What I intend to do is to make a resonant tank circuit and see if we can achieve maximum efficiency. Since the primary coil current for the coupling transformer/resonant-choke is minimal, have chosen to use a low power H-bridge, L298 (max 4 amps).

Just completed the schematic layout for this project. A microprocontroller will generate a low frequency (say, 0.5Hz @ 50% duty cycle) and then the polarity is alternately reversed by the H-bridge and provided to the coupling transformer at a high frequency (close to resonant frequency of a water cell). I plan to initially vary this frequency manually and later will think about automating it eg; scan through a frequency window and lock itself at resonance. In the circuit I have separated the logic voltage and the drive voltage for coil excitation. The excitation voltage can be from a variable power source (9 to 24VDC) whereas the logic voltage (for the microcontroller etc will be derived from it at 5VDC.

H-bridges that are cheap and affordable,

1. L298, dual and when run in parallel can handle upto 4amps
2. VNH2SP30, can handle upto 30amps.

You can get them from ebay. I am now searching for a suitable core to fabricate the coupling transformer.

RTJ Nair