Tesla Roadster uses Li-Ion Batteries

[Phaetos]

The new Tesla Roadster car uses a pack of Li-Ion 18650 batteries to run it, 6,831 of them to be exact. The article is in March issue of Car & Driver, I think. Weighs 700 pounds!!

 

[lasercrazy]

Wow, that must have one hell of a protection and charging circuit.

 

[Mr Happy]

I've known about the Tesla and its giant bundle of laptop batteries for some time, but not really thought about the potential dangers of venting with flame.

In light of this demonstration it would be a good plan not to crash the car

 

[VidPro]

I saw on some video the guys working with Banks and banks of 18650 or 22??? type of li-ion cells , for some electric cars, and they were Loosing banks of batteries, and blaming it on the manufacture of them. "i donno whatsAmatter with em, these dont charge any more, and these have no voltage, and these . . . "

i wanted to tell them , Ummm you have to keep your array BALANCED there, or its not gonna work. they had huge voltages, by seriesing many many parellel banks, and i dont think they knew squat about balancing the things, so they were just destroying thousands of dollers of batteries by series charging them, and overcharging and getting anode disconnects. i wanted to cry , there was enough there that they destroyed to run 2 lectric scooters, or 50 lights, or . . .

 

[theone]

It would be really funny to see someone to take out all cells and charge it one by one. 3,730 cells left to charge! w00t, maximize battery life. rofl

 

[2xTrinity]

In light of this demonstration it would be a good plan not to crash the car

That's not the worst of it. I was utterly taken aback to find out nearly all vehicles use as part of their design a highly volatile and explosive fluid, containing almost 100 times more energy than LiIon by weight. This so called "gasoline", when exposed to high temperatures, has also been known to violently vent with flame!


IMO for electric cars I believe the A123 chemistry, as used in the Killacycle, is MUCH better than standard LiIon chemistry. Energy density is lower, but I believe the ability of the A123 to handle deep cycling might more than make up for tha.t I know that for hybrid cars using NiMH cells, the manufacturers specify very shallow cycles, effectively only using half of the cells capacity in order to get cycle lives on the order of a hundred thousand (multiple cycles per day, every day, for decades).

A123s I believe don't have nearly as much of a "penalty" for deep cycling as LiIon, so in vehicle applications, they might have more "practical" capacity than LiIons, like 18650s. Not to mention there is no problem with them venting (much safer chemistry) and the LiFePO4 is MUCH better at delivering massive bursts of current, as would be needed for acceleration, than 18650s.

In the case of a Tesla, where all the energy comes from the battery, rather than cycles of assisting and regeneration, as in a hybrid car, the cycle depth will be entirely dependent on length of the drivers' commute. Someone who drives a very short commute will likely have a long pack life,m someone else who pushes the bounds of the driving range regularly will consequently have an extremely short pack life.

 

[Fallingwater]

At the present state of battery technology, I find the concept of an electric sports car inherently flawed.
Electric micro-vans, scooters and bikes sound like decent ideas, but those are mostly ok for people who drive a lot but only for relatively short distances.
A sports car eats by definition much more energy than a tiny commuter car. I don't see how anyone would want a sports car that drops dead after a few laps on the racetrack.
This is why I've been deeply unimpressed by the Tesla Roadster.

The Vectrix electric scooter, on the other hand, sounds nice... that is, until you look at the price tag and faint.

The best idea for electric vehicles so far seems to be a small used motorbike with a dead engine. Gut it thoroughly and replace the engine with a decent electric motor and four flooded lead acid batteries. A bit bulky, but any lithium-based technology is likely to cost twice as much.

 

[2xTrinity]

At the present state of battery technology, I find the concept of an electric sports car inherently flawed.
Electric micro-vans, scooters and bikes sound like decent ideas, but those are mostly ok for people who drive a lot but only for relatively short distances.
A sports car eats by definition much more energy than a tiny commuter car. I don't see how anyone would want a sports car that drops dead after a few laps on the racetrack.
This is why I've been deeply unimpressed by the Tesla Roadster.

I disagree. The Tesla isn't being promoted as a race car, but as a flashy commuter car that accelerates fast.

Unlike gasoline engine, with an electric motor there isn't really an efficiency penalty for accelerating fast -- the motor in the Tesla has a pretty flat efficiency curve at all outputs. Also, with motors, you don't lose any efficiency by having a motor capable of fast acceleration either, like you would by having a larger displacement engine. For fast acceleration, LiIon is really the only all-electric battery choice, because of the high power/weight ratio.

That said, I still believe hybrid vehicles, specifically a series-hybrid configuration with electric motors taking over the whole drivetrain, still make more sense. Diesel fuel or gasoline still has 100x the energy density of LiIon by weight. Someone should build a super-efficient, low displacement diesel generator (not constrained by things like sudden load changes, or high power output as requirements) and continuously recharge a li-ion/electric drivetrain.

If they're going to make a production vehcile out of it, IMO they should use custom "big" LiFeP04 cells, rather than laptop cells, to simplify balancing.

The best idea for electric vehicles so far seems to be a small used motorbike with a dead engine. Gut it thoroughly and replace the engine with a decent electric motor and four flooded lead acid batteries. A bit bulky, but any lithium-based technology is likely to cost twice as much.

Lead-acids are crippling though in terms of power/weight ratio. Create a LiIon system with equal power and energy, and you probably cut your entire vehicle's weight in half, or better (and consequently, you improve acceleration by as much). I still the LiFeP04 system using in drill-packs are better though -- as they not as "touchy" as laptop cells. They're also very capable of quick acceleration for vehicles (check out "killacycle" on google)

 

[Bones]

At the present state of battery technology, I find the concept of an electric sports car inherently flawed.
Electric micro-vans, scooters and bikes sound like decent ideas, but those are mostly ok for people who drive a lot but only for relatively short distances.
A sports car eats by definition much more energy than a tiny commuter car. I don't see how anyone would want a sports car that drops dead after a few laps on the racetrack.
This is why I've been deeply unimpressed by the Tesla Roadster.
...

Although I agree in principle, this type of project does tend to push boundaries hard and receive attention from a much broader spectrum than the more practical applications, so it may inspire new inventions and inovations, perhaps even by some that wouldn't otherwise have been paying attention.

It could certainly require deep pockets to maintain though, especially considering assertions like this one in a sidebar by spectrum.ieee.org:

Life span is the weak point. But because the Tesla lacks an engine, it isn't bound by the California emissions regulation requiring that a power train last for 10 years and 150 000 miles (240 000 km). The company expects the battery to lose up to 30 percent of its capacity after five years. If you then want to buy another battery, Tesla says only that its own cost for the battery pack lies "north of $20 000."

This entry in the Tesla Motors Blog entitled 'The Most Coddled Automotive Battery Ever' has some interesting insights into their technology.

 

[Fallingwater]

I disagree. The Tesla isn't being promoted as a race car, but as a flashy commuter car that accelerates fast.

Ok, I got the classification wrong, but the idea doesn't change. It's the concept of performance that is incompatible with the current battery technology.

With the energy density of even the best LiIon cells you have two options: 1) go fast, 2) go slow and actually get somewhere before your battery dies.

You *can* build superfast monstrosities such as the Killacycle, but things like the Tesla Roadster, meant for use on normal roads, can only be useful if you don't push them. And if you're not pushing them what's the point of having a fast car?

Unlike gasoline engine, with an electric motor there isn't really an efficiency penalty for accelerating fast -- the motor in the Tesla has a pretty flat efficiency curve at all outputs

There is a penalty for going fast with any vehicle, unless you've managed to find a way to defeat aerodynamic resistance.
Yes, you can accelerate fast up to 50mph and keep going at that speed, but spending €€€$$$ just to have that in an electric vehicle doesn't strike me as a wise idea.

Also, with motors, you don't lose any efficiency by having a motor capable of fast acceleration either, like you would by having a larger displacement engine

You do lose money though...

Lead-acids are crippling though in terms of power/weight ratio. Create a LiIon system with equal power and energy, and you probably cut your entire vehicle's weight in half, or better (and consequently, you improve acceleration by as much).

True, but at considerable expense.

 

[TorchBoy]

Diesel fuel or gasoline still has 100x the energy density of LiIon by weight.

Does that include the weight of the fuel tank? Hmmm... Wikipedia has the figures for petrol 44.4 MJ/kg and Li-ion up to 720 kJ/kg. I'll give you 62x the energy density, without the fuel tank. :nana: But the point is clear that there's a long way to go.

Seriously, it's an interesting thread. FallingWater, why not have something which will get you - maybe slowly - to where you want to go, and yet still be able to accelerate like a spaceship when you want it to? Not everyone will want that, but for those who do the Tesla is a great start. But it is only a start. I believe the future of the (American) car will be in Silicon Valley, not Detroit.

 

[SilverFox]

Hello Ian,

The future of the American car may be in China... Isn't that where the batteries are made?

Tom

 

[TorchBoy]

Nice.

 

[2xTrinity]

Does that include the weight of the fuel tank? Hmmm... Wikipedia has the figures for petrol 44.4 MJ/kg and Li-ion up to 720 kJ/kg. I'll give you 62x the energy density, without the fuel tank. :nana: But the point is clear that there's a long way to go.

The weight of the tank is at least somewhat offset by the fact that you consume the fuel as you go along -- meaning when it comes time to fill up, oyu're carrying less weight, with average being "half full". In the case of LiIon batteries, even when capacity is spent, you still have to lug them around

Sorry, I always have to have the last word

 

[Bones]

Hello Ian,

The future of the American car may be in China... Isn't that where the batteries are made?

Tom

There, and perhaps the coal fields for the generation of electricity?

It is by far the most abundant energy source readily available to America.

In fact, America has been characterized as the Saudi Arabia of coal, and according to this wiki, there is enough coal available worldwide to provide the entire planet with all of its energy for 57 years.

Surely, given the ever increasing energy imperatives, a way to burn it cleanly can be found in the not so distant future?

Considering that China and India are also sitting on vast reserves of coal, just imagine the effect this would have on the price of oil, and especially on the dicatatorships and kingdoms relying on their income from oil to pacify their people...

 

[Fallingwater]

FallingWater, why not have something which will get you - maybe slowly - to where you want to go, and yet still be able to accelerate like a spaceship when you want it to?

Hey, I'm not saying nobody should buy the darn thing. If you've got a ton of money burning a hole in your pocket then hey, be my guest.

But the Roadster is a car for the rich. $100k for the car, $20k+ every two/three years to replace the battery pack even if you haven't used it much, super-exotic parts and very specialized mechanics.

The main appeal of electric vehicles is their comparatively very low per-mile running price. You don't see many managers worrying about how many miles to the gallon their cars do - it's the people who'd rather like not to spend money on gas that want commuting vehicles that just need to be plugged in a common power outlet at night, don't cost a lot and sacrifice some energy density to have longer-lasting batteries.

The Tesla is an expensive toy. Interesting as it may be, I doubt it'll change anything for us common mortals regarding electric vehicles.

Make a small utility car with a decent battery and a nice bank of supercapacitors to make regenerative braking actually work, and make it so it doesn't cost an arm and a leg. Then people will be impressed.

 

[TorchBoy]

I don't mind you having the last word at all, 2xT. You have a lot of good things to say.

I suppose that by taking the initial energy content of the fuel and the instantaneous mass you could really get 100x - I hadn't thought of calculating it that way. However, if you take the instantaneous energy content as well, your ratio gets worse as your tank empties, since the mass of the tank is an overhead that doesn't decrease.

I easily found the weight of the space shuttle's external fuel tank, but not that of a car fuel tank, so I have no idea if I'd need more than two litres of petrol left in my tank to have a better energy-to-weight ratio than batteries. I did find this article which talks about unorthodox ways to save fuel.

 

[csshih]

oh, Tesla demo at our school today.. I found out they charge the batteries in clumps, and to 4.1 V :thumbsup:

the protection circuit is covered by a layer of epoxy to prevent shorts, too.