OT More on electric cars

[Chris Hogg]

An interesting three-part discussion on the merits of electric vehicles:

[Jeff Layman]

There are a lot of interesting points, but I still have concerns about charging capacity, both for the generating network to supply it when we all have electric cars, and for the wiring involved.

Some of the comments at the end of Part 3 are interesting. One in particular is worth repeating as a practical constraint to fast charging:

"VOLTAGE kills. AMPERAGE requires copper. WATTAGE is Volts times amps. I?m trying to imagine a world where 500 kW can be ?pumped? over a 3 meter charging cable that?s long-term safe, using cable that is light enough to be handled by my fiancé, and has an exactly ZERO chance of accidentally electrocuting the operator in the middle of a rainstorm, with wind, in the dark, near the sea.

There is a reason why 400 volts is considered the top limit to industrial use for staff without special training and permits. It, just like 240, 220,120 and so on can kill you, but with way less ability to percolate thru invisible cracks in insulation, or with the nominal conductivity of flying rain water.

500 kW at 400 volts (if we stick to the safe voltage) requires 1,200 amps. On 2 wires AC or DC. Or 800 amps on 3 wires, if AC. Power loss (cable heating) is ?ohmic?. E=IR ? P=IE ? P=I²R = E²/R. Cable heating in turn depends on power loss and thermal wicking. If a cable is actively cooled (having either a hollow center or jacket with flowing non-ionic coolant), the power loss can be quite high. High power loss is high resistance, which is minimal copper, which is light weight. But if you want durable, ?10 year? outdoor flexible cables, power loss must be low, because insulation is thick, heat conductivity, low.

My fiancé won?t be able to man-handle a 35 lb, 10 foot power cable. Period. yet, this is exactly what 1,200 amps (x 2) or 800 amps (x 3) conductor cable would require, for passively cooled cable that can work up to Las Vegas ambient heat levels.

Moreover, tho? the ?easy solution? is just to raise the voltage (to 600 or 800 or 1,000 volts), this in turn puts rather outrageous safety requirements on the whole under-the-hood car battery and energy management subsystem. And it becomes exponentially harder to make a

10-year-safe outdoor power cable.

While I don?t doubt that there are 300 and 500 kW constant-current-source chargers now envisioned, they?re also in the realm of having 10 gallon-per-minute gasoline pumps. Over-filling becomes a life-and-limb threatening petrol-gusher problem, when ANY component goes awry. Its one of the reasons (at least in USA) why conventional pumps are limited to 4?5 GPM. ?Fast enough?. Only the Big Truck diesel stations get away with 10 GPM. And only those on Big Highways. "

[tim...]

Yup

me to

He justifies the viability of electric cars for the times when you need to do the long distance trip on the premise that they can (or will in future) be fast charged when you stop for your toilet break.

well in order not to have to join the queue of 50 other people all stopped for their toilet break that would mean that every single parking place at the motorway services will have to have a charge point

so

1) how is that additional cost going to be paid for

2) where the heck is that all that concentrated power requirement going to come from?

tim

[The Natural Philosopher]

reasonable point, but one that is solvable by sane engineering I think Liek a replaceable standard sized battery that simply gets swapped out at a service station.

The paradigm has to change for electric cars, and the direction it changes in is not fully established

[The Natural Philosopher]

by charging the motorist more for a motorway fast charge.

A fuckoff substation.

Same as the railways have already.

[alan_m]

So you replace your nice new battery with one abused by someone else or one at the near end of its life cycle and you no longer get the performance/range expected?

[Dave Plowman (News)]

The sort of idea promoted by one with their head in the clouds.

A battery pack is by far the most expensive part of the car. And likely to remain so. With also a finite life.

So you change your fooked one for a good one for the cost of the electricity. Or even more likely get given one which will just take you down the road before failing.

And it hardly sits nicely in with one who wants to 'bring back control' It would require compulsory cooperation between car makers world wide.

[Roger Hayter]

This can only work if you purchase about half the value of the car and lease the battery from the manufacterer, seller, or specific leasing company. Then what you are leasing is access to a workable battery, the leasing company being responsible for old or failed batteries.

The biggest problem with this scenario is the waste of space and weight involved in making the battery a separate module rather than using all the nooks and crannies in the car structure to place battery cells.

[tim...]

been discussed many times as a solution

don't think it's a goer

tim

[The Natural Philosopher]

Or somewhat vice versa. The charging stations will know

And it never is 'your nice new battery' It's merely '150kWh' sold to you in a reusable casing...

>

[The Natural Philosopher]

Yes. That is how I see things working people today dont actually LIKE owning things that need serviceing. They just want the use of them.

You would never do that anyway.

The battery needs to be modular, cooled and slung at the lowest point of the car - in fact it is what sits between the wheels under the floor.

[Jeff Layman]

That's dealt with later in the comments thread by the same guy who wrote the comment about 500kW charging issues:

"Only battery swap tech can beat the 15 minute-to-charge barrier reasonably safely. And only that can be done thru robotics. And ?20 minute charge?, is full of a canard?s feathers: 80% of how many kilowatt hours? Oh? it depends. A very light-weight car, getting way better than

1 mile per megajoule (i.e. 5+ mi/kWh) and having ?only? a 200 mile range battery will have 40 kWh battery of which 80% is 32 kWh. Divide by ? hour (20 min) and you get 96 kW charge rate.

See, that?s doable. Already in service, actually, at some specialized SuperCharge Tesla stations. 72 kW is more typical though. (30 min charge). But oh? only Tesla may use Tesla supercharge stations. Monopoly.

But what of a nice premium car ? 400 mi range for non-stop convenience. Necessarily (today at least) heavy due to the extra-large battery. And all the supporting struts and so on to keep everything aloft. A 2,000 kg car, empty. Its mileage is closer to 3 mi/kWh. 400 ÷ 3 = 133 kWh battery. 80% is 106 kWh. This baby requires 1.5 hours of charge at a 70 kW SuperCharge station to fill up.

Thats not 20 minutes. More like 90."

[Roger Hayter]

Well I was speaking loosely. But I hear that the battery in a Tesla, for instance, is hardly modular in the sense that the labour costs of replacing it are high enough to make a car with a failed battery virtually valueless out of warranty.

[Theo]

In a Tesla, the battery /is/ the floor. See the picture in the article. (obviously there's a framing structure too, but the 'skateboard' battery takes up the entire space between all four wheels). The best way to swap that is to get out of one car and into another.

It's like an electric drill. All it is, at the most basic level, is a battery and some motors, plus a bit of plastic trim to make it comfortable. When the battery in your drill goes, that's more than half the value gone.

It's still a bit early to say, but it seems that the cooling and the charge management means the lifetime is a lot longer than you typically get out of laptop or drill batteries (that get hot and abused).

That said, used Tesla batteries are actually not terribly priced. A Model S module from a scrap vehicle is about 800 pounds on ebay for a 5.3kWh,

24V pack (weighs 55kg, there are 14 in the full skateboard). That will probably come down as more vehicles have accidents and end up in scrapyards. There are DIYers with software that talks to the charge manager and plumbing to plug into the liquid cooling circuit.

Just think, what could you make with a 5kWh battery pack...?

Theo

[Theo]

That's 'just engineering'.

Simply have a robotic arm that comes out of the charging station and mates with a connector on the car. The power isn't enabled until the computers at both ends have synced and negotiated charging capability.

It doesn't need to go in the side of the car like a fuel filler - for instance it could come up from beneath the car so there's no risk of coming into contact with humans, either mechanically or electrically. The arm could also carry its own cooling capability, and sufficient clearances would allow for the use of higher voltages.

There's no reason why car charging needs to look like a 1920s filling station...

(This would be for fast charging. For overnight charging the manual plug on a wire is cheap and probably good enough)

Theo

[harry]

? over a 3

?? P=I²R = E²/R. Cable heating in

ss must be low,

cable.

se the voltage (to 600

?. Only the Big

I have had an electric car for five years. The article is about right except most cars have a battery of 16 to 25 Kwh capacity not 75Kwh.

[The Natural Philosopher]

Tesla is virtually worthless as soon as its turned a wheel.

[Tim+]

Interesting stuff. Thanks for sharing.

Tim

[Steve Walker]

But Tesla also recently patented ideas about a removeable, battery replacement system didn't they? Unfortunately, they seem to be looking at a 15 minute swap by a combination of a machine and technicians - rather far away from their abandoned idea of a 90 second, automated swap.

SteveW

[Andy Burns]

All Teslas (up to the Model S at least, don't know about the Model 3) were designed to allow a battery swap, and the ability to do it in a couple of minutes has been demonstrated (video somewhere) but they've now chosen not to provide battery swaps as a service.