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dew prevention on big dob


seven_legs
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hello all


 


I've got a 350mm goto skywatcher dob which I soon to be taking to the dark site. I have no dew protection at the mo. wondered if anyone go this scope and what they use.  contacted first light optics and they told me,'with large dobsonian scopes and newtonians you can't use a dew tape for the primary mirror as the scopes are simply to big'. 


 


thanks


 


tony


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You can get a dew controller that will do 2-4 dew bands, these can be fitted to your secondary mirror housing, your finderscope end lens and your eyepeice.


Lots of folk on here have big dobs and I'm sure they will tell you exactly what and where to get these add-ons!  :)


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What I have is a 12V DC speed controlled fan for the primary, if it's a Sky Watcher, they usually have the four holes pre drilled and tapped in the mirror cell.


 


I then have a four channel dew heater controller, which supplies the Telrad, Finder scope, eyepiece, and two ceramic resistors siliconed to the rear of the secondary mirror.


This works really well and keeps the scope dew free all night. 


 


If you need any help give me a shout.


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Hi Tony,


 


I have the Intelliscope version of this scope.


These are what I have for dew prevention.


4 port dew controller for which you can get all manner of heater bands for eyepieces and finders etc...


http://www.firstlightoptics.com/dew-prevention/hitecastro-four-channel-four-port-dew-controller.html


 


Secondary dew heater...


http://www.altairastro.com/product.php?productid=16275&cat=243&page=1


 


Light shroud which also helps keep out dew...


http://uk.telescope.com/Orion-Light-Shroud-for-SkyQuest-XX14-Truss-Tube-Dobsonian/p/109980.uts?keyword=orion%20light%20shroud#


 


I fitted three fans to the back of the primary cell to move the air up and around the mirror which helps with both cooling and dew prevention...


20140824_172859.jpg


 


I'm sure we are both going to get some great views through this nicely sized scope. :thumbsup:


 


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Pete's beast really does the subject justice.  :thumbsup:


 


The shroud makes a heck of a difference, and helps direct the air from the fans all the way up the tube. This also helps smooth out any tube currents.


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Altair Astro where trying to sell me heat pads instead of bands for my primary, but Martyn and Pete know their stuff. I'll catch up with you soon. Still loving the 10" by the way ;-)

Edited by tuckstar
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In all the years I've been doing this I don't think I have ever suffered with a dewed up primary mirror.


 


Now the secondary mirror that's a different story.


 


If you meant the secondary mirror then I would silicon on a resister not sure what rating but I can have a look later. Get one of the ceramic ones with the flat base so it sticks easy. Join the ends to a wire and run it through a dew controller.

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So folks, no heat, just creating some air movement with the primary mirror fan?

 

The primary mirror is usually right at the bottom of the longest and most efficient dew shield you can get. The tube.

 

So it is extremely unlikely to dew up anyway. See Micks post above.

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In the 3 and a bit years I have had my 8" dob, the primary has dewed up twice (the last time was 2 weeks ago at Kelling after 9 hours)!

See my signature for what I have but all advice above is spot on.

I'm currently sourcing a fan for the back of my primary, I have not spent all this money on kit to be stopped by some water!

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For Darren or anyone else looking for fans, I did some research and found what I think are the best ones for the job...


http://www.quietpc.com/afdp-8025b


 


Pretty much any fan will do, but although not the cheapest, this one is extremely quiet and vibration free, has sealed bearings, so is dust and damp proof. The suppliers told me it will work reliably in subzero temperatures and damp conditions. They even said they had actually tested it under water with no problems!


 


The supplied anti-vibration PC fixing hardware doesn't lend itself to fixing to a scope. I just used long M4 bolts with rubber washers.

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Great post... Just what I need too!


 


Got scuppered on Saturday night. ED80 Primary (objective sorry :) [edit])  and later the secondary on the 200p. Quite frustrating.


 


I will need to (or want to?) re-use the ep dew bands and controller on two different scopes.


 


Baz, out of interest have your Resistors ever fallen off? I can see they are taped too so hopefully wouldn't go far. OR is the Silicon pretty reliable and resistant (?) to the heat? Nice looking dew controller too! I am think about building one but have seen the hitecastro ones on ebay for about a tenner less than FLO so am quite tempted by that.


 


Did you use a project box? I would be interested in specs of the parts for any homemade controllers.


 


I was also considering having a go at building my own bands but am currently thinking I do not have the time to play!


 


Steve


Edited by Johnnyaardvark
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thanks everyone. got a lot to think about. I have to say I am rubbish with  DIY stuff. if clear skies on the 17th October, I will be going to belper dark for first time. Andy will be showing me the way there. glad you still enjoying the scope. so hopefully will get to see other dew prevention setup.


 


thanks again


 


tony


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Let's hope for some clear skies Tony. Don't forget first visit free then you have to become a darksite member and all will be available to you.

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so if I get a secondary heater,  then plugs into a HitecAstro four-channel, four-port Dew Controller. where do you put controller? if at base I would need a extension lead for heater, as the cable is only 15 inches long. and finally I have a Skywatcher  powertank 17Ah how long would the power last with say 2 heaters and running the scope? would I need to get another power tank?


sorry for being really thick lol


 


tony


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so if I get a secondary heater,  then plugs into a HitecAstro four-channel, four-port Dew Controller. where do you put controller? if at base I would need a extension lead for heater, as the cable is only 15 inches long. and finally I have a Skywatcher  powertank 17Ah how long would the power last with say 2 heaters and running the scope? would I need to get another power tank?

sorry for being really thick lol

 

tony

 

Hi, take a look at this, right at the bottom there are a few tables that explain about amp ratings, please note this is for the Kendrick range only, it will though serve as a guide.

 

http://www.kendrickastro.com/heaterfaq.html

 

Also, you say you have a 17 A/H battery, I do not think that will be sufficient to power a mount and x amount of dew heaters for any great length of time.  I know EQ mounts suffer horribly with low voltage drops, 17 A/H battery coupled with reduced capacity due to extreme cold up at the Belper dark site, coupled with mount usage and dew heaters, I do not think you will get long.

 

I run 5 dew heaters only from a 38 A/H battery and that lasts 3 + days in cold temperatures (it has never died on me yet at a star party).

 

HTH.

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Cables are only rca leads, ordinary phono cables so no problem. I've stuck my controller on to side of base with velcro. Can't help with battery life it's still something I'm looking at.

Edited by tuckstar
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thanks again for help.


so if I just used skywatcher tank for the goto and a 38 A/H battery for the heaters that be it. but how do I connect dew controller to 38 A/H battery? as it has a cigarette-lighter type plug.


lol told you crap at this stuff


 


tony

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