How do chargers work that use magnetic fields instead of contacts?

Question

Can chargers that use magnetic fields, such as tooth brush chargers, be constructed in a much larger scale? What are the pit falls to charging without contacts, excessive heat build up, loss of energy, etc. and could they be considered unsafe in any fashion, cancer causing like radar waves, produce static electricity, or could it pose a shock hazard?

Answer 1

You need to learn about transformers.

All battery chargers use magnetic fields, because they use transformers to step down line voltage to the voltage required by the batteries to be charged.  The little toy electric toothbrush uses a transformer in which the primary winding is in the base and the secondary is in the handle of the toothbrush.

This would never be needed in a larger scale application, so there is no point in scaling it up.  Most charging devices use a transformer in which the primary and secondary windings are enclosed in a metal case and the output of the secondary is fed to  a rectifier to produce the DC current needed for charging the battery.

In the toothbrush, the secondary is in the handle so it can be removed without breaking a contact.  This is useful only for toy and novelty applications such as a toothbrush, because of its vulnerability to stray magnetic fields.

Also, the electric toothbrush still has "contacts," because there is a switch in the base that turns off the primary winding when you lift the toothbrush out of the charger.

So don't worry about scaling it up.  There is no reason to, and there are extensive practical reasons for not doing so.

Answer 2

They are like 2 halves of a transformer.  The base is the primary and the toothbrush is the secondary.  There are actual windings of copper wire close to where the base and toothbrush meet.

MIT (Massachucetts Inst. of Tech.) is actually working on scaling up that technology for both more power, and more distance.

There are possible drawbacks, such as heating in metal plates when the metal is in the mag. field of the power transfer.  There would be no static produced.  The frequencies are low enough so it wouldn't be cancer causing.

.

Answer 3

Google "electromagnetic induction" for more discussions of the physics than you can read.