Can I have some members cooling fan solutions please ?

[spaceboy]

Hi All

I have had a look on the net but there doesn't really seem to be a wealth of suggestions so can I be cheeky and ask for some pictures of members cooling fan solutions. I am having a re-think of my current set up and need some inspiration and ideas. Asking for pictures as they often speak a thousand words. Links to other solutions that have been a help to members are also welcomed.

Thanks in advance.

[dweller25]

What type of scope ?

[hemihaggis]

Sit it outside lol

[spaceboy]

Newtonian David.

[dweller25]

Here is my cooling solution .....

[rfdesigner]

Not my scope.. (mine is yet to get it's cooling fans) but these are exceptionally good scopes so you could copy them

Corrected Astrograph - Lightweight Telescope - Lightweight Optical Support Structure Elliptical Secondary, Elliptical Flat, Elliptical Secondary, Elliptical Mirror

clear skys

Derek

[spaceboy]

Thanks guys.

David what is the material. I take it this is the older version dob and this was the original primary cover ???

[umadog]

Here's a more open design: http://www.astromart.com/images/articles/0-999/723-8.jpg

[Starlight 1]

well I use a 3400kv 3 bladed fan motor with a 4 cell li-po battery -45a brushless esc and a transmitter ,ear plugs and stand well back .

[spaceboy]

Here's a more open design: http://www.astromart.com/images/articles/0-999/723-8.jpg

I have a fan secured to the cell at the moment but I read it is better to have a baffle to send the air up the OTA. The 250PX is not so bad for cooling of the primary being perspex but tube thermals can give a false sense of bad seeing. I am trying to get a feel for what materials and mounting methods would work best. Bearing in mind possible vibration issues and how difficult it will be actually making the baffle.

[dweller25]

Thanks guys.

David what is the material. I take it this is the older version dob and this was the original primary cover ???

This is a new 8" F/6 Dob - I don't think they have ever been supplied with a rear cover - although I think the 8" F/5 is supplied with a rear cover.

The material is aluminium which I cut to size and drilled various holes for the fan and collimation screws access.

The fan cools the rear of the mirror down but the rear plate does not allow air leakage so all the air is pushed up the tube removing tube currents and the boundary layer on the mirror surface.

I run the fan even when observing at high power for planetary and it makes a big difference to the steadiness of the image.

HTH

[dweller25]

I have a fan secured to the cell at the moment but I read it is better to have a baffle to send the air up the OTA. The 250PX is not so bad for cooling of the primary being perspex but tube thermals can give a false sense of bad seeing. I am trying to get a feel for what materials and mounting methods would work best. Bearing in mind possible vibration issues and how difficult it will be actually making the baffle.

I used to have a 250PX with the same arrangement as in my picture - I found the baffle/fan system worked better by sucking air out of the bottom of the tube.

[steelfixer]

Interesting thread this.

One point though if the fan is sucking the air out of the tube will this not introduce a lot of dust into the top of the tube?

Would not it be better to have the fan blowing into the base through a filter?

Just a point as I am thinking of doing mine.

[Skills]

Very easy DIY solution from me. I sawed and sanded a spare piece of wood (from an old drawer) to use as a baffle. Attached a computer fan I bought off the internet and vecroed it to the back of the scope (it blows). Wired it up to a fan speed controller and battery pack - really easy just followed how-to-wire-up-a-computer-fan

I have no diy skills whatsoever but it does the job.

Hope that helps

Adrian

(looking at it now a lick of white paint might improve it...)

[spaceboy]

How is it fixed please Adrian

[Skills]

Good old sticky-backed vecro, used in all of my mods.

The fan came with plastic pins to attach to the board, just needed some drilled holes.

[spaceboy]

Thanks Adrian

[spaceboy]

Here is my cooling solution .....

Have you noticed any vibration ? Is there any membrane between the cell and aluminum ?

[rfdesigner]

Interesting thread this.

One point though if the fan is sucking the air out of the tube will this not introduce a lot of dust into the top of the tube?

Would not it be better to have the fan blowing into the base through a filter?

Just a point as I am thinking of doing mine.

Correct.

Fans should blow into kit ideally through filters... electronics, telescopes.. whatever.

Derek

[umadog]

I think the generally accepted technique is to blow rather than suck the air. You get better cooling this way.

About sealing the tube. The tube currents are caused by the mirror being above ambient. In particular, the warm "boundary layer" that sits on top of the primary mirror causes the bulk of your problems. Once the mirror has cooled the boundary layer goes away and you should get much better views. For this reason, you don't necessarily need to seal the rear of the scope (see below, however).

There is a lot of interesting information in these two threads:

Telescope Reviews: Reflectors and Thermal Mismanagement

Telescope Reviews: Real life experiment with fan configurations...

The boundary layer is a problem because you get slowly moving cells of warm air playing across the primary. You can see this if you defocus on a bright star when your mirror is warm or if you look through a barlow whilst pointed at the bright star. An innovative approach is to break up the boundary layer using a fan and a so-called "deflector ring". This design does require the rear of the scope to be sealed but it also requires the deflector ring. It seem that sealing the rear on its own won't work for this purpose. Autocostruttori: Yet another method for "cooling" mirrors

When everything is tamed (including the atmosphere) then this sort of thing is possible: http://www.acquerra.com.au/astro/gallery/jupiter/20100830-174829/J20100830-1748UTC-blue-lowres.avi

[jimmyjamjoejoe]

That Autocostruttori link is pretty cool. Rather than try to eliminate the heat, just controlling it and removing it elegantly. I'm still a bit wary about how much dust/pollen this might attract to the primary though, and due to the nature of the system, you can't filter it.

[Damo636]

Would a 120mm case fan be to powerful? I have a rather stylish Sharkoon one in white for the job if it works.

[rfdesigner]

Too powerful isn't a problem, in fact it's desirable. What you don't want is too weak otherwise you have to run it at full speed and that causes vibrations and noise. A BIG fan run at low speed will be near silent and have very little vibration.

Derek

[Damo636]

Excellent, thanks Derek, that's tonight's project sorted.

[spaceboy]

Went with aluminum in the end. I had some spare 1.6mm sheet so set about cutting it to shape. The one side is pre-primered so figured this would be best suited to the primary side just in case of any stray light issues. My my cousin helped me out by covering the bare aluminum side in vinyl just to tidy it up and I fitted a some what excessive 120mm fan with Gelid speed controller. As I didn't want wire straddling every where I trimmed and soldered all connections and fitted a panel socket so it can be easily hooked up to my power tank.