Anyone know how this puppy works? It’s got a stand attached to the electrical cord. The stand has a little hump of plastic that the toothbrush rests on. It’s solid plastic, there’s no terminals visible. Yet when you rest the toothbrush on the hump it starts charging!
It’s basically induction. You have the two halves of a transformer, with an airgap in the core.
In the base an alternating magnetic field is generated, and in the hand-held part a coil makes electricity out of it.
from How Stuff Works:
I must admit that I cannot quite picture how the field looks like. Can it be that the field looks like the windings of a toroidal coil, with the actual coils being two concentric horizontal flat coils in the same plane? Intuitively it seems to me that such an arrangement would create quite a leaky field.
I would have preferred a horse-shoe like base (with a proper iron core) and the final piece of the horse-shoe formed by the toothbrush. It seems to me like a more contained field. But I’m no designed of toothbrushes, and I haven’t really designed any transformers at all.