DC motor / generator. Jeffrey A. Meunier

Transcription

1 DC motor / generator Jeffrey A. Meunier jeffm@engr.uconn.edu

2 Electric motor An electric motor is used to convert electrical energy into mechanical energy.

3 Electric motor An electric motor is used to convert electrical energy into mechanical energy.

4 Electric motor An electric motor is used to convert electrical energy into mechanical energy. Apply DC power to cause the motor to spin.

5 Electric motor An electric motor is used to convert electrical energy into mechanical energy. Apply DC power to cause the motor to spin. DC = Direct Current, the electricity moves in one direction only.

6 Electric motor An electric motor is used to convert electrical energy into mechanical energy.

7 Electric motor An electric motor is used to convert electrical energy into mechanical energy. 1 (1) Applying voltage in one direction

8 Electric motor An electric motor is used to convert electrical energy into mechanical energy. 1 2 (1) Applying voltage in one direction (2) causes the motor to spin in one direction.

9 Electric motor An electric motor is used to convert electrical energy into mechanical energy. 1 (1) Reversing the direction of the voltage

10 Electric motor An electric motor is used to convert electrical energy into mechanical energy. 1 2 (1) Reversing the direction of the voltage (2) causes the motor to spin in the opposite direction

11 It's actually a voltage difference Any power supply is a supply of voltage difference, which is why it has two conductors, like +5 and Gnd.

12 It's actually a voltage difference Any power supply is a supply of voltage difference, which is why it has two conductors, like +5 and Gnd. A battery (cell) has + and terminals.

13 It's actually a voltage difference There is a difference of 1.5V between + and -.

14 It's actually a voltage difference There is a difference of 9V between + and -.

15 Electric generator If you spin the shaft of a DC motor, it will generate DC power!

16 Electric generator If you spin the shaft of a DC motor, it will generate a voltage difference! 1

17 Electric generator If you spin the shaft of a DC motor, it will generate a voltage difference! 2 1

18 Electric generator If you spin the shaft of a DC motor, it will generate a voltage difference! 2 1 Any voltage difference can be used as a source of electrical power!

19 Electric generator If you spin the shaft of a DC motor, it will generate a voltage difference! Any voltage difference can be used as a source of electrical power! Reverse the motor direction to reverse the voltage direction

20 Measuring the power output

21 Measuring the power output You'll build a wind-powered generator in your project.

22 Measuring the power output You'll build a wind-powered generator in your project. You can measure the amount of power generated by your generator.

23 Measuring the power output You'll build a wind-powered generator in your project. You can measure the amount of power generated by your generator. Power = Voltage x Current

24 Measuring the power output You'll build a wind-powered generator in your project. You can measure the amount of power generated by your generator. Power = Voltage x Current Voltage = the energy that the electrons have Current = the quantity of electrons

25 Measuring voltage

26 Measuring voltage It's easy to measure voltage with an Arduino. Just use an analog input pin.

27 Measuring voltage It's easy to measure voltage with an Arduino. Just use an analog input pin. If the the voltage is in the range 0 to 5V, the analog input value will be in the range 0 to 1023.

28 Measuring voltage It's easy to measure voltage with an Arduino. Just use an analog input pin. If the the voltage is in the range 0 to 5V, the analog input value will be in the range 0 to But we need to know the current, too. How do you find the current?

29 Ohm's Law I = V / R

30 Ohm's Law I = V / R where I is current, V is voltage, and R is resistance.

31 Ohm's Law I = V / R where I is current, V is voltage, and R is resistance. If we know V and want to find I, we need an R.

32 Add a resistor

33 Add a resistor

34 Add a resistor If you spin the motor and generate a known voltage across a known resistance,

35 Add a resistor If you spin the motor and generate a known voltage across a known resistance,

36 Add a resistor If you spin the motor and generate a known voltage across a known resistance, then you can easily calculate the current.

37 Add a resistor If you spin the motor and generate a known voltage across a known resistance, If the voltage is 1 Volt then you can easily calculate the current.

38 Add a resistor If you spin the motor and generate a known voltage across a known resistance, If the voltage is 1 Volt then you can easily calculate the current. And the resistor is 220Ω

39 Add a resistor If you spin the motor and generate a known voltage across a known resistance, If the voltage is 1 Volt Then the current is 1/220 Amps, or about 4.5 ma then you can easily calculate the current. And the resistor is 220Ω

40 We just need to measure the voltage

41 We just need to measure the voltage By that, I mean: measure the voltage difference across the resistor.

42 We just need to measure the voltage Arduino

43 We just need to measure the voltage Arduino Gnd = 0V

44 We just need to measure the voltage Arduino Gnd = 0V By connecting the bottom wire to Gnd, the top wire will have a voltage value relative to the Gnd voltage. We call the Gnd voltage 0V.

45 We just need to measure the voltage Analog input Arduino Gnd = 0V

46 We just need to measure the voltage Arduino Analog input The top wire of the motor will have a higher voltage than the lower wire as long as you spin the motor the right way. Gnd = 0V

47 We just need to measure the voltage Arduino Analog input Gnd = 0V The top wire of the motor will have a higher voltage than the lower wire as long as you spin the motor the right way. You might have to reverse the wires, depending on which way your turbine blades spin.

48 We just need to measure the voltage Just swap the Arduino wires. Analog input Gnd = 0V The top wire of the motor will have a higher voltage than the lower wire as long as you spin the motor the right way. You might have to reverse the wires, depending on which way your turbine blades spin.

49 Spin the motor Arduino

50 Spin the motor Arduino

51 Spin the motor Arduino By measuring the voltage and knowing the resistance, you can calculate the current.

52 Build the circuit like this To an analog input To a Ground pin

53 Over-voltage Supplying too much voltage could damage the input pin. This will happen if your motor generates much more than 5V. It won't.

54 A program from arduino import * usbconnect() R = 220 # or 1000 or Determine the resistance of your resistor in Ohms. It's what the color bands are. Google it.

55 A program from arduino import * usbconnect() R = 220 # or 1000 or while True: V = analogread(1) / * 5 print('volts =', V, 'Volts')

56 A program from arduino import * usbconnect() R = 220 # or 1000 or while True: V = analogread(1) / * 5 print('volts =', V, 'Volts') P = V ** 2 / R print('power =', P, 'Watts')

57 A program from arduino import * usbconnect() R = 220 # or 1000 or while True: V = analogread(1) / * 5 print('volts =', V, 'Volts') P = V ** 2 / R print('power =', P, 'Watts') This is the one you care about

58 When you abort the program with ^C If you don't use the try / except statements that I showed earlier, then be sure that you enter this into the Python Shell: >>> usbdisconnect() That will allow the usbconnect() function to complete the next time you run the program.