odd induction cooking question
I'm a new owner of a slightly used Kenmore Elite 9991 Induction range. I've had it for about a month and am generally very happy with it, save a few minor quibbles, namely the burner layout, and the touchpad controls (I'd prefer a knob frankly).
I purchased the unit from the Sears outlet at a significant discount from the new price, and while it was sold as "new", I'm pretty sure it was a return or a tester, and that they were able to sell it as "new" under some loophole because they're also the manufacturer.
The induction cooktop has 4 burners or hobs or "work elements" as the repairman that just left called them. The specs on each from the Sears site are as follows:
Large:1-10in. 2,500/3,400 watts PowerBoost
Large:1-8in. 2,400/3,400 watts PowerBoost
Standard: 1-6in. 1,500/1,900 watts PowerBoost
Standard:1-7in. 1,900/2,600 watts PowerBoost
Each element has 2 rings to specify minimum and maximum pan size. On the 8" & 10" elements the minimum ring is 6" in diameter, whereas the max ring is (obviously) 8" and 10" in respectively.
I did the following test. I took a 6" pan (min size for both elements) and heated 1 cup of water to boil from a cold start on max power on each element. Strangely, the 8" element heats the water nearly twice as fast as the 10" element. Thinking the unit was broken, I called the sears tech out and showed him my test and he said that nothing was wrong, the 10" element has a bigger "work element" under neath it and that I needed to use a bigger pan.
Up to this point I thought the biggest circle was the most powerful element, now I'm not so sure. The same energy is being delivered to a larger coil on the 10" element than the 8" one, therefore the 10" is actually less powerful per sq inch of cook surface? Does this seem right to you guys or is my range broken?
This seems normal to me. I think that the smaller induction coil matches the size of the 6" pan better, resulting in more efficient electromagnetic coupling between the element and the pan. As I recall from physics class (many years ago), the strength of a magnetic field falls in proportion to the cube of the distance.
Did you notice where the bubbles started to form? Heat comes from one or two coils, which must be under the pan. My guess is that with the 10" burner, one of those coils is outside the 6" and thus does nothing. In fact might not even be one (assuming the control circuit detects whether a pan is present or not).
I'd suggest putting water in your largest pan (esp. a low conductivity cast iron fry pan), and watch the bubble pattern on each of the burners, and at different power settings. This should give you an idea of where the coils are.
This sounds right to me as well--ALL the poweer is used when your pan is sized to the surface/element.
If this bothers you (or you ever want to upgrade to copper cookware), you can buy the magnetic discs that convert the induction current back to conduction. Probably less efficient, but at least you do away with that spooky cold induction.