MadSci Network: Engineering

Re: How to charge electric cars?

Date: Tue Apr 28 11:02:53 1998
Posted By: Adrian Popa, Directors Office, Hughes Research Laboratories
Area of science: Engineering
ID: 893531158.Eg


Yes indeed the electric motors that drive electric cars can be used as 
generators and they are used in that mode on the General Motors EV1 
electric automobile! Electrical motors and electrical generators are not 
100% efficient, more energy must be put into them than the output power 
that they provide. The net result of putting generators on a vehicle is 
that the generator requires more mechanical power from the vehicle to 
rotate it than the electrical power that the  generator or alternator can 
produce to charge the batteries. However; there is one important exception 
to this and that is during braking..

When a conventional vehicle brakes to slow or stop, the mechanical friction 
on the brake drums and disks generates heat which is lost energy that 
was originally provided by the batteries to keep the car moving. By 
changing the electric drive motors into generators during braking, the 
energy used to slow down the vehicle can be used to generate electricity to 
help recharge the batteries.  This concept is called regenerative braking 
and it has been used on electrical railroad locomotives for many years. In 
case the electric car must stop more quickly than the regenerative braking 
can provide, electric cars also have conventional friction brakes. It takes 
a skilled operator of an electric vehicle to attempt to use only 
regenerative braking to put the maximum amount of electrical charge back 
into the battery during a braking maneuver. Onboard computers can aid the 
driver to conserve this energy usually lost as heat.

GM EV1 G a l i l e o   B r a k i n g   S y s t e m

The systems of the GM EV1 can be found at the following URL : 

All of the electric cars system are described in these Web pages including 
it's Galileo Braking System.  The following  information is from the Web 

"The electric car's advanced "brake-by-wire" system eliminates almost 100 
parts (compared to a standard hydraulic system). This system interprets 
electronic signals when the brake pedal is pressed, calling for the 
hydraulic modulator to apply pressure at the front calipers to stop the 
car. The rear braking system is electronically activated and has an 
automated parking brake. Intelligent software constantly monitors driving 
conditions, engaging traction control or anti-lock brakes to help avoid 
hazardous situations. 

In addition to providing power assist, traction control, anti-lock, tire 
inflation and system diagnostics monitoring, the Galileo Braking System 
also includes a new concept in braking: regenerative braking. It works like 
this: when you step on the accelerator of the electric car, you get an 
energy discharge from the battery. When you brake, you are actually 
capturing kinetic energy from the vehicle (with the motor) and putting 
energy back where it originally came from--into the battery. Depending on 
how you drive, you may actually improve your range."

While regenerative braking can extend driving range, several new types of  
batteries are under development  along with hybrid vehicles that combine 
internal combustion engines and electric motor/generators that can 
significantly increase the range of current electric vehicles.

Best regards, your Mad Scientist
Adrian Popa

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