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Equipment Discussions >> Reflectors

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Bob S.
Carpal Tunnel
*****

Reged: 07/14/05

Re: Thermal Issues and Fans Successes new [Re: azure1961p]
      #5603714 - 01/03/13 09:26 PM

Quote:

Quote:

Quote:

Quote:

However, there appears to be a small body of evidence to suggest that fans properly placed may have some beneficial results that might not be comparable to a non-fan situation?

Bob




A small body of evidence? How big does it need to be?

Pete




I don't know the answer to that one Pete. If you do, by all means share your wisdom/experience. Results with various cooling strategies have been somewhat equivocal by people in different locales and with different Newts. If they were a sure bet, wouldn't you think that everybody would be using fans and be reporting perfect views? Well, the data is not much clearer than mud at this point, IMO. Maybe we will be able to understand the most important variables? I sure hope so and have set out on a journey of discovery recently to see if a combination of cooling factors results in generally overall improved performance. I frankly cannot predict the outcomes. If I could, I wouldn't be wasting my time here. I would just go buy a Powerball ticket and be done with it


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Tom and Beth
Post Laureate


Reged: 01/08/07

Loc: Tucson, AZ
Re: Thermal Issues and Fans Successes new [Re: Sarkikos]
      #5603841 - 01/03/13 10:53 PM

Quote:

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




http://www.newegg.com/Product/Product.aspx?Item=N82E16835118217

This one controls 2 fans.


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Starman1
Vendor (EyepiecesEtc.com)
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Reged: 06/24/03

Loc: Los Angeles
Re: Thermal Issues and Fans Successes new [Re: demiles]
      #5603919 - 01/04/13 12:00 AM

Quote:

Don, I have that program on my laptop, but the issue with it is its based on one dimension. Thickness. While testing with my Parks 6 in F/8 and then with a Discovery 10 F/6 with a 2 in. thick mirror I couldn't come close to the cool down times that program gave me. I had a fan that I would hang up on the top end of the tube and blow into it for cool down prior to viewing as well as one blowing on the back. The single best thing I've found to do is to move the scope to get close to ambient prior to viewing. For instance I'm going out tonight, so at 5:30 AM this morning I put my mirror box outside in my truck, temps here are going to top out at about 32 degrees so by 5:00 PM its gonna be pretty close to 32. Don't get me wrong I run a back and front too and they help but they themselves have never been able to over come high temperature differentials at the eyepiece.If I were to make a rough guestimate I'd say getting within 10 degrees of ambient has worked well for me.



The issue isn't the thickness of your mirror, but the program's assumption of linear cool down of the night air when you enter beginning and ending temperatures.
Where I observe, the temperature can drop 30 degrees in the first 2 hours, followed by 1 degree per hour.
The mirror is hopelessly warmer than the ambient temperature until the temperature stops falling rapidly. Though the calculator says it should take only 20 minutes to bring my thin mirror to ambient, it often takes more than an hour to as much as two hours. Fans can only do so much.


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nevy
professor emeritus
*****

Reged: 02/07/12

Loc: UK
Re: Thermal Issues and Fans Successes new [Re: Quest]
      #5603920 - 01/04/13 12:01 AM

Quote:

Love this thread! With all the talk about fans blowing air this way and that, I see little, if anything, mentioned about filtration. I don't yet have a fan on my 8" closed tube but I'm concerned about drawing in dirty air - especially during the summer when it doesn't rain often and dirt is easily kicked up by just walking around. If it was an open truss design, I would think the air would adequately dissipate but is there any concern about dust and other particulates accumulating inside a closed tube telescope? I'm a little concerned to install a fan on the back of my telescope without a filter on the intake side and a decent baffle. Perhaps my concerns are unwarranted?




Won't a filter on the fan decrease the airflow and make the fan motor work harder and also make it slightly noisier?

Edited by nevy (01/04/13 12:03 AM)


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FineArt
member


Reged: 01/26/12

Re: Thermal Issues and Fans Successes new [Re: nevy]
      #5604027 - 01/04/13 02:58 AM

This is the fan.

http://video.canadiantire.ca/liveclicker/fb/?ref=aHR0cDovL3d3dy5jYW5hZGlhbnRp...

Edited by FineArt (01/04/13 03:00 AM)


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Sarkikos
Postmaster
*****

Reged: 12/18/07

Loc: Suburban Maryland, USA
Re: Thermal Issues and Fans Successes new [Re: Tom and Beth]
      #5604163 - 01/04/13 07:09 AM

Quote:

http://www.newegg.com/Product/Product.aspx?Item=N82E16835118217

This one controls 2 fans.




Nice. Not very expensive either. They could be attached with Velcro to the OTA or Dob mount. I'd rather go with something like this than try rigging up my own pots.

The only concern for me would be finding adapters for the power supply and fans, or cutting and splicing to the leads I already have. Some folks seem to be able to do this in their sleep. I don't have much prior experience, so I have to figure it out step by step.

Mike


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yowser
member
*****

Reged: 09/14/08

Re: Thermal Issues and Fans Successes new [Re: Starman1]
      #5604263 - 01/04/13 08:47 AM

Quote:

...It's not just heat removal that fans provide--it's also the ability to dispose of the boundary layer in front of the mirror. And while side fans blowing on the mirror certainly do all this a lot faster, they weren't necessary on his 12.5" scope.
--Jim

Commercial scopes are rarely built with as large a clearance between mirror and tube, so the effects of air flow *may* be more visible in the image. ...




I'd be interested to know just how much clearance is acceptable between the mirror and tube in relation to air currents. The reason I ask is that I added a rear fan to an 8" f/4 reflector and also flocked the tube with Protostar flockboard, but also placed 1/4" thick ribs between the tube and flockboard to essentially provide a "thermal window pane" affect. But by doing this, it reduced the clearance between the mirror and tube.


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Sarkikos
Postmaster
*****

Reged: 12/18/07

Loc: Suburban Maryland, USA
Re: Thermal Issues and Fans Successes new [Re: Sarkikos]
      #5604292 - 01/04/13 08:59 AM

I wonder if I could use my Dew-Not Controller to also vary the speed on fans? This controller has two channels, with two outputs per channel. It is connected to a 12v PowerSonic PS-1270 F2 battery. Now I plug three dew strips into the controller, leaving one output free. If I power a fan - or several fans - on the remaining output, it would share one channel with a dew strip. Not too convenient if I want to vary the fans but not that dew strip.

Dew-Not Dual Channel Controller

Maybe the best gizmo for my projected three-fan setup would be another controller to connect to my eight D-cell power supply. I might be able to get by with one channel one output, since the three fans are on a pre-wired harness. But it'd probably be better to have a separate channel for the boundary-layer fan.

But $119 for a second Dew-Not Controller is more than I want to spend.

Any thoughts?

Mike


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Sarkikos
Postmaster
*****

Reged: 12/18/07

Loc: Suburban Maryland, USA
Re: Thermal Issues and Fans Successes new [Re: Sarkikos]
      #5604353 - 01/04/13 09:19 AM

This version is a little less expensive:

AstroZap Dual Channel Controller $98

Mike


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JasonBurry
sage


Reged: 04/27/12

Loc: Cape Spencer, NB, Canada
Re: Thermal Issues and Fans Successes new [Re: Sarkikos]
      #5604478 - 01/04/13 10:27 AM

I simply controlled the speed of my fan with a potentiometer inline with the fan. Can't remember the resistance value of the POT, but it was in the 25K range, IIRC. A lower value would be better, but it's what I could scrounge that day. Ideally, the pot would have a watt rating similar or greater than the fan's, but mine doesn't. It has been reliable so far.

J


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Project Galileo
scholastic sledgehammer
*****

Reged: 11/14/07

Loc: Jefferson County, Colorado
Re: Thermal Issues and Fans Successes new [Re: JasonBurry]
      #5604610 - 01/04/13 11:38 AM

I sealed up the rear of my LB16...



...added a Mauro Da Lio baffle...



...installed one of these super cool fans as a sucking fan with silicon gaskets and neoprene vibration barriers that doesn't show vibration at any speed or magnification...



...and control fan speed with one of these.



In this picture you can see how hard this fan sucks at 73 cfm. The sides of the shroud are being sucked in against the truss poles with the top cover in place. In the huge space of the LB16's tube it easily turns over the air very rapidly and creates a wonderful laminar flow and very clean image. Just like others have reported it all works almost magically. I don't believe I need a side fan. This single set up works great for the size and thickness of mirror I have. I am now a believer in active cooling and boundary layer removal.



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rlmxracer
sage
*****

Reged: 11/09/11

Loc: Motocross Mecca , CA
Re: Thermal Issues and Fans Successes new [Re: Project Galileo]
      #5604858 - 01/04/13 01:53 PM

Clean looking setup P Galileo. I just made the mistake of looking for the quietest 120mm fan I could find. Well I found out how they got it so quiet... it ony flows 40cfm which is not even close oh well. One good thing I found while removing the stock fan I had to remove my primary. I checked the center spot and it was off center by almost 2mm.
Now I just need a fan that flows more air.


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Bob S.
Carpal Tunnel
*****

Reged: 07/14/05

Re: Thermal Issues and Fans Successes new [Re: rlmxracer]
      #5604935 - 01/04/13 02:38 PM

Very nice installation of that sucking fan on the 16" LB Doc! I think one of the potential advantages to our sucking systems is that we are using a pretty homogeneous body of air taking it in from the top. Someone mentioned to me that mixing different kinds of air for frontal boundary layer fans and rear fans is a potentially less optimal strategy than pulling in the air source for the entire primary mirror from one air mass. Not much data on this but it intuitively makes sense. Bob

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Tom and Beth
Post Laureate


Reged: 01/08/07

Loc: Tucson, AZ
Re: Thermal Issues and Fans Successes new [Re: Sarkikos]
      #5605114 - 01/04/13 04:09 PM

Quote:

Quote:

http://www.newegg.com/Product/Product.aspx?Item=N82E16835118217

This one controls 2 fans.




Nice. Not very expensive either. They could be attached with Velcro to the OTA or Dob mount. I'd rather go with something like this than try rigging up my own pots.

The only concern for me would be finding adapters for the power supply and fans, or cutting and splicing to the leads I already have. Some folks seem to be able to do this in their sleep. I don't have much prior experience, so I have to figure it out step by step.

Mike




If you're using computer fans, they often have a connector, yes? This speed control (and there's literally dozens of them to choose from) will attach using that connector. All that's left then is wiring to the battery (or power supply) and that's usually a positive and negative lead.

Some of these fan controllers are better than others, and one can find them on Ebay, Amazon, Newegg and the like. One could even buy a 5 way unit and also power little lights, for a tripod, or map reader...all it takes is removing the circuit card from a computer bay adapter and drilling holes in your scope.

I owe all this to somebody here on CN who posted a pic of one of these.


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azure1961p
Postmaster
*****

Reged: 01/17/09

Loc: USA
Re: Thermal Issues and Fans Successes new [Re: nevy]
      #5605368 - 01/04/13 06:51 PM

Nevy,

By some percentage sure but in all practical purposes no. These filters are highly cavetized - you can see through them. Perhaps that's the difference, if you can't see thru it its too dense. I wouldn't bother with a rear filter but again at public outtings chicken wire across the back would safe guard from kids unknowingly -- "!!!!"

In your own backyard I think it's a personal call - right now my boundary dies t have the ac filter. I might use simple window screening cut out and mounted over the intake. The rear fan - ill never bother covering lest it's an outreach deal and I haven't done one in a good ten years. I miss it actually.

Pete


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Scanning4Comets
Markus
*****

Reged: 12/26/04

Re: Thermal Issues and Fans Successes new [Re: azure1961p]
      #5605466 - 01/04/13 07:50 PM Attachment (7 downloads)

Quote:

If you're using computer fans, they often have a connector, yes? This speed control (and there's literally dozens of them to choose from) will attach using that connector. All that's left then is wiring to the battery (or power supply) and that's usually a positive and negative lead.

Some of these fan controllers are better than others, and one can find them on Ebay, Amazon, Newegg and the like. One could even buy a 5 way unit and also power little lights, for a tripod, or map reader...all it takes is removing the circuit card from a computer bay adapter and drilling holes in your scope.

I owe all this to somebody here on CN who posted a pic of one of these.




I cannibalized a comp fan with a three way switch on it and have it on the back of my mirror. I used to just have it on elastics over the open mirror, but now have it enclosed.

Note the micro switch for changing between low, medium and high speeds as circled.


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nevy
professor emeritus
*****

Reged: 02/07/12

Loc: UK
Re: Thermal Issues and Fans Successes new [Re: azure1961p]
      #5605495 - 01/04/13 08:12 PM

Quote:

Nevy,

By some percentage sure but in all practical purposes no. These filters are highly cavetized - you can see through them. Perhaps that's the difference, if you can't see thru it its too dense. I wouldn't bother with a rear filter but again at public outtings chicken wire across the back would safe guard from kids unknowingly -- "!!!!"

In your own backyard I think it's a personal call - right now my boundary dies t have the ac filter. I might use simple window screening cut out and mounted over the intake. The rear fan - ill never bother covering lest it's an outreach deal and I haven't done one in a good ten years. I miss it actually.

Pete



Ok , thanks for clarifieing that , I wouldn't use one myself as I find the mirror accumulates a bit of dust from normall use after a few sessions anyway even without the fan running , but I have got one of those metal finger guards on the fan , I know from experience that if a finger was to accidentally touch the fan it won't cut my finger tips off as it would just stop the fan from turning but I would be more worried about bending or distorting one of the blades and causing it to vibrate.


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Sarkikos
Postmaster
*****

Reged: 12/18/07

Loc: Suburban Maryland, USA
Re: Thermal Issues and Fans Successes new [Re: Project Galileo]
      #5606629 - 01/05/13 01:26 PM

Project Galileo,

Quote:

...and control fan speed with one of these.






A picture may be worth a thousand words, but sometimes you need more than just seven words to explain a picture.

What is this thing, what type of connectors does it have on both ends, how do you use it, where do you get it?

Mike


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Sarkikos
Postmaster
*****

Reged: 12/18/07

Loc: Suburban Maryland, USA
Re: Thermal Issues and Fans Successes [Re: Sarkikos]
      #5606645 - 01/05/13 01:38 PM

I see this thread has come to the usual controversy between fans that suck and and fans that blow.


Mike


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nevy
professor emeritus
*****

Reged: 02/07/12

Loc: UK
Re: Thermal Issues and Fans Successes [Re: Sarkikos]
      #5606663 - 01/05/13 01:49 PM

Quote:

Project Galileo,

Quote:

...and control fan speed with one of these.






A picture may be worth a thousand words, but sometimes you need more than just seven words to explain a picture.

What is this thing, what type of connectors does it have on both ends, how do you use it, where do you get it?

Mike



That looks like it could be very usefull as I have two scopes with fans so it could be used on either scope to mess with the fan speeds , it would save the trouble of fitting pots to both scopes , come on spill the beans where do you get such a device :-).


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