Electric Vehicles - The EV, What Makes it Tick?

Electric cars are something that show up in the news all the time. So - what is inside these unique creatures?

The heart of an electric car is the combination of:

Electric cars can use AC or DC motors:

A simple DC controller connected to the batteries and the DC motor. If the driver floors the accelerator pedal, the controller delivers the full 96 volts from the batteries to the motor. If the driver takes his/her foot off the accelerator, the controller delivers zero volts to the motor. For any setting in between, the controller "chops" the 96 volts thousands of times per second to create an average voltage somewhere between 0 and 96 volts.

The Basic elements of a DC Electric Car - Motor, Controller, Batteries, and throttle Potentiometer

A majority of the electric cars on the road today are "home brew" conversion vehicles. A typical conversion uses a DC controller and a DC motor. An AC controller hooks to an AC motor. Using six sets of power transistors, the controller takes in 300 volts DC and produces 240 volts AC, 3-phase. The controller additionally provides a charging system for the batteries, and a DC-to-DC converter to recharge the 12-volt accessory battery.

An AC Motor Design System typically uses a 3-Phase System

If the motor is a DC motor, then it may run on anything from 96 to 192 volts. Many of the DC motors used in electric cars come from the electric forklift industry.

If it is an AC motor, then it probably is a three-phase AC motor running at 240 volts AC with a 300-volt or higher, battery pack.

DC installations tend to be simpler and less expensive. A typical motor will be in the 20,000-watt to 30,000-watt range. A typical controller will be in the 40,000-watt to 60,000-watt range (for example, a 96-volt controller will deliver a maximum of 400 or 600 amps). DC motors have the nice feature that you can overdrive them (up to a factor of 10-to-1) for short periods of time.

That is, a 20,000-watt motor will accept 100,000 watts for a short period of time and deliver 5 times its rated horsepower. This is great for short bursts of acceleration. The only limitation is heat build-up in the motor. Too much overdriving and the motor heats up to the point where it self-destructs.

AC installations allow the use of almost any industrial three-phase AC motor, and that can make finding a motor with a specific size, shape or power rating easier. AC motors and controllers often have a regen feature. During braking, the motor turns into a generator and delivers power back to the batteries.

The DC-to-DC converter is normally a separate box under the hood, but sometimes this box is built into the controller.

Any electric car that uses batteries needs a charging system to recharge the batteries. The most sophisticated charging systems monitor battery voltage, current flow and battery temperature to minimize charging time. The charger sends as much current as it can without raising battery temperature too much. Less sophisticated chargers might monitor voltage or amperage only and make certain assumptions about average battery characteristics. A charger like this might apply maximum current to the batteries up through 80 percent of their capacity, and then cut the current back to some preset level for the final 20 percent to avoid overheating the batteries.

Usually, the person doing the conversion has a "donor vehicle" that will act as the platform for the conversion. Almost always, the donor vehicle is a normal gasoline-powered car that gets converted to electric. Most donor vehicles have a manual transmission.

Charging Current

When lead-acid batteries are at a low state of charge, nearly all the charging current is absorbed by the chemical reaction. Once the state of charge reaches a certain point, at about 80 percent of capacity, more and more energy goes into heat and electrolysis of the water. The resulting bubbling of electrolyte is informally called "boiling." For the charging system to minimize the boiling, the charging current must cut back for the last 20 percent of the charging process.
 
The person doing the conversion has a lot of choices when it comes to battery technology. Lead Acid, Nickel-Metal Hydride, Lithium Ion, & Lithium Polymer. The vast majority of home conversions use lead-acid batteries, and there are several different options: Marine deep-cycle lead-acid batteries, Golf-cart batteries, and High-performance sealed batteries. The batteries can have a flooded, gelled or AGM (absorbed glass mat) electrolyte. Flooded batteries tend to have the lowest cost but also the lowest peak power.

Electric Vehicle Challenges

The mission of the EV Challenge is to energize high school students about engineering through a real world electric vehicle program.
Hosted by Waterloo Engineering, the Waterloo Electric Vehicle (EV) Challenge encourages students to design and test their own electric car in an annual endurance competition.
Founded in 2001, the Perth eV Challenge requires competitors to design, build and race a vehicle that can travel the furthest distance in 1 hour using only 432 watt-Hours of battery capacity.

Great Links


For More information, Contact your local EV Organization:

The Electric Vehicle Society of Canada is a non-profit group. We are concerned with clean, safe, and innovative electric transportation. We Hold monthly meetings at Centennial College, Toronto, on the third Thirsday, except July & August.

The Electric Vehicle Society of Canada
21 Burritt Road, Toronto, Ontario M1R 3S5

Howard Hutt, President

416-755-4324 or hwhutt@rogers.com

We offer Year Membership to Corporations & Schools for $100.00 Individuals at $30.00, Seniors for $20.00, and Students are Free.

©2006