Return to the Cloudy Nights Telescope Reviews home pageAstronomics discounts for Cloudy Nights members
· Get a Cloudy Nights T-Shirt · Submit a Review / Article

Click here if you are having trouble logging into the forums

Privacy Policy | Please read our Terms of Service | Signup and Troubleshooting FAQ | Problems? PM a Red or a Green Gu… uh, User

Equipment Discussions >> Reflectors

Pages: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | >> (show all)
Sarkikos
Postmaster
*****

Reged: 12/18/07

Loc: Scotophobe Maryland, USA
Re: Thermal Issues and Fans Successes new [Re: Bob S.]
      #5600300 - 01/01/13 08:42 PM

Bob,

Quote:

The front blowing fan seems to create what is likely some semblance of laminar flow as the images definetly are improved with both fans running simultaneously. I guess I would have to do smoke tests to actually see what is going on?




There is a program that you can download to help visualize air flow in a telescope system once you enter in data points. I've never used it. Looks intimidating to me, above my current knowledge and abilities about such things.

Yep, smoke might be easier.


Mike


Post Extras: Print Post   Remind Me!   Notify Moderator  
Sarkikos
Postmaster
*****

Reged: 12/18/07

Loc: Scotophobe Maryland, USA
Re: Thermal Issues and Fans Successes new [Re: Asbytec]
      #5600319 - 01/01/13 08:54 PM

Norme,

Quote:

Mike, that set up could work provided you could move a sufficient volume of air around the mirror to disperse the layer. As Bob mentioned, some smoke tests might help. One guy tested this "lip" system on youtube, but his results seemed to barely move any air. The smoke just kind of lingered above the mirror. He might could have used more CFM.

One thing to take into account is volume. The volume of fast moving air directly coming off the fan must spread itself around the entire rear surface, move in all direction with enough CFM to actually be felt in the huge volume of space above the primary. If the air flow is too weak, you will not get disruption toward the center of the primary (thus a cross blowing fan would help.)




That's why I suggested that ideally there should be a second fan at the side of the OTA to blow air across the surface of the primary. Then at least the fan below the primary would be cooling the bottom and sides of the mirror.

In my 8" Dob, though, the bottom fan by itself is apparently enough to create a vortex circulating around the surface of the primary. I still need to take the scope back out to see how adding vent holes has affected the air flow and the image.

Quote:

Another good design seems to be 3 high volume fans blowing from the rear and out the front. It moves so much air you can feel a slight breeze out the top of the tube. It evacuates the entire volume of air inside the tube and replaces is with cooler ambient air while it cools the primary. And the low pressure force might be sufficient to draw off the boundary layer, too. You can observe crisp images through gale force winds provided it is laminar in nature and a constant density.




Yep, I still have the three-fan setup I bought on sale from Orion. It was meant for their 14" Dob, but I want to try it on my 10". That ought to move some air.

Mike


Post Extras: Print Post   Remind Me!   Notify Moderator  
beatlejuice
Pooh-Bah
*****

Reged: 04/05/11

Loc: Hamilton, ON,Canada
Re: Thermal Issues and Fans Successes new [Re: Sarkikos]
      #5600340 - 01/01/13 09:09 PM

Quote:

It's really easy to drill a series of holes along the high edge of the primary mirror in Dobs. Depending on results in my 8" Dob, I'll be doing that for my 10" and 5" Dobs next.




Mike, I also like this idea,are you thinking something like 8-16 1/4" holes or larger?

Eric


Post Extras: Print Post   Remind Me!   Notify Moderator  
Sarkikos
Postmaster
*****

Reged: 12/18/07

Loc: Scotophobe Maryland, USA
Re: Thermal Issues and Fans Successes new [Re: Scanning4Comets]
      #5600344 - 01/01/13 09:11 PM

Mark,

Quote:

Post a pic of your fan / baffle setup Mike! Here is mine. it is a 12 Volt computer fan fixed to a light flat black, (on the inside it is flat black), thick cardboard baffle / seal. I get zero vibrations and have three speeds on the fan. I set it cranked at full speed for cool-down and leave it on low when I observe or until the 8 "AA" batteries expire. I need a new 12 Volt source so the fan can stay on longer, but I don't know what other alternatives there are for a small 12 Volt battery!




I'll have to set aside some time to bring out the scope and take some pics. Here is the battery supply I use. It holds eight D-cells. The batteries last a long time. I only need to replace one or so within about a year. I try to take the 10" to my dark site once or twice each month, and I have the batteries running five or six hours each night. The battery pack has a strap to hang it from the side of a Dob mount. Apparently the battery pack is sold along with a fan now. When I bought mine a few years ago, all you received was the battery pack.

Orion Cooling Fan for Large Reflectors

I use a separate 12v battery for my dew buster strips. That battery is a PowerSonic PS-1270 F2. I keep it and the dew controller in a basket that hangs on the front of my Dob mount.

Mike


Post Extras: Print Post   Remind Me!   Notify Moderator  
Sarkikos
Postmaster
*****

Reged: 12/18/07

Loc: Scotophobe Maryland, USA
Re: Thermal Issues and Fans Successes new [Re: beatlejuice]
      #5600358 - 01/01/13 09:22 PM

Eric,

Quote:

Quote:

It's really easy to drill a series of holes along the high edge of the primary mirror in Dobs. Depending on results in my 8" Dob, I'll be doing that for my 10" and 5" Dobs next.




Mike, I also like this idea,are you thinking something like 8-16 1/4" holes or larger?




As I said, I'm not a master of tools. I just used the largest drill bit I had at the time. I drilled seven 1/4" holes spaced evenly about 1" apart. They are lined up around the OTA at the level of the edge of the primary's surface, at the uppermost position to catch the rising warm air.

Mike


Post Extras: Print Post   Remind Me!   Notify Moderator  
Scanning4Comets
Markus
*****

Reged: 12/26/04

Loc: Ontario, Canada
Re: Thermal Issues and Fans Successes new [Re: Sarkikos]
      #5600569 - 01/02/13 12:00 AM

So, I just discovered that the bigger the cell, the more current it holds. Those big "D" cells would be a lot better than the 8 "AA" batteries I am using! I'm thinking that a Lithium battery that adds up to 12 volts or NiMH would be even better than Alkaline and last even longer.

Post Extras: Print Post   Remind Me!   Notify Moderator  
azure1961p
Postmaster
*****

Reged: 01/17/09

Loc: USA
Re: Thermal Issues and Fans Successes new [Re: Scanning4Comets]
      #5600583 - 01/02/13 12:26 AM

Well I was out again in terrific typical CT garbage seeing that went from 5/10 to overcast with stratus clouds milking the contrast to pointless, but I got to evaluate my fans again...

It would seem to work like this: the turning on of the sealed 5" fan behind the primary cuts the Jovian moon flaring ( the BEST test subject ) in half. And it's not just the length of the flaring but the brightness or opacity. Now turning on the side fan along with it cleans that down to half or a third of that. The side mounted fan would seem to have negligible effects at 50x to 120x but 173x or higher and the benefit becomes more pronounced.

Tempted to say the rear fan cuts it in half and the side fan another half, but the latter at least tonight was a little more subtle: but all together real. Once the moons tightened up under both fans what was finally left was the garbage seeing over head that left the disks soft edged - Minsk flairing but soft edged. So it helps to be sure but as the old saying goes, you can't shine *BLEEP*. Such is the seeing.

It's little unreal and aggravating too that I haven't seen anything better than 5/10 seeing in five weeks.

Five weeks.

Pete

Edited by azure1961p (01/02/13 12:26 AM)


Post Extras: Print Post   Remind Me!   Notify Moderator  
rlmxracer
sage
*****

Reged: 11/09/11

Loc: Motocross Mecca , CA
Re: Thermal Issues and Fans Successes new [Re: azure1961p]
      #5600596 - 01/02/13 12:44 AM

Thanks for the report Pete. I should get three nights of testing this weekend. I'll try a few differnt things and report back. It's looking like I'll end up with a hole in the side of my scope.

Edited by rlmxracer (01/02/13 12:44 AM)


Post Extras: Print Post   Remind Me!   Notify Moderator  
Tom and Beth
Post Laureate


Reged: 01/08/07

Loc: Tucson, AZ
Re: Thermal Issues and Fans Successes new [Re: Scanning4Comets]
      #5600597 - 01/02/13 12:47 AM

Quote:

So, I just discovered that the bigger the cell, the more current it holds. Those big "D" cells would be a lot better than the 8 "AA" batteries I am using! I'm thinking that a Lithium battery that adds up to 12 volts or NiMH would be even better than Alkaline and last even longer.



I didn't read the whole thread, so if these are covered already, forgive me

You could put a rechargeable 12V battery in the rocker. 7AH to 18AH, for example, doesn't take up much space. the 7AH size makes a good counterweight.

As for the fan speed control: I control the speed using a potentiometer within reach of the Ep. Since I built it, I see these units meant for computers where the entire circuit board is already built, and cost 5 bucks.


Post Extras: Print Post   Remind Me!   Notify Moderator  
azure1961p
Postmaster
*****

Reged: 01/17/09

Loc: USA
Re: Thermal Issues and Fans Successes new [Re: rlmxracer]
      #5600636 - 01/02/13 01:22 AM

Quote:

Thanks for the report Pete. I should get three nights of testing this weekend. I'll try a few differnt things and report back. It's looking like I'll end up with a hole in the side of my scope.




Just make sure a full 1" of the three inch fan is BELOW the mirrors reflected surface. Essentially so the bottom 1" of the fan is blowing the the side of the mirror. This forces the remaining two inches above the mirrors surface to powerfly blow the boundary layer off. If you have the tip of the 3" hole just above the mirrors surface it's a wasted exercise as the ai blows clean over the boundary layer doing nothing at all. You'd think it was close enough like the cyclonic wind off the fan would disrupt it anyway or at least partially. It did NOTHING. You need a third of the fan blowing on the side of the primary but believe me this works Wonderfully.

Good luck!!!!

Pete


Post Extras: Print Post   Remind Me!   Notify Moderator  
rlmxracer
sage
*****

Reged: 11/09/11

Loc: Motocross Mecca , CA
Re: Thermal Issues and Fans Successes new [Re: azure1961p]
      #5600730 - 01/02/13 04:46 AM

Thanks for the tips. Did you ever try it without the holes on the opposite side of the tube having the rear fan also blowing up the tube?

Post Extras: Print Post   Remind Me!   Notify Moderator  
Sarkikos
Postmaster
*****

Reged: 12/18/07

Loc: Scotophobe Maryland, USA
Re: Thermal Issues and Fans Successes new [Re: Scanning4Comets]
      #5600816 - 01/02/13 07:54 AM

Quote:

So, I just discovered that the bigger the cell, the more current it holds. Those big "D" cells would be a lot better than the 8 "AA" batteries I am using! I'm thinking that a Lithium battery that adds up to 12 volts or NiMH would be even better than Alkaline and last even longer.




My experience with NiMH batteries is that they do not last very long. I have various red lights and other accessories which use AAA or AA NiMH batteries. I need to recharge them nearly everytime before I go to my dark site. The old-fashioned D alkaline batteries last much, much longer, at least in the 8-pack power supply for fans.

At one time I shopped around for rechargeable D batteries. IIRC, they are rather expensive and most chargers don't accommodate D batteries. But the old-style D's are cheap and last very long, a year or longer in my experience. So what's the point of getting NiMH's? I don't go "green" when it don't make sense.


Mike


Post Extras: Print Post   Remind Me!   Notify Moderator  
Sarkikos
Postmaster
*****

Reged: 12/18/07

Loc: Scotophobe Maryland, USA
Re: Thermal Issues and Fans Successes new [Re: Tom and Beth]
      #5600829 - 01/02/13 08:09 AM

Quote:

Quote:

So, I just discovered that the bigger the cell, the more current it holds. Those big "D" cells would be a lot better than the 8 "AA" batteries I am using! I'm thinking that a Lithium battery that adds up to 12 volts or NiMH would be even better than Alkaline and last even longer.



I didn't read the whole thread, so if these are covered already, forgive me

You could put a rechargeable 12V battery in the rocker. 7AH to 18AH, for example, doesn't take up much space. the 7AH size makes a good counterweight.




I have a large capacity 12v battery that I use exclusively for dew control. Dew is huge in my area. The 12v battery needs to be recharged after every night at the dark site. I keep this battery along with the dew controller in a metal basket I hang from the front of the Dob mount. (No rocker box here.)

A separate power supply - the Orion 8-pack of D cells - powers the fan. I need to replace a D cell about every year or so. This power supply is in a little case that hangs from a side of the Dob mount.

This dual setup works great for me. I've never had either of these battery supplies fail me over the course of a five or six hour observing session.

Mike


Post Extras: Print Post   Remind Me!   Notify Moderator  
Sarkikos
Postmaster
*****

Reged: 12/18/07

Loc: Scotophobe Maryland, USA
Re: Thermal Issues and Fans Successes new [Re: Tom and Beth]
      #5600831 - 01/02/13 08:11 AM

Quote:

As for the fan speed control: I control the speed using a potentiometer within reach of the Ep. Since I built it, I see these units meant for computers where the entire circuit board is already built, and cost 5 bucks.




I've never had any speed control for fans. Where can I order one of these circuit boards and how would I set it up?


Mike


Post Extras: Print Post   Remind Me!   Notify Moderator  
Sarkikos
Postmaster
*****

Reged: 12/18/07

Loc: Scotophobe Maryland, USA
Re: Thermal Issues and Fans Successes new [Re: azure1961p]
      #5600834 - 01/02/13 08:18 AM

Pete,

Quote:

Just make sure a full 1" of the three inch fan is BELOW the mirrors reflected surface. Essentially so the bottom 1" of the fan is blowing the the side of the mirror. This forces the remaining two inches above the mirrors surface to powerfly blow the boundary layer off. If you have the tip of the 3" hole just above the mirrors surface it's a wasted exercise as the ai blows clean over the boundary layer doing nothing at all. You'd think it was close enough like the cyclonic wind off the fan would disrupt it anyway or at least partially. It did NOTHING. You need a third of the fan blowing on the side of the primary but believe me this works Wonderfully.




Placing a third of the fan below the edge of the mirror would also help cool the mirror as well as disrupt the boundary layer. I like it when improvements perform more than one function.

But here's a question from an experienced amateur astronomer but a newbie handyman craftsman: How did you cut the 3" hole in the side of the OTA? I don't understand why no one has asked this. Do most folks have a lot of prior experience cutting big holes in the side of metal tubes? I don't get this... I never had metal shop in high school.

Mike


Post Extras: Print Post   Remind Me!   Notify Moderator  
Starman1
Vendor (EyepiecesEtc.com)
*****

Reged: 06/24/03

Loc: Los Angeles
Re: Thermal Issues and Fans Successes new [Re: Sarkikos]
      #5601031 - 01/02/13 10:59 AM

Mike,
You can use what they call a "hole saw". It's like a cup with teeth on the rim and it attaches to a drill. There's a center bit to guide it in straight.
You can get these saws up to fairly large sizes on-line, but most larger hardware centers typically have them up to 3".
I did this to create a focuser hole in a tube I had and it's how carpenters put holes in doors for door handles.


Post Extras: Print Post   Remind Me!   Notify Moderator  
nevy
professor emeritus
*****

Reged: 02/07/12

Loc: UK
Re: Thermal Issues and Fans Successes new [Re: Starman1]
      #5601052 - 01/02/13 11:05 AM

Quote:

Mike,
You can use what they call a "hole saw". It's like a cup with teeth on the rim and it attaches to a drill. There's a center bit to guide it in straight.
You can get these saws up to fairly large sizes on-line, but most larger hardware centers typically have them up to 3".
.

I did this to create a focuser hole in a tube I had and it's how carpenters put holes in doors for door handles.



Be sure to get one that cuts metal as most are designed for cutting wood


Post Extras: Print Post   Remind Me!   Notify Moderator  
Sarkikos
Postmaster
*****

Reged: 12/18/07

Loc: Scotophobe Maryland, USA
Re: Thermal Issues and Fans Successes new [Re: Starman1]
      #5601115 - 01/02/13 11:44 AM

Don,

Quote:

You can use what they call a "hole saw". It's like a cup with teeth on the rim and it attaches to a drill. There's a center bit to guide it in straight.
You can get these saws up to fairly large sizes on-line, but most larger hardware centers typically have them up to 3".
I did this to create a focuser hole in a tube I had and it's how carpenters put holes in doors for door handles.




Thank you. I had seen these, but always thought they were meant for wood, not metal. They have no problem cutting a hole in a metal tube?

Mike


Post Extras: Print Post   Remind Me!   Notify Moderator  
Sarkikos
Postmaster
*****

Reged: 12/18/07

Loc: Scotophobe Maryland, USA
Re: Thermal Issues and Fans Successes [Re: Sarkikos]
      #5601117 - 01/02/13 11:44 AM

Thanks, Nevy, you answered my second question.


Mike


Post Extras: Print Post   Remind Me!   Notify Moderator  
azure1961p
Postmaster
*****

Reged: 01/17/09

Loc: USA
Re: Thermal Issues and Fans Successes [Re: rlmxracer]
      #5601221 - 01/02/13 01:01 PM

Quote:

Thanks for the tips. Did you ever try it without the holes on the opposite side of the tube having the rear fan also blowing up the tube?




Alan Adler did and it was not as effective ad the heat hits the wall of the tube on the other side and basically goes all over the place. It needs a short direct path immediately out.

Pete


Post Extras: Print Post   Remind Me!   Notify Moderator  
Pages: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | >> (show all)


Extra information
13 registered and 20 anonymous users are browsing this forum.

Moderator:  ausastronomer, Phillip Creed, JayinUT, okieav8r 

Print Thread

Forum Permissions
      You cannot start new topics
      You cannot reply to topics
      HTML is disabled
      UBBCode is enabled


Thread views: 20355

Jump to

CN Forums Home


Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics