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# Solar-Powered Inductively-Coupled Circuit

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#### rWAVE

##### New Member
I am working on a solar-powered project and need to inductively couple a small voltage/current across an air gap/core to provide power for another circuit that is not physically-connected to the solar-powered source circuit.

What I am trying to do is generate 5Vdc at 100ma via a solar cell, convert it to 5Vac or whatever is necessary, inductively-couple it across an air gap to a load coil and then convert it back into 5Vdc at 50ma. There must be an air-gap between the source coil and load coil of about 0.5". The source coil and load coil must be separate from each other and are in no way connected to each other.

What I am looking for is similar to an electric toothbrush, where ac power from the toothbrush base is inductively-coupled to the toothbrush handle, converted to dc and charges the NiCD batteries within the handle. The difference with my circuit is that it must work at a very low dc level and very low current.

Early posts talked about rewinding a transformer with an iron core and the formulas necessary for wire size and number of turns. I have no idea how to tackle this design and what formulas would be appropriate. I expect the circuit to not be very efficient which is OK, since my solar-circuit can be re-designed to supply more voltage and current, if necessary. What I NEED at the load end is 5Vdc at 50ma.

I would appreciate help from anyone who can point me in the right direction.

Regards.

Your biggest problem will be the 0.5' air gap. This is VERY large for inductive coupling of low voltages, certainly a lot bigger than the gap in toothbrush chargers. Also, with these, the coils end up concentric within one another. I hope your requirements allow for that as end to end coupling is even more inefficient. You might have to generate high frequency AC and use a ferrite core to get useful power transfer.
What are you building?
Klaus

The 0.5" air gap is worst-case; with precision workmanship, 0.25" is achievable. Although the design allows for concentric coils, my goal is to try to use stacked coils (same diameter).

The project is a very low-powered toy which uses the solar station as a recharger, similar to an electric car's "magna-charge".

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