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  • No-contact chargers for electric toothbrushes

    Jennifer Murphy

    Jennifer Murphy

    @jennifer-murphy-CyNi39
    Updated: Oct 26, 2024
    Views: 1.2K
    Most rechargeable devices have some sort of electrical (physical) connection with a power source. My electric toothbrush is in a sealed plastic case with no physical contacts. It gets recharged in a plastic base. I assume that the base unit senses the presence of the toothbrush handle and starts emitting an oscillating magnetic field, which induces an electrical current inside the handle, which charges the battery.

    Is that correct?

    I imagine that they choose a sealed base unit because the toothbrush is subjected to a lot more water and other fluids than, say, an electric razor. The sealed handle and base prevent moisture from getting to the electronics.

    I am wondering why this method of recharging devices is not more common. Is magnetic induction a less efficient way of transferring power than a physical connection? Are there other drawbacks?
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  • lal

    MemberMar 16, 2015

    You have answered the question yourselves. Wireless charging is less efficient, costlier and requires comparitively complicated circuitry.

    Oscillating magnetic fields is what transfers energy between the source and load in this case. But, the problem with magnetic fields is that, those cannot be directed as easily as electric current. Electric current would follow the copper (or any conductor) path across which a potential difference is applied (I meant copper wire). A magnetic field on the other hand spreads around the source which creates it. Yes, it can be controlled to some extent by using materials which have less resistance toward magnetic flux. But then that doesn't becomes equivalent to wireless charging. In wireless, the medium is supposed to be air.

    Further, the primary induction coil has to create very high frequency electromagnetic waves which requires a driver. At the secondary side again the induced high frequency output has to be converted to a stable supply to charge the battery. This means more complexity and cost!

    A direct copper link between the source and load would prove to be the most efficient and cheap way in most cases.
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