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To fan or not to fan, that is the question...


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Out of  all the tweaks and upgrades for a Newtonian telescope, cross flow cooling is one tweak that I would consider, having seen the results from some of my own tests.
I have a flexi-hose system which sucks the air out of the OTA, allowing  ambient air to enter the base of the scope. This increases airflow around my mirror, and after only a few minutes of use, I can clearly detect some stabilization in the thermal currents, viewed using a de-focused eyepiece. A a side-by-side comparison with another 8" Skyliner would allow for a better comparison, to see how much quicker it is before I can  use the shortest focal length eyepieces.
I`m not sure I want to fix fans permanently to my OTA, as I`m quite satisfied with the method I use at present, but my mind has a plan,  I think there's  a solution, quite simple too, but I also  think Dyson has a patent?

Edited by Charic
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This is very interesting. I hadn't really stopped to think much about how the fan provides benefits other than cooling the mirror.

In the end it is something we can try out for ourselves. My fan is plugged into a channel on my 4 way dew heater that lets me vary the power to each channel so I can run the fan at any speed any time - I'm making a mental note to do some testing!

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I have installed cross flow fans on my Newton about 3 years ago. I used to have only 3 rear mounted fans, but I struggled to get sharp images even

after more than 1 hour of cooldown. With the added cross blowing fans, the boundary layer is disrupted and the image is very clear and stable very quickly.

The scope can be used almost immediately for imaging.

 

I also added some foam padding behind the side fans to filter out dust particles. It also prevent any stray light falling onto the mirror.

 

Pieter

 

cooling_bottom.jpg

cooling_inside.jpg

cooling_side.jpg

Edited by pietervdv
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pietervdv....I love it, strap some winglets to the OTA, I`'m sure it will fly!
That's an impressive array of fans, damping and vibrations already mentioned above, but are the small fans noisy? On my setup, my fan remains off the scope,  with only a flexible hose attachment to the scope!

Edited by Charic
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10 hours ago, Ricochet said:

What size fans and primary mirror do you have? Are the fans just mounted straight to the tube or is there some sort of damping to prevent the transmission of vibrations? 

My mirror is a 10", the fans are 40 x 40 mm. I do have some rubber washers to dampen vibrations. But the fans cause nearly no vibrations at all without them,  I tried several brands before settling with these.

The fans run very quiet aswell. The only sound you hear closeby is the moving air. It was a bit tricky to install them, but it is worth the effort! 

Pieter 

 

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26 minutes ago, DRT said:

Pieter, can you please let us know the brand and model of the fans you chose to use and where to buy them?

Of course; I used these:

https://www.amazon.com/Brushless-Cooling-40x40x10mm-Sleeve-bearing-Skywalking/dp/B00BIZ7WZC

 

These are also good ones, from NoiseBlocker:

http://www.conrad.be/ce/nl/product/872056?WT.mc_id=gshop&insert=8J&gclid=CK3n_8PRhs4CFUa6GwodvuIEbg&tid=194229418_17048677258_pla-130747084378_pla-872056&WT.srch=1

 

Pieter

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In the "Sky & Telescope" thermal management article by Alan Adler, that I entered earlier in the thread, the author recommends medium-speed Sanyo fans ( two on his 8-inch Newt ), and with a row of small vent holes on the opposite side of the main tube.

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I note they are sleeve bearing. It may seem counter-intuitive but I would guess sleeve bearings will be quieter than ball bearing.

Noisy sleeve bearing fans can almost always benefit from peeling back the sticker adding a tiny drop of thin oil (e.g. sewing machine oil) and re-attaching the sticker.

I wonder how large a scope needs to be before this brings material benefits?

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On 20/07/2016 at 21:26, scarp15 said:

Here are a couple of pictures, the lead is approximately just under 2M in length and yes the jack plug is  3.5mm (mine has some PVA tape on it as it must have been pulled at some point).

 

20160720_205217.jpg

20160720_205243.jpg

Just an observation from these pictures... The power supply label shows that it originally had a typical DC power plug (centre pin +ve, outer -ve). Looks to me that it's been customised by the previous owner and the PSU is not the original. A 3.5mm mini-jack is not a standard power connector, although it does get used.

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8 hours ago, Merlin said:

In the "Sky & Telescope" thermal management article by Alan Adler, that I entered earlier in the thread, the author recommends medium-speed Sanyo fans ( two on his 8-inch Newt ), and with a row of small vent holes on the opposite side of the main tube.

Does that article have any discussion as to the benefit of blowing from one side to the other rather than radially spaced fans presumably giving a more symmetrical disruption around the edge of the mirror and dead spot in shadow of the secondary? 

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A fan angled to blow at, rather than across, the mirror should be more effective as it should cause more turbulence the requirement is to avoid laminar flow.

Given that it would have a minimal impact on light collection, supergluing cotton thread across the primary to form turbulators would be even more effective.

Neil

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20 minutes ago, Stub Mandrel said:

supergluing cotton thread across the primary

:eek:

Do you mean supergluing threads to the face of the primary or suspended across its surface by supergluing the threads to the sides of the primary and letting the tension hold the thread above the concave surface?

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6 hours ago, Stub Mandrel said:

P.S. for anyone planning to turbulate their £2,000 hand-finished mirror , that was intended as a joke... (although it probably would work)

You got me - hook, line and sinker! :icon_jokercolor:

 

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  • 4 weeks later...

I came across this 2013 youtube video showing the latest PlaneWave telescopes.

It appears they are also implementing the side blowing fans in their larger instruments.

https://www.youtube.com/watch?v=NHi6qgdXE2s

To save you some time, they mention it at the 14:10 mark

 

Pieter

Edited by pietervdv
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