More on the Tesla electric car

[imoldernu]

Maybe off topic, but definitely "electric car"...

While the article is long, you might find it interesting.

How China's Electric Car Dreams Became A PR Nightmare In America

[Chuckanut]

I have a question for the engineers in the group.

Speculation is that with the Tesla 'D' , the D stands for distance.

I have no idea if the speculation is right or wrong.

What I am wondering is if the battery pack can be tweaked to increase driving range at, maybe, the expense of acceleration. Just a thought since some people might rather have another 50 miles of driving range in place of a second or two added to the 0-60 time.

[ls99]

It already exists in software. Between the driver's ears and the hardware connection to the right foot.

[ERD50]

Quote:

Originally Posted by Chuckanut ... What I am wondering is if the battery pack can be tweaked to increase driving range at, maybe, the expense of acceleration. Just a thought since some people might rather have another 50 miles of driving range in place of a second or two added to the 0-60 time.

It's a reasonable thing to think about it, but I doubt it. From what I know, there are two ways they could trade off some of the acceleration for extended range:

1) A different battery chemistry - basically, when they designed it for 200 plus mile range, the batteries required for that range provide plenty of acceleration. Range is the limiting factor.

from wiki:

Quote:

The 85 kW·h Signature's ... accelerates from 0 to 60 miles per hour (0 to 97 km/h) in 5.4 seconds. ... the 60 kW·h base model' ... reaches 60 mph in 5.9 seconds The 60 kW·h battery was rated to deliver 230 miles (370 km), ... an 85 kW·h battery was rated at 320 miles

So very little difference in 0-60 times (13.5% delta), while the range is ~ 30% less. And for all we know, they limited the 0-60 for marketing purposes (less battery weight would help improve acceleration), to better differentiate and 'justify' the higher cost for 85 kWh batteries.

2) Use more of the batteries charge range (charge it a bit fuller, discharge it a bit more) - this would increase range, but hurt battery life longevity. But if they reduced the peak power it would deliver with the controller, that would help offset some of the loss of life.

-ERD50

[Zathras]

Looks like they did a little bit of both.
0 to 60 time is 3.2 seconds, for the very top end model.
Range went from 265 miles to 275 miles!

You got to love those electric motors

[Totoro]

You can't trade acceleration in for more distance at the battery level. Only thing you can do is accelerate less yourself and drive slower in general, that'll give you more mileage.

The reason why electric cars accelerate as fast as they do is that they get maximum power "instantly". This is in contrast with an internal combustion engine that has maximum power at a certain rpm.

So for more distance you need better (more energy-dense) batteries or larger batteries. Of course also at lower prices ..

[Zathras]

Quote:

Originally Posted by Totoro You can't trade acceleration in for more distance at the battery level. Only thing you can do is accelerate less yourself and drive slower in general, that'll give you more mileage. ...

Musk just did
Although until the EPA numbers are out we won't have a definitive answer.
A better example is the S85 rather than the P85.

The 85D has a range of 295 at a constant 65 mph. The RWD 85 has a range of 261 at a constant 65 mph.
Same battery, two motors, and most likely smaller motors. More range AND more acceleration.

[Ronstar]

A buddy's wife just got one. Given the cost of electricity in our area, he calculated that their Tesla is getting the equivalent of 38 miles per gallon. So far they really like their Tesla.


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[ERD50]

Quote:

Originally Posted by Zathras Quote: Originally Posted by Totoro You can't trade acceleration in for more distance at the battery level. ... Musk just did ...

Quote:

Looks like they did a little bit of both. 0 to 60 time is 3.2 seconds, for the very top end model. Range went from 265 miles to 275 miles!

No, I don't think so. I don't think these improvements came from trading acceleration for more distance at the battery level.

Four-wheel drive could allow better 0-60 times, assuming this was somewhat limited by wheel slip ( a pretty safe assumption at 'bat-outa-hell' acceleration ranges).

Not sure where the ~4% range improvement comes from. Two smaller motors might be marginally more efficient (I kinda doubt this would be much), or does driving 4 wheels add some small mechanical efficiency over two? Or maybe their new motors and controllers are just tweaked a little to squeeze a bit more out of them?

Plus, if their data on battery degradation is telling them their estimates were conservative, maybe they just decided to widen the charge-discharge points a tiny amount? Trading range for battery lifetime.

-ERD50

[Zathras]

Quote:

Originally Posted by Ronstar A buddy's wife just got one. Given the cost of electricity in our area, he calculated that their Tesla is getting the equivalent of 38 miles per gallon. So far they really like their Tesla. Sent from my iPad using Early Retirement Forum

Ouch!
Based on cost, I am getting around 135mpg. We are moving within a year and that will change to about 270mpg.

If they haven't already, I would suggest to your friend to check to see if their utility has an off peak or time of use billing rate.

Although 38mpg isn't bad I suppose. Much better than average.

[Zathras]

Quote:

Originally Posted by ERD50 No, I don't think so. I don't think these improvements came from trading acceleration for more distance at the battery level. Four-wheel drive could allow better 0-60 times, assuming this was somewhat limited by wheel slip ( a pretty safe assumption at 'bat-outa-hell' acceleration ranges). Not sure where the ~4% range improvement comes from. Two smaller motors might be marginally more efficient (I kinda doubt this would be much), or does driving 4 wheels add some small mechanical efficiency over two? Or maybe their new motors and controllers are just tweaked a little to squeeze a bit more out of them? Plus, if their data on battery degradation is telling them their estimates were conservative, maybe they just decided to widen the charge-discharge points a tiny amount? Trading range for battery lifetime. -ERD50

I stand corrected, that trade off can't be made at the battery level, just at the vehicle level.
Prior to this, I don't believe anyone has managed to increase both efficiency and performance in a vehicle.

One of the motors in the Performance model is a smaller motor and each is geared differently.
Because the electric motor is relatively small, the added weight is overcome by the efficiency.

The possibilities with EVs are much much greater than most people appreciate.
Here is a family sedan that has the performance of a McLaren supercar for a fraction of the cost (although still a ton of money).

Personally I am more enthused about the much larger range gain of the standard 85kWh AWD model available in February.

[Ronstar]

Quote:

Originally Posted by Zathras Ouch! Based on cost, I am getting around 135mpg. We are moving within a year and that will change to about 270mpg. If they haven't already, I would suggest to your friend to check to see if their utility has an off peak or time of use billing rate. Although 38mpg isn't bad I suppose. Much better than average.

Thanks for the info! I'll relay your message to him. I talked to him the day after they picked up the car, so the 38 mpg calculation was from their first charge, and probably not off-peak.


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[ERD50]

Quote:

Originally Posted by Zathras Ouch! Based on cost, I am getting around 135mpg. We are moving within a year and that will change to about 270mpg. If they haven't already, I would suggest to your friend to check to see if their utility has an off peak or time of use billing rate. Although 38mpg isn't bad I suppose. Much better than average.

Agreed, a 38 mpg 'fuel' cost equivalency doesn't sound right. Zathras, for clarity, could you break out your cost #'s? Your miles per kWh, your kWh cost, and gasoline $/G figure.

Related to that, what kind of phantom/vampire costs are you seeing now, after the software updates? Do you have a total power in for the car (IOW, is that charger socket metered separately, so you know the total kWh that were 'fed' to the car, not just what the car draws from the battery)?

Quote:

Originally Posted by Zathras ... Prior to this, I don't believe anyone has managed to increase both efficiency and performance in a vehicle. ...

I think your fascination with EVs and Musk is clouding your thinking. There's a long list of developments that do exactly that. Of course, any efficiency improvement can be weighted by the engineer - do we use this efficiency to improve mpg, total power available, or some of both?

Turbocharging, over-head valves, multi-stage carburetors, fuel injection, direct fuel injection, electronic ignition, multiple valves per cylinder, variable valve timing, variable displacement (shutting down some cylinders when not needed for acceleration), electronic engine controls, multi-weight oils, synthetic oils, .... to name a few.

Quote:

One of the motors in the Performance model is a smaller motor and each is geared differently. Because the electric motor is relatively small, the added weight is overcome by the efficiency.

Have you found any good technical links on this, I'd be interested to read more detail? I'm curious as to why the 2nd motor would be smaller and geared differently - I would think ~ 50/50 would be the best?

And generally, two smaller units would have poorer power/weight ratio than one large one - economy of scale almost always wins. So I'm curious about that as well.

Quote:

The possibilities with EVs are much much greater than most people appreciate.

I think it is just the opposite. I think many people (most? I don't know) think that EVs will develop along the lines of computers, but that is not the case. As we've discussed, motors and batteries are already ~ 90% efficient - there just isn't much meaningful improvement available there. Yes, they can be made smaller, lighter and cheaper - but they have a long way to go to reach an ICE or ICE/hybrid value for a more median buyer. ICE/Hybrid technology is not standing still either.

Quote:

Here is a family sedan that has the performance of a McLaren supercar for a fraction of the cost (although still a ton of money).

Yes, but the catch is 'still a ton of money' - and to get back to Chuckanut's question, you need that much battery capacity to get the range. If Tesla were to scale down the performance to more typical family sedan levels, they could save some $ with smaller motors and drive train, lower performance suspension and tires - but you would still need most of that battery pack to get that range, and therefore still a very $$$ vehicle.

But yes, compared to other performance vehicles, it's a pretty wild ride.

-ERD50

[Chuckanut]

FWIW, I notice that the Tesla website claims "No Tailpipe Emissions". I'm glad they don't claim the car has zero emissions like another brand does.

On the subject of the cost of electric fuel for the car, please remember that so far electric car owners do not pay the equivalent of a gasoline tax. That day is coming for certain. I see no reason that gasoline engine owners should subsidize the road for electric car owners - most of whom probably have above average incomes at this time.

That said, I admire the work of Mr. Musk and his crew in bringing electric vehicles to this level. They are doing some very interesting work to say the least. Finally, I would love to have a Tesla, any Tesla, parked in my garage.

[ERD50]

Was able to answer a few of my questions - this makes more sense to me now:

Tesla Model S P85D - Dual Motors, AWD, 691 hp, 3.2 seconds to 60 - Road & Track

Quote:

All three new models—the 60D, 85D, and P85D—use the same 188-hp front motor. The 60D and 85D use it on the rear axle as well. The supercar-grade P85D, however, keeps the existing 470-hp motor in back for a monstrous 691-hp / 687 lb-ft combo.

OK, so the 60D and 85D use two smaller, but equal sized motors. The 'no holds-barred' P(erformance)85D goes with the new, smaller motor in front, and the old larger one in back for max HP.

bold mine:

Quote:

Both the 60D and 85D shave two tenths off their acceleration and quarter-mile times and add 10 miles of range, the latter thanks to the additional regen capacity from the second motor.

Ahhh-hah! I never really thought of that, but most braking comes from the front wheels, and with a rear motor, they can't fully take advantage of regen. The second motor does that for them. Mystery solved!

-ERD50

[Totoro]

Quote:

Originally Posted by ERD50 I think it is just the opposite. I think many people (most? I don't know) think that EVs will develop along the lines of computers, but that is not the case. As we've discussed, motors and batteries are already ~ 90% efficient - there just isn't much meaningful improvement available there. Yes, they can be made smaller, lighter and cheaper - but they have a long way to go to reach an ICE or ICE/hybrid value for a more median buyer. ICE/Hybrid technology is not standing still either.

It seems we are roughly doubling the wh/kg every 8 years (although it seems to be going faster recently, more like 5 years). Not great, but gasoline has a fixed energy density (around 32 MJ/L), so batteries will eventually catch up in that dimension. Might take a while though, Li-Ion batteries currently are 2.5 MJ/L, that's a ~10x difference (or ~5x if you take the higher efficiency into account of electric).

Cost-wise same thing, there is an ongoing trend to cheaper batteries. Halving every 5 years or so seems about right.

So, all in all this means that by 2024 we'll have likely a battery widely available weighing the same as the ones now, only it goes twice the distance and costs half as much.

Not quite the pace we're used to with computers, but still amazing in my book.

But you are right: barring a short-term major breakthrough small, cheap compact cars will be self-driving before they become fully electric

The high-end gas-using heavy cars though will quickly meet their demise from 2020 onwards at this rate.

Sources:
Energy density - Wikipedia, the free encyclopedia
http://images.thecarconnection.com/l...00424516_l.jpg
http://onclimatechangepolicydotorg.f...nd-density.jpg

[Zathras]

So many points good points!

ERD, I m the furthest thing from mechanically inclined. My comment about not being aware of a company increasing both efficiency and performance was a general look at offerings on the market. If you want more performance, you get a V-8 instead of a V-6, but efficiency goes down. More efficiency, generally means engine size goes down, meaning performance suffers.
If you get an AWD version of a vehicle it may gain some performance, but tends to loose efficiency. Not so for electric.

Please forgive my ignorance of the technologies you mentioned, I'll take your word for it.

Costs: I use a 3miles/kWh for consumption, 6¢/kWh for my TOU costs. That gives me 50 kWh for $3.
Subtract 10% for charging losses to get 45kWh.
Multiply by 3 to get 135 miles for $3.

Next year our TOU overnight rate should be under 3¢, doubling our "mpg"

[ERD50]

Quote:

Originally Posted by Zathras So many points good points! ... My comment about not being aware of a company increasing both efficiency and performance was a general look at offerings on the market. If you want more performance, you get a V-8 instead of a V-6, but efficiency goes down. ...

Right - but in those cases you are mostly looking at just 'bigger' for more performance, not a real technology change to improve efficiency, which as I said, can be applied to mpg, performance, or a blend of the two.

All the things I listed, and many more are technology advancements. And I think we can call the dual-motor change by Tesla as a technological advancement, they are now making better use of regen. Or, another view would be that Tesla had a sub-optimal design, and just fixed it - which is probably more accurate, since it seems the majority of EV/hybrids that can use regen are already front-wheel drive.

Quote:

Costs: I use a 3miles/kWh for consumption, 6¢/kWh for my TOU costs. That gives me 50 kWh for $3. Subtract 10% for charging losses to get 45kWh. Multiply by 3 to get 135 miles for $3. Next year our TOU overnight rate should be under 3¢, doubling our "mpg"

Thanks, those are pretty low kWh rates. Yes, the previous 38 "mpg" numbers seem way out of line. Just goes to show, heh-heh, if you want economy you have to pay for it!

Quote:

Originally Posted by Totoro ... So, all in all this means that by 2024 we'll have likely a battery widely available weighing the same as the ones now, only it goes twice the distance and costs half as much. ...

Some of these may also be hitting diminishing returns? I tried doing some searching, too much stuff to sort through to find meaningful projections so far, I'll try again later.

As I've said earlier, if they could just increase the max instantaneous discharge rates faster than the other specs, that could be a big plus for hybrids and plug-in hybrids. Take the Chevy Volt, with ~ 40 mile range. If you doubled what you could draw short term (like for acceleration) from those batteries (all else being equal), you could remove half the batteries, and therefore lower the cost significantly, and gain some space. The electric-only range would be cut almost in half (batteries would be half the weight, so that helps range a bit), but that's not really a big deal with a 'range extended' hybrid. You'd still get the first 20 miles of all trips at the cheaper kWh 'fuel' rate, which is a significant % for many people.

That's why I think hybrids will be the dominant technology going forward for the next 15 years or more, I just don't think pure EVs are going to compete. As I said, ICE/hybrids aren't standing still, the ICE is inefficient enough that new materials and techniques might ring out considerable efficiency improvements, which is not the case with electric motors and batteries (being+90% already). There's also the potential for small turbines to replace the ICE - new materials are making these more competitive. Or some new development?

-ERD50

[Chuckanut]

Quote:

Originally Posted by ERD50 That's why I think hybrids will be the dominant technology going forward for the next 15 years or more, I just don't think pure EVs are going to compete.

I tend to agree. I just read a comparison of a number of small, fuel efficient autos that were not hybrids. The top ones got about 36 mpg, not bad. But..... my much larger and heavier mid size hybrid sedan gets about 40 mpg.

I won't even mention the near 50mpg Prius.

Full electric power makes the most sense in bigger, faster, heavier vehicles. That is where one sees the huge improvements in fuel economy when compared to peer vehicles near the same price. Tesla is smart to be in that market rather than trying to compete against a 50mpg $22,000 Prius.

[mpeirce]

What I'm very glad to see them add is the safety/semi-self drive systems. I didn't get why they didn't have those last year when I was shopping. Evidently, they just hadn't gotten it to work yet.

They are still playing catch up with Mercedes, BMW, and Audi. Each has a slightly different mix of semi-self driving systems. The only slight edge I see with the Tesla is the "engage the turn signal and it changes lanes by itself". My Mercedes makes me engage the turn signal, then actually turn the wheel enough to changes lanes, thereafter it reacquires the lane lines and then takes over again.

They mentioned they'd like it to park itself in the garage. Nice idea, though they either need inductive changing or some sort of self-plugging in system to get it to recharge in the garage. There is a nice video that Audi showed of a stock A6 (i.e. the existing sensor package) with custom software that allowed you to get out of your car and the car would park itself in a parking garage. Later it would come back to pick you up when requested.

I wonder if this stuff will be available on the model X - hope so.