Cooling Fan

[RichardK (Richard)]

My old DOB was very simple (and worked well) but didn't have a fan. The one I am cosidering from Bintel does have a fan.

Does a fan do very much if I put the scope outside a while before I want to use it?

Richard

East Feluga via Tully

Innisfail > 150mm overnight! Life in the tropics!!!!

[DavidU (Dave)]

Richard, a cooling fan is a must for Newtonian scopes. The mass of the mirror is quite large and the sooner it is cooled toward ambient temp the better. A mirror who's temp is close to the air temp will show better images as it is not radiating warm currents of air (like what a mirage over a hot desert or road.)
I would always use a fan on a Dob or any scope with mirrors with any mass.

[mr bruess]

a hot mirror will deform slightly so you need cooling fan to bring up to original form

[Robh (Rob)]

Originally Posted by RichardK

Does a fan do very much if I put the scope outside a while before I want to use it?

Richard,

There will be convection currents as long as the mirror is hotter than the outside air. The hotter the mirror the worse the disturbance. Leaving the scope outside for a while will help speed the cooling process. As the air temperature drops, the mirror continues to lose heat. Even when the air temperature levels off, the mirror will still take a while to stabilise. The purpose of the fan is not only to speed the cooling of the mirror but to remove the convection eddies directly above the mirror.

Regards, Rob

[steve000 (Steve)]

Def cooling fan....

My main point of this post is you dont "need" an "astro" cooling fan.

Places such as MSY, Umart, Ebay, PC case gear etc all sell good priced pc fans usually an 80mm or 120mm is what you need.

if you scope already is powered then ur set, make a simple connector for the 12v and ur good to go. if its not powered then an astro fan maybe a good choice. Or you can diy for around $20..
This power adapter.
http://cgi.ebay.com.au/Car-Wall-Char...item2eb3f3e9ed

Cut the end off this socket.
http://www.jaycar.com.au/productView...g&form=KEYWORD

Then cut the plug off this fan and join it to the cut end of the socket.
http://cgi.ebay.com.au/80mm-Cooling-...item2eb11ad014

OR put this plug on the end of the fan http://www.jaycar.com.au/productView...e&form=KEYWORD

Total cost around $15

I can make it for you if you want, OR if you in brissy i can show you how to make it if you are serious I can do a better diagram.

[Liz]

Hi Richard .... my Dob didnt have a fan, and one of the guys in the group popped 2 little computor fans on the back, and attached the power leads, so am right ....... as long as I remember to turn them on.


ps. dont think you were coming to Ravenswood camp next weekend, but 99% cancelled due to our beautiful liquid sunshine.

[RichardK (Richard)]

Thanks for the replies. I think the scope will come with a fan - the information was good.

Richard