I'm not home right now, I'm on vacation actually. It's really a matter of how much coil is being used to heat. You only need a quarter inch or so of active heating area to get the VapCap hot. If there is no ferromagnetic material being inserted that far into the coil then it will only draw enough current to power the portion of the coil that has the ferromagnetic material inside it. If you were to modify your coil you could limit the maximum load of the circuit that way. But I don't know anything about induction coil design, and instead have chosen to just use a power supply rated for the IH with the coil supplied based on the manufacturer rating. If you know how to design a coil to only be able to output 60watts maximum then all you need is a 60watt supply. But again, I've maxed out a 10a supply until it clipped out with the provided coil, which is why I upgraded to a 12. But that was rev1 of the design. I've since gone with a MOSFET and a momentary switch and a ceramic spacer to limit the amount of VapCap that gets inserted into the coil.

It's not that a smaller supply doesn't work... Clearly, everyone runs a 6A supply in this sub, but like I said it's a safety issue. I just don't want a fellow DynaFan getting hurt because they use a heater incorrectly and it doesn't have a PS that can compensate for that.

This is the supply I'm using. My IH is just crammed into a Newman's Own Salsa jar (medium chunky salsa). It was never meant to be the final enclosure, but I kind of liked it so I left it as is.

As far as coil diameter, it's coiled around a 16mm glass tube.