Secondary coil of toothbrush has two levels of coils, the second having a larger diameter than the first. One possibility for this coil design is to have the coil widen as the magnetic field widens - since this device operates in a fixed position when charging. The voltage measured across the the coil when in the charging position was in the hundreds of millivolts. The voltage measured across the battery charging terminals was approximately 2.21V. This would indicate that the secondary coil is not self resonant and requires support reactances for the circuit to achieve resonance. I was unable to disassemble the base, charging unit (transmitter) because it is encased in epoxy. I determined that the base unit oscillates at 80kHz.
Charging cell phone with Sonicare toothbrush –
measurements: Vterm=2.21V, Iterm =0.165mA
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