Dew heater question for explorer 200PDS

[Jannis]

I'm currently making dew heaters as my score seems like a black hole sucking in all the dew from 10km away... -.-

So, i've already made a green laser heater wich is working fine (heats laser up to ~35c over ambient temp).

And i just finnished my main OTA heater, wich can be put at any settings from 8-35W. I'm guessing this shuold be enough power to keep dew away even down to -20c?

And while i'm currently working on my guide-cam's lens-heater, it hit me... Would i need only the front of the main OTA to be heated, or would it be best with one back at the primary mirror as well?

I've been struggeling with both dew and ice on both 1st and 2nd mirror in my OTA.

out of the 4 times i was able to go out this season so far, 3 of them have been ruined due to dew (and last 1 by the full moon + some trees + 2 compyter crashes, haha), so it was really about time i sat down and started winding up that thin wire into something that coudl make heat, lol...

[milosz]

Hi Jannis,

Did you actually get the dew on the primary mirror? The tube acts as a long dew shield and you shouldn't get any dew there. Secondary might be the problem, but I'm not sure that heating the front of the OTA will help here. There are secondary mirror heaters (for example from Kendrick) but you have to be careful with them as too much heat may deteriorate your images. The best solution for dew on secondary (at leas in my opinion) is extending the tube with something lightweight (black camping mat). This will act as a dew shield and the secondary shouldn't dew.

Cheers,

milosz

[Jannis]

Yes, i actually get dew on primary too. But usually only when pointing the scope at something very high in the sky. Therefor i thought about heat around primary too, but i guess ill just have to try... :-)

[milosz]

Wow, that is really unusual to hear. I guess you would be better off with fans instead of the heater on primary. Especially 35W heater. Commercial heater strap for 20 cm aperture is around 12W.

milosz

[Jannis]

i'ts adjustable - 35W is max i dare to run through the thin cable that wasn't made as a heating cable to begin with, hehe.

it's very moist here, usually 65-98% air humidity, so i guess thats why.

been thinking about fans too, but i currently son't have any fans of that size wich also runs smooth enough that i'd like to put it on the ota. will see what i can find if heater in the front of the ota alone doesn't help.