Experiment - Initial Test 10/19/07

Experiment: Wireless Charger.

Goal: Demonstrate coil-to-coil induced voltage.

Materials: 2 80mH Inductors

Equipment: 12VAC power supply, Oscilloscope

Configuration: transmit 80mH inductor, receive 24mH (windings undetermined) in fixed positions approximately 2 inches center-to-center, approximately 0.5 inch radii.

Test #1:

Source: 12VAC, 1kHz (connected to primary coil).

Voltage induced on secondary: 50mVAC

Test #2:

Source: 12VAC, 10kHz (connected to primary coil).

Voltage induced on secondary: 100mVAC

Test #3:

Source: 12VAC, 100Hz (connected to primary coil).

Voltage induced on secondary: Negligible

Test #4:

Source: 12VAC, 10MHz (connected to primary coil.

Voltage induced on secondary: 100mVAC (same as @ 10kHz).

Conclusions:

Relationship between frequency on the primary side and the induced voltage in the secondary is due to resonance, this relationship is not linear. Coils are essentially RL circuits, need further analysis from this perspective.

Further Questions:

What is the ideal voltage, frequency, coils distance, geometry of coils relative to each other and of coils themselves (is an elongated solenoid the best shape? Maybe something flatter or secondary normal to primary.) Can secondary coil be minimized? What is ideal turns ratio? Effect of L needs to be determined. Is attenuation between coils linear?

Would need to determine a rectification scheme. Kelly Campbell suggests Op-Amp for low voltage rectification instead of diodes. This will not work because it would require more power on the secondary side than is available.

Estimated Timeline:

I – Initial prototyping.

I.1 [10/07-11/15/07] Design experiments to determine the following:

a. Ideal operating voltage for primary coil.

b. ideal operating frequency for primary coil.

c. ideal windings and turns ratio for primary & secondary.

d. ideal geometry for device; e.g. placement of coils relative to each other and ideal geometry of coils themselves).

e. impact on RL effect of coils on power transmission.

I.2 [11/16/07-12/15/07] Design, construct and test prototype device based upon preliminary findings.

I.3 [1/15/08-1/31/08] Design, construct and test rectification stage.

I.4 [2/1/08-2/15/08] Design, construct and test charging circuit for battery.

II – [2/16/08-4/08] Fine tuning of working device.

II.1 Scale-down secondary coil to fit into portable device.

II.2 Scale-down rectification & charging circuits.

II.3 Streamline primary circuit of charger and build enclosure or incorporate into existing enclosure.