Hi Markus,
Is your secondary mirror glued to a post or is it in a holder?
My secondary mirror is in a holder, and I have used
THIS dew heater for 16 years without any problems. It works efficiently and reliably. Uses very little power.
I mounted the heater to the back of the mirror, and made a hole in the holder to pass the power cables through.
If you would like to see my results, I'm happy to put up some images.
