Jump to content

  •  

CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.

Photo

Cooling fan vibration question

Equipment Orion
  • Please log in to reply
15 replies to this topic

#1 nhanimator

nhanimator

    Explorer 1

  • -----
  • topic starter
  • Posts: 75
  • Joined: 01 Aug 2021
  • Loc: New Hampshire

Posted 21 September 2021 - 07:55 AM

I just picked up an XT10plus and am looking at picking up a cooling fan for it. I haven't had a problem yet (other than getting a fair amount of moisture on the outside of the tube), but am new to this hobby and want to be proactive. In reading the instruction manual for Orion's fan, it states...

 

"The cooling fan should be turned on as soon as the telescope is brought outdoors before observing. It should run for approximately 15-30 minutes to properly cool down the telescope. During observing, the fan should be turned off. This is because even though it runs free from vibration, the air currents it generates in the optical tube will degrade image quality. Once the mirror has cooled to the outdoor ambient temperature, the fan will not be needed again until your next observing session."

 

I see a lot of discussion about what fans to use (computer, etc) and how to mount them to minimize vibration. But according to these instructions, that shouldn't even be an issue.

 

Thoughts?



#2 wrvond

wrvond

    Soyuz

  • *****
  • Posts: 3,513
  • Joined: 25 Sep 2014
  • Loc: West Virginia

Posted 21 September 2021 - 08:06 AM

I wouldn't spend money on any fan of that type - they are too limited in their performance. 

What I did is create a baffle plate and mount a high capacity Noctua fan on it with rubber mounts. I do leave it running the entire observing time because the moving air helps prevent dew settling on the primary.

 

IMG 3928
IMG 1603

  • SteveG and FoxIslandHiker like this

#3 Chucky

Chucky

    Surveyor 1

  • *****
  • Posts: 1,508
  • Joined: 16 Apr 2010

Posted 21 September 2021 - 01:38 PM

(( because the moving air helps prevent dew settling on the primary. ))

And secondary mirror as well
  • wrvond likes this

#4 nhanimator

nhanimator

    Explorer 1

  • -----
  • topic starter
  • Posts: 75
  • Joined: 01 Aug 2021
  • Loc: New Hampshire

Posted 21 September 2021 - 01:51 PM

I guess I wasn't clear in my OP. My question was in regards to Orion's suggestion that after the mirror is cooled (15-30 minutes after initial setup), you won't even need to run it. So whether or not a fan creates vibration shouldn't even be a concern.



#5 SteveG

SteveG

    Voyager 1

  • *****
  • Posts: 10,414
  • Joined: 27 Sep 2006
  • Loc: Seattle, WA

Posted 21 September 2021 - 02:01 PM

I just picked up an XT10plus and am looking at picking up a cooling fan for it. I haven't had a problem yet (other than getting a fair amount of moisture on the outside of the tube), but am new to this hobby and want to be proactive. In reading the instruction manual for Orion's fan, it states...

 

"The cooling fan should be turned on as soon as the telescope is brought outdoors before observing. It should run for approximately 15-30 minutes to properly cool down the telescope. During observing, the fan should be turned off. This is because even though it runs free from vibration, the air currents it generates in the optical tube will degrade image quality. Once the mirror has cooled to the outdoor ambient temperature, the fan will not be needed again until your next observing session."

 

I see a lot of discussion about what fans to use (computer, etc) and how to mount them to minimize vibration. But according to these instructions, that shouldn't even be an issue.

 

Thoughts?

I would not have purchased the Orion fan, as it is very crude compared to what you can get for very cheap. Here is a list of fans from a quick search. The "quiet" gets you vibration free operation. These come with rubber mounting screws:

https://www.quietpc.com/80mmfans

 

You only need about 30 cfm for up to a 12" reflector. 

 

If you keep the Orion, you can use aftermarket rubber screws found here:

https://www.frozencp..._Silencers.html

 

And finally, you should consider making a rear baffle, and mounting that to the back of your scope with the fan mounted to the baffle - lots of examples here on CN.

 

Yes, you need the fan running while viewing. It makes a very noticeable difference.


  • izar187 and wrvond like this

#6 wrvond

wrvond

    Soyuz

  • *****
  • Posts: 3,513
  • Joined: 25 Sep 2014
  • Loc: West Virginia

Posted 21 September 2021 - 02:02 PM

I guess I wasn't clear in my OP. My question was in regards to Orion's suggestion that after the mirror is cooled (15-30 minutes after initial setup), you won't even need to run it. So whether or not a fan creates vibration shouldn't even be a concern.

Again, leaving the fan on will reduce or eliminate the formation of dew on your mirrors.

 

If dew is not an issue, then by all means, turn the fan off after the mirror has had time to cool if you wish.


Edited by wrvond, 21 September 2021 - 02:04 PM.


#7 nhanimator

nhanimator

    Explorer 1

  • -----
  • topic starter
  • Posts: 75
  • Joined: 01 Aug 2021
  • Loc: New Hampshire

Posted 21 September 2021 - 02:06 PM

I would not have purchased the Orion fan, as it is very crude compared to what you can get for very cheap. Here is a list of fans from a quick search. The "quiet" gets you vibration free operation. These come with rubber mounting screws:

https://www.quietpc.com/80mmfans

 

You only need about 30 cfm for up to a 12" reflector. 

 

If you keep the Orion, you can use aftermarket rubber screws found here:

https://www.frozencp..._Silencers.html

 

And finally, you should consider making a rear baffle, and mounting that to the back of your scope with the fan mounted to the baffle - lots of examples here on CN.

 

Yes, you need the fan running while viewing. It makes a very noticeable difference.

Thank you very much for the advice. Will look into those options. As I wrote in my OP, I haven't bought the fan but was considering it.

I wonder why they suggest that you don't need it after cooling. That would seem like it would cause problems and thus lead to bad reviews.



#8 SteveG

SteveG

    Voyager 1

  • *****
  • Posts: 10,414
  • Joined: 27 Sep 2006
  • Loc: Seattle, WA

Posted 21 September 2021 - 02:12 PM

I guess I wasn't clear in my OP. My question was in regards to Orion's suggestion that after the mirror is cooled (15-30 minutes after initial setup), you won't even need to run it. So whether or not a fan creates vibration shouldn't even be a concern.

The Orion instructions are wrong. You certainly want to run it while viewing. At this point, vibration comes back into play. See post #2 for a good example, but I think the larger fan is unnecessary. 80 mm will do, unless you are > 12".


  • Jon Isaacs likes this

#9 SteveG

SteveG

    Voyager 1

  • *****
  • Posts: 10,414
  • Joined: 27 Sep 2006
  • Loc: Seattle, WA

Posted 21 September 2021 - 02:13 PM

Thank you very much for the advice. Will look into those options. As I wrote in my OP, I haven't bought the fan but was considering it.

I wonder why they suggest that you don't need it after cooling. That would seem like it would cause problems and thus lead to bad reviews.

Because their crude fan will cause vibrations.


  • havasman, wrvond and nhanimator like this

#10 havasman

havasman

    Voyager 1

  • *****
  • Posts: 13,190
  • Joined: 04 Aug 2013
  • Loc: Dallas, Texas

Posted 21 September 2021 - 02:13 PM

I guess I wasn't clear in my OP. My question was in regards to Orion's suggestion that after the mirror is cooled (15-30 minutes after initial setup), you won't even need to run it. So whether or not a fan creates vibration shouldn't even be a concern.

It's going to depend to some extent on the observing location's conditions. My conditions make Orion's strategy a very poor one. Ambient temps at sites where I observe continue to move through most nights and the mirror temp cannot change fast enough to keep up. So fans on all my Dobs run from the time the scope is set up until it's time to break down and go home. So there is a very critical need for vibration free operation. I think this situation of continually falling night temps is more common than a stable overnight temp. So I think attention to vibrations in this subsystem is essential.

 

First, minimize vibrations created. I also rely on Noctua fans for their low vibration operation and also their high head pressures at a flow rate. That design for head pressure allows selecting a lower operating speed to again minimize vibrations at the source.

 

Second, minimize vibration transmitted from the fan to the scope structure. I do not use rigid mounting strategies but rely on lossy mountings using string, Sorbothane and springs tuned to different resonances via 1/8" bungee cord.

 

Here again is the 120mm fan asymmetrically mounted on my XT10i. Vibration at any magnification is undetectable in the eyepiece.

 

fan_installation_small.jpg


Edited by havasman, 21 September 2021 - 02:19 PM.

  • Jon Isaacs, izar187, epee and 2 others like this

#11 Chucky

Chucky

    Surveyor 1

  • *****
  • Posts: 1,508
  • Joined: 16 Apr 2010

Posted 21 September 2021 - 03:20 PM

(( Because their crude fan will cause vibrations. ))

Compounded by how they mount it using metal screws directly attached to the mirror cell.


Edited by Chucky, 21 September 2021 - 03:21 PM.

  • Jon Isaacs, havasman, wrvond and 1 other like this

#12 Jon Isaacs

Jon Isaacs

    ISS

  • *****
  • Posts: 95,292
  • Joined: 16 Jun 2004
  • Loc: San Diego and Boulevard, CA

Posted 21 September 2021 - 08:43 PM

I just picked up an XT10plus and am looking at picking up a cooling fan for it. I haven't had a problem yet (other than getting a fair amount of moisture on the outside of the tube), but am new to this hobby and want to be proactive. In reading the instruction manual for Orion's fan, it states...

 

"The cooling fan should be turned on as soon as the telescope is brought outdoors before observing. It should run for approximately 15-30 minutes to properly cool down the telescope. During observing, the fan should be turned off. This is because even though it runs free from vibration, the air currents it generates in the optical tube will degrade image quality. Once the mirror has cooled to the outdoor ambient temperature, the fan will not be needed again until your next observing session."

 

I see a lot of discussion about what fans to use (computer, etc) and how to mount them to minimize vibration. But according to these instructions, that shouldn't even be an issue.

 

Thoughts?

 

Congratulations on your new scope.. It's a good one.. 

 

As far as Orion Instructions, that would not work for me. This is what works for me with my 10 inch Dob:

 

- I try to set it out about an hour before sunset and start the fan cooling the scope. Even in San Diego's mild climate, 30 minutes is not enough.  

 

- Cooling the mirror and scope is important for higher magnifications, the planets, double stars.  Ideally the mirror should be within 1 degree C of the ambient air temperature.  

 

-  I run the fan continuously. The air temperature often drops during the evening, the mirror and scope need to track the air temperature.

 

- Vibration is a big concern.  There are various ways to mount the fan so vibration is not an issue.  I use a fan made by Floyd Blue more than 15 years ago.  It's a fully baffle design, it seals the back of the scope so all the air flows across and around the mirror and up the tube.  

 

The fan is mounted to a 0.060" thick piece of ABS plastic and it is mounted to the scope using Velcro.  The Velcro provides the vibration isolation. It works, I use 820x on very close doubles, it's vibration free.

 

IMG_21092021_184554_(1024_x_700_pixel).jpg

 

The hex bolts replaced the locking screws on the mirror cell. I use them for feet to stand the OTA on the floor.

 

Jon


  • epee, Chucky and wrvond like this

#13 nhanimator

nhanimator

    Explorer 1

  • -----
  • topic starter
  • Posts: 75
  • Joined: 01 Aug 2021
  • Loc: New Hampshire

Posted 22 September 2021 - 06:01 AM

Because their crude fan will cause vibrations.

That makes sense. Usually when a company sells a lot of products under their name, not all are of equal quality.



#14 epee

epee

    Aurora

  • *****
  • Posts: 4,727
  • Joined: 30 Nov 2006
  • Loc: Suh-van-nuh, Jaw-juh

Posted 22 September 2021 - 07:48 AM

Congratulations on your new scope.. It's a good one.. 

 

As far as Orion Instructions, that would not work for me. This is what works for me with my 10 inch Dob:

 

- I try to set it out about an hour before sunset and start the fan cooling the scope. Even in San Diego's mild climate, 30 minutes is not enough.  

 

- Cooling the mirror and scope is important for higher magnifications, the planets, double stars.  Ideally the mirror should be within 1 degree C of the ambient air temperature.  

 

-  I run the fan continuously. The air temperature often drops during the evening, the mirror and scope need to track the air temperature.

 

- Vibration is a big concern.  There are various ways to mount the fan so vibration is not an issue.  I use a fan made by Floyd Blue more than 15 years ago.  It's a fully baffle design, it seals the back of the scope so all the air flows across and around the mirror and up the tube.  

 

The fan is mounted to a 0.060" thick piece of ABS plastic and it is mounted to the scope using Velcro.  The Velcro provides the vibration isolation. It works, I use 820x on very close doubles, it's vibration free.

 

attachicon.gifIMG_21092021_184554_(1024_x_700_pixel).jpg

 

The hex bolts replaced the locking screws on the mirror cell. I use them for feet to stand the OTA on the floor.

 

Jon

Jon,

The Velcro attachments that you use are not apparent in your photo; do they stick to the raised areas of the cell; where the locking and collimating bolts are located?


  • Jon Isaacs likes this

#15 Jon Isaacs

Jon Isaacs

    ISS

  • *****
  • Posts: 95,292
  • Joined: 16 Jun 2004
  • Loc: San Diego and Boulevard, CA

Posted 22 September 2021 - 08:11 AM

Jon,

The Velcro attachments that you use are not apparent in your photo; do they stick to the raised areas of the cell; where the locking and collimating bolts are

 

Right. 

 

There is an outer ring and they fit between the bolts.

 

Jon


  • epee likes this

#16 DHurst

DHurst

    Mariner 2

  • *****
  • Posts: 275
  • Joined: 10 Mar 2006

Posted 22 September 2021 - 06:36 PM

I use the same fan as Jon.  Works quite well!




CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.


Recent Topics





Also tagged with one or more of these keywords: Equipment, Orion



Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics