Friday night - finally a good test of my dew heating for the 12" reflector on dob mount.
I have a Thousand Oaks controller (four controlled channels, one fixed 12V channel), Dew Not heater straps and the AstroSystems DG-1 (fixed secondary mirror heater).
Conditions were quite dewy with low fog rolling in and out. Temp dropped to around 3 deg C.
The secondary heater (on the fixed 12V channel) and the heated eyepiece box (a 10" Dew Not heater laid in the bottom of the box powered from one of the controlled channels) worked well. See other threads on these two items.
On the three remaining controller channels, I had a heater strap on the finderscope objective lens, a heater strap on a 2" eyepiece (30mm wide angle) and one on a 1.25" eyepiece (10mm Vixen LV).
I set the controller to around 50% on all channels and did not see a hint of dew formation all night. I suspect I could back them off to about 25% and still get a good result.
I usually cap the eyepiece top when not in use, but at one stage I went for coffee for half an hour during a period of fog and found the cap in my pocket. When I came back out and observed the 2" in the focusser, the eyepiece was clear of any condensation.
I powered all from a gel battery - an 18AHr from Jaycar. The lot drew under 2amp and was still going strong after about eight hours.
I'm a happy little vegemite!
