just-an-allusion

My question, of course, is "why batteries are needed at all?"

graham

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

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.

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Tim

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. :)

TEG

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

Tim

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.

Joseph

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.

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Tim

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.

dpeilow

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).

WarpedOne

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.

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