Am I doing something wrong, or isn't cast iron really compatible with induction?
Hardware : le creuset pan, smeg induction stove top.
I recently received a NuWave (as seen on TV) cooktop unit as a gift. Most of my cookware isn't induction-friendly. However, my Lodge cast iron seems to work like a charm. I use my skillets on it as well as enamel coated Dutch ovens and haven't seen any problems. I usually use the skillets to sear steaks with the NuWave and then finish in the oven, so maybe I'm not using it as long as you are to experience the hot spots. I'm really happy with the induction cook top and now use it more often than my Jennair range. (I'm biased now since I use gas at work and have come to dislike the electric coils I have at home.)
Cast iron is a poor conductor of heat. What cast iron has is tremendous thermal capacity so once it's hot it stays hot. If there is any mismatch in size between the pan and the induction burner, the cast iron will have cold spots.
While my kitchen was being remodelled, I used a NuWave Pic Titanium induction cooktop as my only "burner". It worked very well with cast iron (Lodge). It did have some problems when I used it with a 12" (Caphalon?) enamelled cast iron pan at the edges. I think the heating element is only 9 1/2 inches even though the 12" pan fit on the burner just fine.
I still occasionally use the NuWave for simmering or when I want an extra burner. I've never had a serious issue and I've never noticed a "donut" shaped heat profile.