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Cooling Fan for a 12" Dob

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#1 asaint

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Posted 15 April 2008 - 11:53 AM

Cooling Fan for a 12" Dob

#2 Brian Gibson

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Posted 15 April 2008 - 03:47 PM

Thanks for sharing the details!

I agree that a CPU cooling fan is ideal for this application. Make sure you get one with ball bearings. My 12" GSO Sky Mentor was one of the early models that did not include a fan. I attached an 80mm CPU fan with velcro and use it with a 9V battery (also attached by velcro as shown in the photo). I used a mini-stereo jack as the connector so that I can just remove the battery when I don't run the fan. It is very quiet, vibration free and definitely improves image quality in the early hours.

Brian Gibson

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  • 2329422-Dob 80mm fan.JPG


#3 tannehill

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Posted 15 April 2008 - 10:17 PM

I'm with you on the ball-bearing design for a fan. Most of the more expensive fans seemed to be ball bearing fans, rather than sleeve bearing style. Having other features of a expensive fan seems useful, too: balanced blades in particular. A great fan with a slighly imbalanced blade will shake like a....well, it'll shake alot.

I'm going to tinker with adding a neoprene fan assembly to my Obsession now that I'm back, and I'm mulling over how to sandwich a Peltier cooling unit around it. Still in paper-design phase...

I'm surprised you don't notice any vibration even with a high-end fan, since your fan chasis looks in direct contact with the cell. What is that white material, a cushion of some sort? With my fan, just resting against the cell with some bungee, even tho it was a $30 fan, there was vibration evident at high power.

S

#4 Brian Gibson

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Posted 16 April 2008 - 08:14 AM

The white material is simply velcro tape on the four corners of the fan and the back of the mirror cell. It allows me to remove the fan if desired and may provided a bit of vibration damping. I suspect the reason I don't see any vibration is because of the 9V radio battery which runs the 12V fan at less than full speed but still provides adequate cooling.

Brian

#5 tannehill

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Posted 16 April 2008 - 10:04 AM

thanks. velcro is not bad vibration dampening material itself, I've noted also. how long does that fan last on a 9v battery on a cool night?

s

#6 Brian Gibson

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Posted 16 April 2008 - 07:22 PM

I've never really timed the 9V battery life but it usually lasts a full evening. I did notice that the fan had stopped last night after running outside for several hours in very cold conditions but it wasn't a fresh battery so not a good test. I usually grab a fresh one if I expect to have a long observing session.

Brian

#7 Mike B

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Posted 18 May 2008 - 07:21 PM

Hi Scott-

I'd printed out yer article intending to read it... then got busy! But when i finally got to it, i thoroughly enjoyed it!

My first fan adventures were on a 6" F8 tuber, so were waay easy to implement. But now i'm typically using a 15" 'Starsplitter' Dob, with a huge mirror-box. It came to me (used) with a simple PC fan in a cut-out hole in the base of the box... which i've since gasketed with velcro, more as a *noise* dampener than one for vibration. And as such, its completely sealed, so 99% of the air drives into the mirrorbox.

But i've been thinkin' along the lines of what you've done- that is, creating a "ring-baffle" air-diverter around the inside of the box to help fan-off the mirror's face with the air that's otherwise wafting uselessly up-and-past. So thanks for reinforcing & encouraging that line of thot (& hopefully *action*!)

I also much enjoyed your writing style- i smiled a lot as i was encouraged. Just the thot of them Aussies watching you stretch iridescent pink bloomers onto yer Dob... omigosh! We Yanks'll stop at nothing to reduce our tube currents!

Interesting, tho- the cylonic action you observe during cooling- is that necessarily in the direction of the fan's rotation? If i were to install the "ring-baffle" diverter in segmnets, with a slight cant to further induce that action, i'd wannna get the direction right! Whatd'yathink?

Thanks again for an excellent article!
:grin: mike b


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