27-01-2012, 12:52 PM
Electric Cars Work
[attachment=16699]
Electric cars are something that show up in the news all the time. There are several reasons for the
continuing interest in these vehicles:
Electric cars create less pollution than gasoline-powered cars, so they are an environmentally
friendly alternative to gasoline-powered vehicles (especially in cities).
Any news story about hybrid cars usually talks about electric cars as well.
Vehicles powered by fuel cells are electric cars, and fuel cells are getting a lot of attention right
now in the news.
A Sample Car
An electric car is a car powered by an electric motor rather than a gasoline engine.
From the outside, you would probably have no idea that a car is electric. In most cases, electric cars
are created by converting a gasoline-powered car, and in that case it is impossible to tell. When you
drive an electric car, often the only thing that clues you in to its true nature is the fact that it is nearly
silent.
The Batteries
Right now, the weak link in any electric car is the batteries. There are at least six significant problems
with current lead-acid battery technology:
They are heavy (a typical lead-acid battery pack weighs 1,000 pounds or more).
They are bulky (the car we are examining here has 50 lead-acid batteries, each measuring
roughly 6" x 8" by 6").
They have a limited capacity (a typical lead-acid battery pack might hold 12 to 15 kilowatt-hours
of electricity, giving a car a range of only 50 miles or so).
They are slow to charge (typical recharge times for a lead-acid pack range between four to 10
hours for full charge, depending on the battery technology and the charger).
The Charging System
Any electric car that uses batteries needs a charging system to recharge the batteries. The charging
system has two goals:
To pump electricity into the batteries as quickly as the batteries will allow
To monitor the batteries and avoid damaging them during the charging process
Equalization
Jon Mauney points out the following:
An important feature of the charging process is "equalization." An EV has a string of batteries
(somewhere between 10 and 25 modules, each containing three to six cells). The batteries are
closely matched, but they are not identical. Therefore they have slight differences in capacity and
internal resistance. All batteries in a string necessarily put out the same current (laws of electricity),
but the weaker batteries have to "work harder" to produce the current, so they're at a slightly lower
state of charge at the end of the drive. Therefore, the weaker batteries need more recharge to get
back to full charge.
[attachment=16699]
Electric cars are something that show up in the news all the time. There are several reasons for the
continuing interest in these vehicles:
Electric cars create less pollution than gasoline-powered cars, so they are an environmentally
friendly alternative to gasoline-powered vehicles (especially in cities).
Any news story about hybrid cars usually talks about electric cars as well.
Vehicles powered by fuel cells are electric cars, and fuel cells are getting a lot of attention right
now in the news.
A Sample Car
An electric car is a car powered by an electric motor rather than a gasoline engine.
From the outside, you would probably have no idea that a car is electric. In most cases, electric cars
are created by converting a gasoline-powered car, and in that case it is impossible to tell. When you
drive an electric car, often the only thing that clues you in to its true nature is the fact that it is nearly
silent.
The Batteries
Right now, the weak link in any electric car is the batteries. There are at least six significant problems
with current lead-acid battery technology:
They are heavy (a typical lead-acid battery pack weighs 1,000 pounds or more).
They are bulky (the car we are examining here has 50 lead-acid batteries, each measuring
roughly 6" x 8" by 6").
They have a limited capacity (a typical lead-acid battery pack might hold 12 to 15 kilowatt-hours
of electricity, giving a car a range of only 50 miles or so).
They are slow to charge (typical recharge times for a lead-acid pack range between four to 10
hours for full charge, depending on the battery technology and the charger).
The Charging System
Any electric car that uses batteries needs a charging system to recharge the batteries. The charging
system has two goals:
To pump electricity into the batteries as quickly as the batteries will allow
To monitor the batteries and avoid damaging them during the charging process
Equalization
Jon Mauney points out the following:
An important feature of the charging process is "equalization." An EV has a string of batteries
(somewhere between 10 and 25 modules, each containing three to six cells). The batteries are
closely matched, but they are not identical. Therefore they have slight differences in capacity and
internal resistance. All batteries in a string necessarily put out the same current (laws of electricity),
but the weaker batteries have to "work harder" to produce the current, so they're at a slightly lower
state of charge at the end of the drive. Therefore, the weaker batteries need more recharge to get
back to full charge.