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Tesla’s promises don’t compute with current physics and economics of batteries

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Re: Tesla’s promises don’t compute with current physics and economics of batteries

#111

Post by baddox »

petre wrote: post #109
baddox wrote: post #96

Earlier quoted context omitted.

Interesting. I did not know that. I always figured they must need to manage heat, at the bare minimum by preventing huge draw for extended periods of time. Do you know where they radiate the heat, given that most Teslas don’t (to my eyes) have visible grill vents?

You only need to do that when charging the battery.

Oh, do the batteries not heat up when discharging quickly as well? I know next to nothing about battery chemistry, but for some reason I just intuitively assumed they did. RC aircraft batteries can certainly catch fire if something causes them to discharge extremely quickly.

Re: Tesla’s promises don’t compute with current physics and economics of batteries

#112

Post by avar »

nimos wrote: post #30

The Tesla superchargers currently charge at around 2% a minute up until about 80% which is 40 minutes to hit 80%. Tesla is advertising 400 miles in 30 minutes which is 80% of the 500 mile capacity. What is so hard to believe about a 33% improvement over a couple year old tech that is a couple years from release? Here are current industrial/transportation/residential electric prices in US [0]. They think Tesla will pa…

They don't even need the 33% improvement. They could just add that much battery and fake the charge rate by misinforming the user about the charge rate. I.e. say it took 30 minutes to get from 0% to 80%, but really you went from 30% to 80%, the car just shuts down at 30%.

They already have firmware unlocked battery capacity in their currently shipping cars, so this isn't some wild conjuncture. The margins on these vehicles are huge, they can just decide they'd like to pay for marketing by cutting into some of those and shipping more batteries with each vehicle.

Re: Tesla’s promises don’t compute with current physics and economics of batteries

#113

Post by dreamcompiler »

nbanks wrote: post #76
dreamcompiler wrote: post #67

Earlier quoted context omitted.

> He's basically working to replace Big Oil with Big Lithium. Electric cars need X kg of elemental lithium over the lifetime of the car. ICE cars need [on the order of] X kg of gasoline every 200 miles. This makes such a huge quantitative difference that comparing lithium mining to oil mining is almost pointless. In addition, lithium can in principle be recycled when the battery wears out. Gasoline cannot be recycled…

Some CO2 hydrogenation processes can produce liquid fuels which is kind of like recycling gasoline, but this is much more complicated than recycling batteries. It may still prove useful for fueling rockets or aircraft in a CO2 neutral way.

Understood. My former employer was researching this. But taking the separated atoms of gasoline and rebuilding hydrocarbon molecules from them is -- as you say -- not quite the same thing as recycling. And it requires very large energy inputs. It only really makes sense for aircraft fuel, since large or high-performance aircraft cannot (yet) be powered by batteries.

Re: Tesla’s promises don’t compute with current physics and economics of batteries

#115

Post by petre »

baddox wrote: post #111
petre wrote: post #109

Earlier quoted context omitted.

You only need to do that when charging the battery.

Oh, do the batteries not heat up when discharging quickly as well? I know next to nothing about battery chemistry, but for some reason I just intuitively assumed they did. RC aircraft batteries can certainly catch fire if something causes them to discharge extremely quickly.

They discharge slowly during driving, unless you floor the acceleration while driving up a slope, but I'm sure there are some kind of limits in place, to prevent the user from draining an unsafe amount of power from the battery.

Re: Tesla’s promises don’t compute with current physics and economics of batteries

#116

Post by ryanwaggoner »

koonsolo wrote: post #102
puranjay wrote: post #98

Earlier quoted context omitted.

I'm just constantly surprised and exhausted at the kind of pessimism and cynicism on display in any Tesla thread. Even people who have no stake in the company or its competitors feel compelled to chime in just to say "it won't work!" I don't get it. For better or for worse, Tesla has made the idea of electric cars feasible to the mainstream. Surely, that can't be a bad thing. Why knock down the idea so aggressively?

I'm starting my own business myself, and I notice there are fundamentally 2 kinds of people. One are the risk takers. Who know risks are involved, but do it anyway, sometimes against all odds, because the payoff (in any form) is big or huge. The risk is worth it for them. Then you have the conservatives, who just don't want to fail. They take no risk, don't step out of their comfort zone, because they might fall down…

I tend to agree, although I think this is probably a spectrum, rather than binary. Or maybe a bimodal distribution? I think that people probably tend one way or another, but we all probably display both reactions in different areas of life, at different times, etc.

I also think the terms you used probably aren’t ideal, because they imply a political connection that might make people resistant to your premise. It reminds me of the maker vs taker thing.

I like to think of it as reasonable vs unreasonable, as in the George Bernard Shaw quote:

“The reasonable man adapts himself to the world: the unreasonable one persists in trying to adapt the world to himself. Therefore all progress depends on the unreasonable man.”

Re: Tesla’s promises don’t compute with current physics and economics of batteries

#117

Post by bpicolo »

xg15 wrote: post #108

> Musk’s claim that the truck will be able to accumulate 400 miles of charge in 30 minutes would allow the Semi to achieve the first true long-haul ranges in the industry. A driver might start the day with 500 miles of range, top off the battery at lunch, and be able to complete driving the U.S. legal limit of 11 hours in a day with range to spare. But doing so would require a charger unlike anything seen before. Stu…

Estimates for the weight of the battery put it at like 10,000-20,000 pounds, and it's a 120,000 dollar battery. Who's going to maintain a million-dollar battery stock? You'd need liability insurance and equipment out the ass to deal with batteries that large. That's not a procedure you'd easily get done in 30 minutes. Charging the dang thing is a way better model.

Re: Tesla’s promises don’t compute with current physics and economics of batteries

#118

Post by jsjohnst »

petre wrote: post #85
kumarvvr wrote: post #65

Earlier quoted context omitted.

No, capacity of the battery isn't what determines the wattage at which you can recharge. It's the physical power supply constraints. If I have a 250v, 25 kWh battery, I can charge it at 250 V, 100 Amps for 1 hour or at 250V, 1000 Amps for 6 minutes. What charging rate I select depends on the voltage and chemistry in the battery. Can the battery support charging at such a rate. The charging current rate is limited to…

What makes it confusing is that the charging rates are given as 10C, meaning 10% of nameplate capacity.

That’s wrong. 10C means 10x the nameplate capacity. If I have a battery that outputs 40Ah, 10C means I can give it a charging current of 400A.

Re: Tesla’s promises don’t compute with current physics and economics of batteries

#119

Post by jsjohnst »

kumarvvr wrote: post #65
cperciva wrote: post #55

Earlier quoted context omitted.

My point is that having a larger capacity battery automatically increases the wattage at which you can recharge. It's not like a gas tank where a 100L tank takes longer to refill than a 50L tank.

No, capacity of the battery isn't what determines the wattage at which you can recharge. It's the physical power supply constraints. If I have a 250v, 25 kWh battery, I can charge it at 250 V, 100 Amps for 1 hour or at 250V, 1000 Amps for 6 minutes. What charging rate I select depends on the voltage and chemistry in the battery. Can the battery support charging at such a rate. The charging current rate is limited to…

Here’s some napkin math based on a few assumptions.

Assumptions: The article is correct and it’s an 800KW battery pack for the semi. I’m also going to go with a conservative assumption and assume 2C charging rate for the battery pack. I’m also going to assume that the semi will have the ability to take in a 480V charging current because it simplifies wiring and is easier to get in an industrial capacity.

With those assumptions, you’ll need 1.6MW of power, something that can be easily delivered with less than eight 500MCM cables (roughly 1” copper cables including insulation that weigh about 2lb a foot and are still rather flexible). This seems in line with the charging port photos I’ve seen for the semi. Neither the cables or the power needs are that dramatic, there’s wind turbines that put out that much power individually along I-70 in Kansas for example where there is thousands of them.

Re: Tesla’s promises don’t compute with current physics and economics of batteries

#120

Post by killaken2000 »

koonsolo wrote: post #102
puranjay wrote: post #98

Earlier quoted context omitted.

I'm just constantly surprised and exhausted at the kind of pessimism and cynicism on display in any Tesla thread. Even people who have no stake in the company or its competitors feel compelled to chime in just to say "it won't work!" I don't get it. For better or for worse, Tesla has made the idea of electric cars feasible to the mainstream. Surely, that can't be a bad thing. Why knock down the idea so aggressively?

I'm starting my own business myself, and I notice there are fundamentally 2 kinds of people. One are the risk takers. Who know risks are involved, but do it anyway, sometimes against all odds, because the payoff (in any form) is big or huge. The risk is worth it for them. Then you have the conservatives, who just don't want to fail. They take no risk, don't step out of their comfort zone, because they might fall down…

I totally agree. The naysayers aren't convinced that my designs for an interstellar pogo stick are viable. They just don't get my vision. Sure, there are some specifics to iron out and maybe it won't work but at least I'm trying to change things.

Best of luck to you.

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