Inductive coupling help reqd..

There are one or two electric toothbrushes that use this trick to charge the battery in the brush from 240V 50Hz.

Efficiency IS an issue. There are more ramifications that a few cents per year extra in power consumption. Melting plastics for one thing (albeit for higher power devices).

Makes for smaller coils for one thing. Depends on how "portable" you want to make the device.

Again, don't disregard little things like this. I replaced my cordless drill battery with an SLA type I had on hand, because it was quick and easy and I couldn't be bothered going out to buy the proper one the next day.

Nearly 6 pounds in the battery alone. Great capacity, but ruins the balance and more importantly, the aesthetics of the tool.

Pretty much, since 50/60Hz doesn't couple too well. Mainly because you'd need oodles of turns to get up to the required inductance and also because it's a fixed frequency.

The trick is to make the setup series resonant. Typical frequencies at this power level are in the 50-100kHz range.

O.K. Does anyone have any pointers for a reference design? My google searches have come up with very little...

Haven't seen any on the web and I can't disclose any stuff I did for clients. Just look for series resonant converters. The trick is to mitigate the inevitable huge leakage inductance that results from the coils' poor coupling but you can only do that for one side. That would usually be the input side.

Oops, try this,

I will leave unsaid but hinted at my utterly derogatory assertions about worrying over the aesthetics of a tool over the function.

Aesthetics are important too. Alas most "designers" care only about aesthetics.

I sold my last property to a chippie (builder). He only uses 12V tools. Initially I scoffed, until I spent an entire day working with my 18V drill held above my head.

Cheers Terry