Re: Tesla Motors vehicle question

Rick Powell <rkpowell@xxxxxxxxx> wrote:

James Robinson <wasc...@xxxxxxx> wrote:

If you assume that the same amount of energy has to be put into the
batteries as is contained in 15 gallons of gasoline, with a feed at
440 volts, that would mean the cables would have to be able to handle
15,000 amps over the five minute period. That's about 75 times the
maximum current fed into a typical house (200 amps) these days.
Those would be some heavy wires.

Interesting. I'm not an EE and I haven't done the calc's, but I think
the equivalent energy they were talking about was 2-3 gallons of gas,

That is exactly the problem with many of the claims about electric
vehicles. By using such low numbers without qualfication, they lead the
casual reader to believe that they will be able to drive just like they
do now, with a similar-sized vehicle, with similar or better
performance, and with similar range, all using much lower cost
electricity. All they need to do is plug their vehicle into a regular
wall socket in their garage each night, and they will be able to enjoy
low-cost driving without being tied to OPEC price spikes.

The reality of battery life and replacement cost, limited range, long
charge times, the need for specialized charging systems being added to a
house, poor cold weather performance, lack of electrical network
capacity, the likelihood of highway taxes being applied to electricity,
and so on are either glossed over or not mentioned at all.

Electric vehicles certainly have a place, and people need to clearly
know what the details of their cost and limitations are to make a
reasonable decision about acquiring them, or advocating the expansion of
their use.

One of the realities is that gasoline provides a large amount of energy
in a small package. Knowing that a typical vehicle requires 15 or more
gallons in a tank for the use we expect to get from it today provides a
good benchmark for evaluating the claims being made about electric
vehicles. If a similar amount of power in watt-hours isn't being
provided by the batteries, then you have to be suspicions that it would
be an apples/oranges comparison, and understand that any claimed savings
or benefits are likely accompanied by sacrificing something, or that
something has been left out of the glowing description.

I have read about the "supercapacitor" technology, which would solve
some of the battery issues, but AFAIK no one (such as "Eestor" or
other developers) has produced a working model with enough juice
storage to run a decent-sized EV.

Supercaps have good and bad things about them. The good things are that
they have very high efficiency in comparison to a chemical battery. That
really improves the overall efficiency of a vehicle. They also have
virtually unlimited life, meaning the whole issue of steadily declining
battery efficiency over its lifetime is eliminated, not to mention the
need and cost of regular replacement. In many ways, they seem to good to
be true.

There are a couple of bad things. At the moment, the physical size and
weight of a supercap or ultracap is about ten times that of a battery of
similar capacity. That pretty well makes them impractical for any use
where small size and light weight are important, such as for powering an
automobile.

Yes, EEstor is claiming to have surmounted that problem, and have
supposedly come up with a design that makes them smaller than equivalent
batteries, but they have yet to provide such a product for public
scrutiny. There are many physicists who, while trying to keep their
minds open, believe that a supercap that meets all their claims is
impossible. It's just too big a jump to believe that an order of
magnitude reduction in size and weight can be so easily made.

There were somewhat similar claims made about lithium battery technology
by a couple of companies, but they ultimately proved to be overoptimistic
boasting. We will see, as EEstor has promised delivery of a working
battery by the end of the year. Not too many days to go.

The other issue with supercaps is that they have very low internal
resistance. What that means is that with a supercap of the capacity
needed to power an automobile, if there is a problem with wiring or some
internal short, it will result in a huge amount of current flow. As a
minimum it will instantly arc weld or melt anything in the short circuit
path. At worst, if the voltages are high, there will be a blinding
flash, and the possibility of major injury. The application of supercaps
will require careful attention to the safety of the circuits, and will
likely result in some nasty incidents.
.

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