Chapter 4:Energy Systems¶

Introduction¶

Energy Systems encompasses the disciplines of power electronics, electric machines and drives, power systems, and renewable energy. These disciplines must work together to generate, deliver, and condition power. Energy Systems covers everything between power generation and the end user, including: power electronic converters (e.g. power supplies), electric motors and generators (e.g. wind, wave, and other renewable energy generators), motor drives (e.g. hybrid and electric vehicles), and transmission systems (e.g. transformers and transmission lines).

Section Overview¶

This lab introduces DC (direct current) motors and their potential as an energy source. Later in the lab, the Mbed is implemented in a simple circuit that controls the speed of a motor. Using a variable resistor as input, an attached motor will change its speed in proportion to the change in resistance.

Objectives¶

• Mbed KL-46z.
• USB to Mini USB.
• ECE111 kit
  • L293 Motor Driver IC.
  • LED light-emitting diode.
  • DC Motor.
  • Small Rectangular Protoboard with hole in the corner.

Using a Motor as a Generator¶

An electric motor is a machine that converts electrical current into mechanical motion. A good example is an electric lawn mower motor that converts the electricity provided by the battery into the mechanical motion of the turning blades. However, in many cases the process is reversed so that the motor is a generator that converts the mechanical motion into electricity. Two common examples of this are water dams and wind turbines. It can be demonstrated easily by connecting two motors together according to the schematic in Figure.

With a partner, connect two motors together. Turn one motor and observe the reaction of the other. When one motor is turned, the mechanical motion is converted to electrical current which is transferred through the wire to the other motor which converts it back into a mechanical motion. Try turning one of the motors quickly and observing how the other motor responds.

Using a Motor to Model a Turbine¶

In the energy systems field, a turbine is a large engine that transfers energy from natural sources (wind, water, steam, etc.) into a form of energy that we can use to make electricity. To demonstrate how this works, use the motor provided in the ECE 111 kit to power an LED. In this case, the natural source of energy is going to be you! Work with a partner and connect the motor to an LED and resistor as shown in Figure . The resistor is necessary because LEDs can only handle a certain amount of current before they break. The resistor R "resists" the current to keep the LED safe. Always have a current-limiting resistor when working with LEDs. The long lead in an LED is the positive.

Schematic of a Motor as a Turbine¶

Once the motor is connected, turn the motor quickly while watching the LED. The LED should light up. Now measure the voltage generated by the motor by connecting a digital multimeter in parallel to the motor. One person should measure the voltage generated by the motor while the other person turns the motor. Find the minimum voltage necessary to turn the LED by turning the motor.

Minimum voltage necessary to power the LED is...........V¶

Now try spinning the motor as fast as you can to see how much voltage you can generate.

Controlling Motor Speed with a Potentiometer¶

In the last lab a conductive paper potentiometer along with the Mbed was used to play different frequencies through a speaker. Using a similar concept in this lab, a normal 100k Ohm potentiometer and the Mbed will be used to control the direction (forward/reverse) and speed of a motor. To help control the motor we need to use a motor driver (L293) that has been specifically designed to handle DC motors.

Program the Mbed using the same process as last week, using Lab4.bin Then connect the motor controller, potentiometer, and the Mbed according to the schematic in Figure .

Try playing around with the potentiometer and changing the direction/speed of the motor. Using a digital Multimeter, measure the voltage at pin PF0 (where the potentiometer is connected to the Mbed) with the motor at a few different settings. Record the results below.

Voltage while Motor is in highest speed forward..................V¶

Voltage while Motor is in highest speed reverse...................V¶

Voltage while Motor is stopped...................V¶

Study Questions¶

• Explain why when you use a motor as a generator it appears that not all of the mechanical energy is transferred from one motor to the other. Hint: research motor efficiency
• What is the difference between a brushed DC motor and a brushless DC motor?}
• Research and list three potential careers that use concepts learned in this lab.

Challenge¶

Use KL-46z as a Multimeter(NO VOLATGEs MORE THAN 3.30 V).