Chris called it a "feature" that it only energises that portion of the pot thats over the coils. I suspect that's actually a requirement - that it doesn't activate a field outside the pot/kettle/whatever.
It has to be. Because you can lay a fork or spoon on it, that will otherwise stick to a magnet, and it won't heat the fork or spoon up. It must have something in it that detects that.
Also, after I got "checked out" on operating it, I found you can put a cast iron frying pan on it to cook up a pancake for breakfast, and the handle on the pan don't get hot from the induction. Only by what heat gets transferred from the big part of the pan that's hot, to the handle.
That new magnetic stainless steel pot my wife got will hold about 1.5 gallons of water. It'll bring that pot to a full boil in about 2 minutes on the highest setting. If you use cast iron it will bring that amount of water to a boil in about a minute and a half.
When you're cooking with it, you don't want to make the mistake of touching the rim of the pot or pan, or laying a stirring spoon on it. It's as hot as the burner on a regular stove.
I also checked the ammeter on the inverter when my wife was cooking on it and the most I've seen it pull is 9.6 amps (240 volt). You can set the temperature of the cooking to what you want, and unlike our old electric range that cycled the "burner" on and off, this one draws power constantly. But instead of, say, 1.5 kW in on and off cycles, it will start out at high amp draw, then the amps will go down when the pan gets hot and if it only takes 3 or 4 amps to keep it at that temperature, that's all it draws.
How it saves on power is by the fact that when you cook with it, the temperature of the whole pan is even and your food cooks faster. So it don't waste any energy by having to wait to heat the pan up, and the transfer heat from a hot "burner" to the pan. Otherwise, when it's going, it can pull as much, or more, power as our old stove did.
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Chris