Electric cars are a pipe dream

I agree completely with your post. What my recent post have been (showing I think) is that the simple 16Kwh EV battery (std to get the full $7,500 credit) can not be recharged in 10 minutes AND that the battery swap recharge idea is DOA, for more than a few percent of the cars (because the current power generation and gird would need unafforadable expansion - to be about 5 times larger than the current electric power system)
Only a small percentage of cars using battery swap recharge is not viable because, there would often be no battery swap center near you when you needed it.

 

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A better comparison would be a station where instead of getting gas pumped into your tank, the station replaces your physical gas tank and engine. (Weights would be approximately equivalent.)

Right. But again, what if the new battery is crap and only gets you 20 miles before it dies? What do you do then?

 

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It requires the same field as charging at a lower rate. I've demonstrated sub-2-minute charges to 50% capacity on experimental LiFePO4 batteries. Cooling is definitely an issue, but if you can cool an internal combustion engine effectively you can cool a battery pack.

 

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Tell more specifically where I make a significant error.

I did not do what you seem here to be suggesting I did:

The 42C temperature rise I calculated (approximately) for 1462 cell battery pack was based on the fact the HEAT generation would, to first order, be 1462 times greater and the cooling area would be increased by only 4 sides which are times 39 times wider than the cell width or diameter and of the same height as the cell is tall. ("To first order" as it is more than that due to the internal heating of some cells, at least if not all, will have greater than 4.5C temperature rise. Those "hot cells" will make more heat than if they were colder.)

Yes that is what I did to calculate the 42C temperature rise.

I have always said with active INTERNAL cooling it would be possible to charge a 16Kwh battery pack. Your suggestion of aluminum tubes (or even plates) between the rows of cells would not be "adequate" cooling for "cell 19" the one in the middle cell of 39 in a row unless the plates were quite thick (and expensive). I.e. there must be a thermal gradient in the plate to cause the heat being generated in cell 19 to flow to the outer part of the plate. I.e. cell 19 will "run hot" while charging. This is a positive feed back system as when it is hot its efficiency drops and more heat is produced. It may not fail immediately in the first recharge, but will be damaged, so in subsequent cycle it does fail. One failed cell in a series string means the battery has failed.

The motors probably use something like 300V (to get power with out too much RI^2 losses) Thus with 1.5 volt per cell you have 200 in a string.

I am not trying to be exact by giving numbers, only to trying to make the problem clear. Again I will admit I am wrong if someone can run 100 ten-minute full charge cycles on an passively-cooled, compact 16Kwh battery, which if it uses aluminum plate as you suggested does not add more than 10% to the either the cost or the weight without destroying it.

 

No that is false. If you charge slowing enough simple diffusion (zero electric field) will keep the ions striking the electrodes at the rate require, but no one want to take days to recharge. Thus near the electrode an electric field is created to dive the ions of the electrolyte to the electrode. I.e. the ionic density far from the electrode surface is greater than near the surface - i.e. a concentration gradient exist if the ion delivery rate exceeds what diffusion can provide. (For ease of understanding I am speaking of the electrode which is collecting ions from the electrolyte - basically the same story is going on at the other electrode which is giving up ions to the electrolyte, but of course near it the ion concentration is greater than in the bulk electrolyte.)

Let's consider a simple numerical example: Assume the open circuit cell voltage is 1.5V but 2.0 volts is applied during charging. The 0.5V, often called the charging "over voltage", is dropped in the electrolyte to establish the field gradient that is delivering ions to the electrode at an acceptable rate for charging, but the price for this more rapid charging is the same current is dropping thru 0.5 volts as is doing the useful charging of the 1.5 volt chemical potential. Thus 25% of the charging energy is being converted into heat.

If you want to charge even faster, apply 2.5 volts to the cell when charging. This will nearly double the electric field gradients. ("Nearly" as the actual gradient achieved is less than doubled, as the "polarization" or "ion concentration depletion zone" near the electrode will be wider.) Thus the time required for full recharge with 2.5V applied will not be reduced by 50%, but a lesser amount, perhaps 1/3 less charging time required. More of the charging energy is now being converted into heat. I.e. 40% of the applied energy is just making heat, not stored chemical potential.

As you can probably understand there is a limit on how fast you can charge a battery and not destroy it by the production of internal heat. The internal heat production is increasing faster than the required charge time is being reduced. If it were not for this fact, universal to all batteries, you could recharge the battery in you lap top in about a minute as your 110V (or 220V) house power is adequate to supply the energy needed.

 

To solve overheating I would think moulding air/fluid channels into the batteries structure that run into the battery itself which coolant fluid or gas could be pumped through would solve it? Increasing surface area will allow more heat to escape.

 

Oh and still think the title is dead. I'm not a CAN'T man.

 

I heard that. I think I mentioned Tesla motors earlier. But if I didn't, well I just did.

Sure it's an expensive car, but not as much as other cars that people with money buy.

 

Yes something like that does work. I call that active cooling as it requires energy, but is only needed part of the time, not for example with over night recharge at your house, but it would be a desirable battery feature when making a long trip. I.e. when you stop for 45 minute lunch, you could quickly top up your battery in those 45 minutes or an hour, if the needed power is available.

The real problem is that EV are not likely, at least in the near future to economically attractive to many, and in car active cooling just adds to the cost. More public transporatation and less private car driving is how to cope with the certain rise in gasoline costs. Or if concerned with CO2 release switch to a solar energy fuel like sugar cane alcohol.

 

An electric motorcycle I saw has an electric fan to cool the batteries.

 

Why? In discharge mode cooling is usually not much of a problem or could easily be solved by ducted air flow.

 

You assumed cells packed right next to each other, and you assumed flat sides for the cells, but the cells are round and so you can't eliminate the rounded sides of the cells as an area for heat exchange if they aren't on the outside of the pack.

ie a pack looks like this: OOOO not like this [][][][].

Indeed, the cells aren't that big and so they don't have to be packed right next to each other and (they don't have to be mounted in one flat array) and thus by simple packaging in a method designed for cooling the cells during the recharge that is equal to the slight gain they get from the neighbor cells is all that is required to keep the cells within the range of single cell passive charging.

Now consider a set of round cells but with a small radiative divider between them: O

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, where the : represents small tubes that cool air is pumped through and those tubes are preforated such that the cold air supplied to the pack effectively removes significantly more heat then passive radiation and you've got a simple effective system for cooling the pack while charging.

Arthur

 

Couple of fans running off a conventional car battery?

Also going on a bus isn't my thing, never will be. . .

 

BEV's will most likely, at first, be commuter and shopping vehicles, which make up 80% of all car mileage. Most middle class families have more than one car, so what is wrong with having a small, short range, shopping/commuter electric car (or two), and a different, fuel operated family car?

In time (perhaps 20 years), when fuel is too expensive, total conversion to all electric cars may be possible. Within that 20 year time frame, we can imagine that the technical problems of rapid recharge, plus design of long range batteries, will be overcome for EV's. That time frame also permits the infrastructure changes that will be required.

 

Yeah, that's what I envisaged, couple of fans. Just needs a clever moulding, but very doable at not much extra cost.

 

I think this is getting closer to the reality we see unfolding.

 

Not in traffic.

 

I have a charger sitting on my lab bench that charges LiFePO4 batteries to 50% in under 2 minutes - and it uses a _lower_ potential (and thus a lower electric field strength measured electrode to electrode) than a standard LiFePO4 charger. (3.4 vs 3.6VPC)

 

Heating during discharge is a much bigger problem than heating during charge for most EV's, since they usually charge at a rate much less than 1C. However, discharges during acceleration can easily be 2-10C. The higher current means higher I2R losses.

 

I agree with your assessment.I think a fair amount of discussion focuses on today's EV & Infrastructure forgetting that the market should mature as time goes on,not to mention the change over from gas,oil combustion engine is a long drawn out affair.Look at the change from year 1900 to now,who back then could have imagined today's auto's and infrastructure?