Electric Sonic Toothbrush

[Marijn]

When low on battery, it is placed in a charger/holder and the red light comes on to show it is being charged. How is it charged without any wires or even physical contact needed from the toothbrush to the charger? It seems to be charging through thin air.

[Teddio]

The toothbrush is being charged by electromagnetic induction. An alternating magnetic field induces an electric current in a coil of wire in the toothbrush.

[Marijn]

Thank you for your answer. Could you please tell me more about electromagnetic induction?

[rojash]

Think about an ordindary transformer - it consists of two coils close together - they don't have to be connected (and in the case of an isolating transformer such as that found in a shaver socket, they are not).

An alternating current in one induces a fluctuating magnetic field which induces a current in the other. A dynamo works in the same way, except that the magnetic field fluctuates because the magnet is rotating.

OK, back to the transformer. If you take one half and connect to the mains, you get a current in the other half - without the need for connecting them. So why not put the other half inside the toothbrush? That way, all you need do is bring the tooth brush close enough to the magnetic field in order for current to flow.

[fo3nix]

Just to add a little more: the electric field in the power block produces a magnetic field.

Energy is stored in this field.

A coil of wire close by to it can pick up this energy. It then causes electrons to flow in the toothbrush's battery.

It's similar to how radio works (passing information through fields). But it only works reliably in current consumer devices at close distances.

[mibn2cweus]

. . . and furthermore

[Marijn]

Thanks for all your answers, they're much appreciated :-)

[brucec30]

And to bring you all up to date on this technology. My 2003 BMW (if I am advertising it, it won't be a good ad for BMW since it is an electrical nightmare) uses this technology for charging the key remote. It is inverting the 12 VDC to a pulsing waveform that can use a transformer (transformer doesn't work with DC voltage) and thus charging the key remote which must contain a small transformer. Since I have a key that died about a year ago (yes, I did alternate them from year to year) I guess I could open it up but I am hoping that BMW will do something when I go back to the dealership to discuss all the work that wasn't done on its last visit (I love electronics, just the bad example of transmission of alternating current applies in this instance....BMW was the one that made it bad)
:(

[Marijn]

Yeah, too much technology isn't always a good thing :-(