Can anyone explain how my electric toothbrush charger works?

[Impret-Sir]

This may seem like a silly question, but I have wondered about this as long as I have had the brush!

The brush sits on a plastic, and therefore presumably non-conductive, post on the charger, which fits into a plastic hole in the brush's handle, After a few hours sat on this thing, somehow the brush is charged up again! There is no electrical conncection between the two. If the brush is running and you move it over the charger, the brush stops working. I have some vague idea that magnets have something to do with it, but I dont really know how!

[fo3nix]

This is basically a property known as mutual inductance:

http://en.wikipedia.org/wiki/Inductance

[Tim Baxter]

What is happening is that the base and the brush handle have copper 'windings' in them.  The base winding is energised by the main's alternating current.  Each time the current alternates and flows in the opposite direction the magnetic field (which is generated by the current) collapses and this 'induces' an electric current in the handle's windings.  The alternating current produced in the handle is then rectified (made to flow one way only) which can then charge the battery in the handle and this is what powers your brush.

If you ever get your hands on a simple transformer, (make sure it's not connected to the mains etc first) open it up and you will see the two sets of windings.  They are usually connected by soft iron laminations which aid the magnetic flow but in yours there is simply an air gap between the brush and the base.

[Impret-Sir]

Thanks for those answers, fo3nix, Im afraid I got lost halfway through the Wikipedia explanantion, my A-level physics was not up to it! Tim, your explanation was at least easier to understand, although the actual way that the current in the handle is 'induced' is still unclear to me.

[Tim Baxter]

OK, the magnetic field generated by the windings in the base unit is strong enought to travel the distance between it and the brush's windings.  When it collapses (when the mains current reverses) it 'cuts' the windings in the brush which generates the e.m.f. (voltage) in the brush windings which produces the current which charges the battery in the brush.  Any help?

[Impret-Sir]

errrrrrrrrrrr, yes, I think I get it!, lol