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Questions
and Answers regarding Electric Vehicles
By
Frank Didik
Copyright
2005
All
rights reserved |
 |
This
is a revised and expanded article originally entitled "Driving
an Electric Car"
written
by Frank Didik in 1992, which itself was a revision of his 1988
article on the topic.
Since the early 1980's, I have designed and built about 20 solar,
electric and non gasoline powered vehicles. I am also the founder of
the Electric Car Owners Club (now known as the Electric Car Society).
The following is an answer to many common questions and addresses
some of the misconceptions that people have regarding electric cars
with respect to pollution, safety, pollution and economy issues.
Overview:
Electric cars are in many ways similar to gasoline powered cars. They
can be comfortable, reliable and handle well. Electric cars are very
quiet. So quiet that you can barely hear the motor run, even at top
speed. This silence can be a danger to pedestrians crossing the
street since pedestrians can not hear the car coming. An electric car
operator must be constantly aware of this problem while driving in
populated areas. Until recently, most electric cars fell into two
categories--cars converted from gasoline power, such as a VW or a
Chevy Chevette or tiny cars such as Citi-Car and CommutaCars from the
mid 1970's to the early 1980's. . In the case of the Citi-Car, the
normal range in the summer of about 40 miles and in the winter time
about 30 miles per charge. With intermittent charging throughout the
day, the range can be extended up to 70 miles per day. The average
driver drives an estimated 28 miles per day. Most electric cars today
have built in battery chargers and all that is required to recharge
is a long extension cord and plug into a regular 110 Volt home
outlet. It takes about 7 hours to fully recharge the batteries. It is
possible to greatly reduce the charging time by increasing the
charging voltage, however by doing this, the life of the batteries is
shortened. The Citi-Car uses eight special 6 volt "deep
cycle" batteries, which are also commonly known as marine
batteries. These batteries weigh more then normal car batteries and
are designed to endure up to 2000 charges. Under normal conditions,
this translates to about two years of use. A set of eight deep cycle
batteries can cost as little as $800. When the cost of replacing the
batteries and the cost to recharge the batteries are considered, the
cost to run a small electric car (non-hybrid) is about three times
more than a conventional economy gasoline car. Since
the cost of electricity tends to more or less follow the cost of
fuel, it is unlikely that this ratio will change in the future.
Electric cars are fun to have and drive, but you will not save money,
nor will you really help the environment.
Converting a car from gasoline to electric: It
is possible to convert any vehicle to electric, however the frame of
a convention car would have to be greatly strengthened in order to
sustain the weight of the batteries. I would have to say that the
vast majority of conversions, which I have seen would have seen,
would have to be considered almost unacceptable. In most cases, the
end result is too heavy, underpowered, very short range and low top
speed. From what I have observed, the person converting the vehicle
has a conventional gasoline powered car that has a bad motor or the
person has access to a smaller car at a very favorable price. After
removing the existing gasoline engine, the chases is strengthened and
a rather heavy (and expensive) load of batteries are installed, in
most cases in the trunk and under the rear seat of the vehicle. The
gasoline engine being replaced by a 10 to 20hp dc electric motor or
an ac motor with a power inverter. The result is a vehicle that is
now anywhere from 700lbs to 1500lbs (300kg to 600kg) heavier than the
original gasoline powered car, even taking into consideration the
removal of the heavy gasoline engine. In many cases, the original car
was only 2000lbs and is now 1/3 heavier. Since the original vehicle
was never designed for such a heavy weight, the stability and
handling are often adversely effected. Conversions often seem to have
a range of 25 to 40 miles and a top speed of 50mph. These dismal
figures are rarely exceeded ... from what I have observed. Sadly, I
have noticed many exaggerated claims in the press, regarding top sped
and range. Prior to converting the vehicle, most people had expected
far greater performance. Another factor in home conversions is that
the projects are often not completed, since the person converting
either loses interest or runs into minor technical problems or can
not find specific parts. I have seen a wide variety of conversions
including a Porsche 914, Saab, fiat 850, Chevrolet Vans, Renault
LeCars (R5), VW Beatles and VW buses. Perhaps surprisingly, the most
successful conversions seem to be the VW bus. I think that the reason
is that the frame is relatively strong to begin with, so that the
batteries have a relatively good base and the VW bus is a rather
light weight vehicle.
Cost of operating an electric vehicle (non-hybrid):
On average, a straight electric (non-hybrid) car, which uses standard
deep cycle lead acid marine type batteries and is charged from the
mains, costs about 3 times more to run than a conventional gasoline
car. From a financial point of view, a diesel car, running on
something like filtered, used vegetable oil, such as the discarded
oil from restaurants, might be a better solution, however, the effort
in doing the conversion and in acquiring the used oil might not be
worth the effort. Perhaps buying an economy car such as a Ford Aspire
(43mpg), Honda Civic or one of the hybrids, such as the Toyota Prius,
might also be a solution. If gasoline should ever become difficult to
obtain (which, for the moment, seems unlikely), it may be possible to
use an electric car charged from such local sources as wind power, or
less likely, because of the high price of solar cells, solar power.
Do electric vehicles pollute?:
Electric vehicles do pollute, though most of the pollution is at the
point of electric generation. Though
the electric car itself does not burn fuel, most power plants use
"fossil" fuels to generate electricity, so we must consider
the pollution created at the power plant. Another issue that is
rarely addressed is the fact that most electric cars use batteries
which themselves have the potential to pollute if they are not
disposed of correctly. In many cases, batteries, while they are being
charged, gives off gasses, which can vary depending upon the type of
battery. This can be hydrogen and oxygen or sulfur fumes or other
gases. Hydrogen and Oxygen themselves are not considered pollution of
course, however the mixture can be explosive if they are allowed to
reform water. Another type of pollution that may be of concern is the
electro-magnetic emissions that some people feel can cause various
human ailments. Electric motors can be shielded with special alloys,
such as a highly tempered copper/nickel alloy, creating a type of Faraday
cage,
however this adds weight to the vehicle and it is not conclusive that
all emissions can be contained.
WHAT
ABOUT SOLAR POWER? With
current technology, it is not possible to effectively run a car
directly from the sun. So-called solar powered cars are in reality
solar charging battery powered cars. The sun is used to charge the
batteries. Nevertheless, there have been remarkable developments in
the area of solar cells and in the development of ultra light weight
solar charging battery powered cars. For example, the GM Sunraycer,
weighs 390 lbs, is 3.3 feet high, 6.6 feet wide and 19.7 feet long
and averaged 41.6 miles per hour over a total of 44.9 driving hours.
The GM Sunraycer is considered one of the most advanced
"solar" cars in the world and in 1987 won the Solar
Challenge race in Australia--a 1,950 mile race. Other solar cars have
attained speeds of over 110 mile per hour.
Are Electric vehicles safe?:
These days, some people are concerned with the electromagnetic
emissions of cell phones. It should be pointed out that the
electromagnetic emissions emitted from an electric car is many times
greater than that of a cell phone. Please
also refer to the paragraph above entitled "Do Electric
Vehicles Pollute?". There are many different types and sizes of
electric cars. Most electric cars are much heavier then they look,
due mostly to the weight of the batteries. The Citi-Car for example,
weighs about 1600 lbs. Since most electric cars are limited
production cars, they are built the same way as most racing
cars--with tubular steel frames. As a result, most electric cars are
structurally very strong--stronger then most conventionally produced
gasoline cars!
Acceleration:
An electric motor has what is known as continuous torque and therefor
has almost the same horsepower at any speed, though an electric motor
is more efficient at high rotational speeds. For this reason, an
electric car normally has better acceleration from standstill of then
the acceleration of a gasoline powered car! The Citi-Car can out
accelerate most cars from 0 to 20 miles per hour. The top speed of
the Citi-Car is however only 40 miles per hour.
What kind of DC motors you use? To
save weight, I use low HP (horse power) motors, usually between 3
and 6HP to power a car that has a total weight of 1800pounds
(including batteries). This is enough power to move the vehicle
between 35 and 55 miles per hour. This means that the car weighs
about 800kg and can travel between 50km and 90km per hour. A normal
small gasoline car, such as the old (1972) VW 1300cc Beatle has about
18hp and can travel up to 110km hour. An electric motor has
continuous torque and has different properties than a gasoline
engine. At 100km per hour, a normal car weighing 1000kg, only needs
to have a 7hp motor to keep going at 100km an hour. The problem is
acceleration and the time it takes to go 100km per hour.
What is the average speed that
can be reached with such a motor?
See above.
Should I use 4 separate motors (1
for every wheel) to get the best in performance or would it be better
to use 1 in the front and 1 in the back of the car and linking the
two together? This system of using motors in every
wheel was first used over 100 years ago. The problem with this setup
is that it is difficult to keep each wheel at an exact constant
speed. It leads to an instable car, in most cases.
Can I recharge the batteries by placing a
generator or an alternator on the electric motor, so that I can drive indefinitely?
No. This setup will not work since there is a concept of
conservation of energy and therefore, it would take the same (or
more) energy to recharge the batteries, thus the car would not move.
This is also known as perpetual motion and is contrary to the know
and established laws of physics. It should be noted however, that
while braking the car, you can slow it down by converting the forward
motion of the car into electricity that can be redirected to the
batteries. This is known as regenerative braking. From my
perspective, the added weight and complexity of the regenerative
braking system, plus the low absorption efficiency rate of
conventional batteries, ultimately provides for little if any gain in
range for the vehicle. In the case of long range driving, with little
braking required, the added weight of the regenerative braking
system, probably reduces range somewhat.
How many batteries will I need to run a small
two person electric vehicle? In general, to run a small
electric vehicle, weighing 700lbs, without batteries, you will
probably use between 8 and 10 6 volt batteries for a combined voltage
would be from 48 to 60 or more volts.
More about batteries including the time
consuming issues regarding charging: If you are using
conventional 6 or 12 volt "deep cycle" batteries, the
charging time will be about 8 hours per day. Once a week, it will be
necessary to take the caps off of all of the cells and top the cells
off with distilled water and then charge the batteries for 12 hours.
If one cell in the battery array is bad, it is important to replace
the battery immediately, since that one cell with drain the charge
from the entire battery array. Lead acid batteries have what is
referred to as a memory. This is a very inconvenient phenomenon
whereby if you re-charge the batteries before they are fully
discharged, over time, the batteries will remember that point and
this will actually reduce the amount of electricity that can be
stored in the battery. If your battery pack, when fully charged, is
able to let you drive 40 miles and you drive 30 miles to a particular
location, it is possible to charge the batteries for an hour or two
and then have the necessary power to go the additional 20 miles to
complete your 60 mile round trip. The problems that arise in this
case again, is the memory issue. As mentioned above, a fully
discharged set of batteries requires 7 to 8 hours of charging, but it
is interesting to note that within two to three hours, the batteries
are charged to an 80% level. This means that most charging occurs in
the first few hours. Again, however, if you charge your batteries for
only a few hours, the batteries will be greatly effected by the
memory issue and will rapidly decline in overall output.
Should I use a gearbox, if I build an electric car?
Hard to say, though most car companies use gear boxes. Perhaps a
bicycle transmission or a transmission from an old DAF car would be a
good idea. You may also be able to adapt standard machine tool
components that have variable speed Vbelt adjusters. For optimum
efficiency, it is better for an electric motor to spin at a higher
rpm (revolutions per minute) so that gearing, when starting from a
standstill, can measurably increase performance and duration. In the
case of a gasoline engine, the opposite is true, in that for maximum
mpg (miles per gallon), it is important to keep the engine running at
a relatively low rpm.
Should I use an electronic voltage control
system or an electro-mechanical system? I use all types of
systems, but I find that the electric savings using a fully
electronic system is so small, that it is not worth the effort and
expense of the equipment.
Should I make the body out of fiberglass, carbon
fiber, aluminum or what else? These are basic car design
issues. I think that fiberglass is too heavy. Perhaps a lightweight
frame and then use shaped Styrofoam covered with a very thin coating
or thin plastic. UV sunlight can destroy many types of plastic in
just a year or two. I believe that carbon fiber is vastly over rated
for a number of reasons. Though in theory, carbon fiber is extremely
light and at the same time, is substantially stronger than steel, I
have noticed that all too often, parts made of carbon fiber are not
well designed and thus the potential weight advantage is not
achieved. Further, if a carbon fiber component is not well
engineered, it can, in fact, fracture. In general, the material that
you feel most comfortable and most experienced to work with is
probably the best material to use, but you should always, at all
phases of both design and construction, keep weight down, but at the
same time, do not compromise safety. I have seen strong, effective
vehicles made out of a light weight tubular frame with stretched and
shrunk thin film mylar used for the side and rear panels. The problem
of mylar is that it is greatly effected by UV light and degenerates,
under normal conditions, in less than two years. I have also seen the
same using thin canvas.
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