven an ACP Ebox - it also has a battery pack of thousands of laptop cells like in the Roadster and, as far as I know, no ultracaps - and it has VERY strong regen. It'll bring the car to a stop very quickly at low speeds. You really don't want anymore regen that this car gives. However, this is only at lower speeds.
Ultracapitors probably would extend that strong regen capability to higher speeds. But the problem is that at high speeds you don't need to brake much because you're usually on the highway when you're at high speeds. And since you don't brake much on the highway, there's little opportunity to regen, which means the ultracapitors wouldn't need to be used very often.
The only possible benefit I see with ultracaps would be to assist in acceleration, possibly reducing battery abuse and extending battery life. But I don't think the extra volume, weight, and cost are worth it since most EVs probably aren't going to be driven that hard.
Joseph
Good points all. I agree with pretty much everything you say, except to argue that the Roadster isn't meant to be compete with most cars. Its supposed to be an electric Ferrari, and as such, its unlikely that you can expect drivers to drive it like a Prius. The cost would be prohibitive and not worth the effort on even the whitestar, but as an optional package to the roadster, the cost would only be marginal to the already high cost. I guess it just irks me, because I know that this is one area where the Tesla should excel at since an electric powertrain is not inherently less efficient when driven like Top Gear did than when you drive it like a Prius. Its just a design issue. Which is a huge differentiator between BEVs and IC cars.
Good points all. I agree with pretty much everything you say, except to argue that the Roadster isn't meant to be compete with most cars. Its supposed to be an electric Ferrari, and as such, its unlikely that you can expect drivers to drive it like a Prius. The cost would be prohibitive and not worth the effort on even the whitestar, but as an optional package to the roadster, the cost would only be marginal to the already high cost. I guess it just irks me, because I know that this is one area where the Tesla should excel at since an electric powertrain is not inherently less efficient when driven like Top Gear did than when you drive it like a Prius. Its just a design issue. Which is a huge differentiator between BEVs and IC cars.
That was Malcolm - I was saying that by sticking to the same ESS box they could probably avoid crash testing. (i.e. do other manufacturers test every ICE size? Probably not).
This is a very popular misconception that regen is limited by what batteries can absorb.
Is is not. Regen is NOT limited by batteries.
Current roadster has rearwheel-drive which also mean it has only rearwheel-regen. Strong regen equals strong braking. You do not want strong rearwheel only braking, especially on the track because it just destroys the stability and rear traction.
Motor has enough torque to spin the wheels which means it has enough torque to block the rear wheels under maxpower regen. Such a situatuon equals disaster.
Capacitors are not weightless so that wheight would be much better spent on some additional batteries.
JRP3
Hyperactive Member
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.
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).
JRP3
Hyperactive Member
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.
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
Hyperactive Member
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.
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.
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.
shark2k
Member
:smile:
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.
You trying to make me feel bad :frown: I'm sorry that I am constantly reading about more than one thing at a time and can't memorize a simple number :tongue:
-Shark2k
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