Methods and apparatus to power an exercise machine

1. An exercise machine comprising:

a generator to convert movement of a moveable part of the exercise machine into electric power; and

a generator power receiver to measure the power output by the generator, and to calculate a rotations per minute of the moveable part;

a mode controller to calculate a power supply duty cycle based on the power output by the generator, the rotations per minute of the moveable part, and a user selected wattage; and

a power output controller to control power provided to a console of the exercise machine based on the power supply duty cycle.

2. The exercise machine as described in claim 1 , further including the console.

3. The exercise machine as described in claim 1 , further including a power supply to receive power from a commercial power source, wherein the power output controller comprises a first rectifier and a second rectifier in a wired-OR configuration, the first rectifier coupled to the power supply and the console, the second rectifier coupled to the generator and the console.

4. The exercise machine as described in claim 3 , wherein the first rectifier is a diode.

5. The exercise machine as described in claim 3 , wherein the first rectifier is a controlled switch.

6. The exercise machine as described in claim 3 , wherein the power supply duty cycle is a pulse width modulated signal, and further comprising a converter intermediate the second diode and the generator, the converter to receive the pulse width modulated signal.

7. The exercise machine as described in claim 6 , wherein the converter is an isolated flyback converter.

8. The exercise machine as described in claim 6 , wherein the converter is a switch.

9. The exercise machine as described in claim 1 , wherein the generator includes an electromagnetic brake controlled by a resistive load.

10. The exercise machine as described in claim 1 , wherein the generator is loaded by a controlled resistive load.

11. The exercise machine as described in claim 1 , wherein the mode controller is to calculate a differential power supply current based on a power supply reference current and a measured current of a power supply of the exercise machine, and wherein the power supply duty cycle is further based on a previous power supply duty cycle, a time constant, the differential power supply current, and a previous differential power supply current.

12. The exercise machine as described in claim 11 , wherein the time constant is a first time constant, and the mode controller is further to:

calculate a torque value based on a measured brake current and the power supply reference current;

calculate a differential torque value based on a reference torque value and the calculated torque value;

calculate a brake current duty cycle based on a previous brake current duty cycle, a second time constant, the torque value, and the differential torque value, the brake current duty cycle to control resistance of a brake of the exercise machine;

output the brake current duty cycle to a brake controller of the exercise machine.

13. The exercise machine as described in claim 12 , wherein the brake current duty cycle is further based on a proportional gain value.

14. The exercise machine as described in claim 12 , wherein the mode controller is to output the brake current duty cycle as a pulse width modulated signal.

15. The exercise machine as described in claim 12 , wherein the mode controller is further to calculate the reference torque based on the user selected wattage and the rotations per minute of the exercise machine.

16. The exercise machine as described in claim 15 , wherein the reference torque is further calculated based on a mechanical constant.

17. The exercise machine as described in claim 11 , further including the console to receive the user selected wattage.

18. The exercise machine as described in claim 11 , wherein the mode controller is to output the power supply duty cycle as a pulse width modulated output.

19. The exercise machine as described in claim 11 , wherein the mode controller is further to set the power supply reference current to zero when the rotations per minute of the exercise machine is less than a rotations per minute threshold.

20. The exercise machine as described in claim 11 , wherein the mode controller is further to set the power supply reference current to zero when a rectified generator output voltage of the exercise machine is less than a voltage threshold.