dpeilow

Does that mean other manufacturers have to crash test every variant of a model with different ICEs?

If so, then this may explain a non-move to higher battery capacities. There is a small, but tangible difference in cell weight, which would translate to a few kilos or tens of kilos over the entire battery.

malcolm

Ah no. I was thinking about a major ESS redesign to capitalise on higher energy density allowing weight reduction.

I suspect Tesla may be penalised because of the "new tech" angle. but that's a complete guess

dpeilow

Maybe they could just put the fewer cells at the bottom of the ESS box, but keep the same overall form factor (to allow retrofitting to existing cars). That ought to be allowable.

malcolm

Yes 2200mAh to 2900mAh is a 30% increase. Does that mean they could knock out 3 of the 11 "sheets" in the ESS?

graham

My prognostication on "when will Tesla possibly re-crash the Roadster?"

We know it won't happen for the 2009 or the 2010 models, currently slated for Spring and Fall this year.

The 2011 model is probably out as that will be all about bringing Model S to market.

*possibly* the 2012 model could get some love? That would be my guess as the earliest possible.

TEG

That is a rather critical value for EVs. Unlike a laptop with a more uniform current draw, a performance EV is prone to fits of high current discharge (based on the disposition of the driver's foot!).

Tesla may not pick cells with the highest storage capacity because testing could show that some of the lower energy density cells can handle abusive discharge better in the long run (e.g.: after 100,000 miles of 'spirited' driving).

malcolm

That's a thought; if higher energy density cells exist toward the fringes of what can be achieved with Li-ion chemistry, does it become increasingly harder to make them stress-resistant?

In other words, within li-ion, is there a ceiling on EV applications and some commodity cells will just never be suitable?

Tim

Which is why I support using a small cap bank(20-50lbs) to minimize this. I know GM tried to use Safts LiNiAlCO2 cells, but discarded them due to thermal problems at high discharge rates. However, the Tesla's battery pack has a much lower dischare rate than any Hybrid or Phev, so I think they'd work(just as well as the cobalt cells they now have) fine for the Tesla. Plus right now the max regen is 27Kw, which leaves alot on the table in terms of energy recapture and would be solved by a cap bank. The other nice thing about a cap bank is that it decouples motor performance from the battery to a large extent. Which means that Tesla can go about increasing the power of the PEM and motor without regard to high C discharge on the battery and the resulting Peukert losses and thermal management issues provided it resizes the cap bank accordingly.

But we probably won't see any of this until the next iteration of the Roadster. Did anyone else notice that the quoted energy of the ESS per Road and Track pdf is now up to 59kwh? That is higher than I've seen quoted in the past. Maybe they've already upgraded the cells.

TEG

Yeah, I offered that up as a suggestion long ago. I think the response was that it is a lot harder to deal with the larger voltage swings you get with caps compared to batteries, but who knows. It sounds like a good idea to buffer the batteries with ultracaps... Not just because of the high current draw but you could potentially use the caps for quick regen/accel/regen and take advantage of their high cycle life without cycling the batteries so much.

Tim

Its more engineering work to be sure, but its not a particularly difficult challenge. Boost buck converters aren't exactly new science. All AC drives use caps exactly this way and the converters for V/HZ control. As for cost, I looked at the Maxwell website and online prices, and it looks like the requisite number of ultracaps would cost about $2-3K per car(for full accel buffering, decel buffering would be less). Expensive, but given the benefits, not overly so, especially when considering the benefits. I'm pretty sure JB is aware of all this, and it was simply a cost/design issue, more akin to the mantra that the perfect is the enemy of the good. Still, this is a pretty low hanging fruit that would make for a MUCH better track car.