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azure1961p
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Reged: 01/17/09

Loc: USA
Re: Thermal Issues and Fans Successes new [Re: rlmxracer]
      #5601922 - 01/02/13 08:38 PM

I'm giving the thumbs down on RadioShack. They used to be good. A dedicated electronic component supplier would be far better. I found a great place locally but had I not it'd been an online purchase.

Pete


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azure1961p
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Reged: 01/17/09

Loc: USA
Re: Thermal Issues and Fans Successes new [Re: rlmxracer]
      #5601928 - 01/02/13 08:41 PM

Oh shrink tubing: black rubber tubi g that shrinks around wire insulating it when a heat gun blows hot air on it. A hair dryer will do in a pinch if your diligent. Oh... Advice at RadioShack???? Forget it. At least locally these guys didn't even kno what the hell a potentiometer was!!!! I'm serous. They sell cell phones and at screen cables, GPS and assorted junk these days.

Pete


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rlmxracer
sage
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Reged: 11/09/11

Loc: Motocross Mecca , CA
Re: Thermal Issues and Fans Successes new [Re: azure1961p]
      #5601944 - 01/02/13 08:51 PM

I'd have to concur RadioShack has been slipping for quite a while. I have ordered from Mouser electronics with good luck. They seem to have everything.

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Scanning4Comets
Markus
*****

Reged: 12/26/04

Loc: Ontario, Canada
Re: Thermal Issues and Fans Successes new [Re: rlmxracer]
      #5602252 - 01/03/13 01:06 AM Attachment (18 downloads)

I recall reading an extensive article by Brian Greer and it had videos attached showing that the boundary layer will hug the face of the mirror ALL NIGHT....

http://www.fpi-protostar.com/bgreer/fanselect.htm

Notice in the article link I just posted, front fans are needed on mirrors that are THICKER and it also depends on your area as to how fast temperatures change. As I stated, my mirror is just over an inch thick, so I think the rear fan I have with the baffle is sufficient.

One thing I'd like to mention is that I am using speaker wire for the connections....would that have any effect on battery life? or does it not matter? I also need batteries that last longer and I think I will go for 8 "D" cell batteries instead of using the 8 "AA" batteries I was using.

Cheers,


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rlmxracer
sage
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Reged: 11/09/11

Loc: Motocross Mecca , CA
Re: Thermal Issues and Fans Successes new [Re: Scanning4Comets]
      #5602299 - 01/03/13 02:17 AM

Quote:

I recall reading an extensive article by Brian Greer and it had videos attached showing that the boundary layer will hug the face of the mirror ALL NIGHT....

http://www.fpi-protostar.com/bgreer/fanselect.htm

Notice in the article link I just posted, front fans are needed on mirrors that are THICKER and it also depends on your area as to how fast temperatures change. As I stated, my mirror is just over an inch thick, so I think the rear fan I have with the baffle is sufficient.

One thing I'd like to mention is that I am using speaker wire for the connections....would that have any effect on battery life? or does it not matter? I also need batteries that last longer and I think I will go for 8 "D" cell batteries instead of using the 8 "AA" batteries I was using.

Cheers,



The speaker wire is fine. These fans only draw .1 amp or so. The 120mm Silenex fan I just got only draws .09amp. Mouser electronics has several variations of 8 D cell battery holders.

Edited by rlmxracer (01/03/13 02:22 AM)


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demiles
professor emeritus
*****

Reged: 11/07/06

Re: Thermal Issues and Fans Successes new [Re: azure1961p]
      #5602385 - 01/03/13 05:41 AM

I'm not saying you can't get a decent image, but over coming a 40 degree differential with continuing dropping temps in 40 minutes? I'm not sure that's even possible.

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Scanning4Comets
Markus
*****

Reged: 12/26/04

Loc: Ontario, Canada
Re: Thermal Issues and Fans Successes new [Re: demiles]
      #5602424 - 01/03/13 06:57 AM

Yea,

I just talked to a good friend on the phone and I'm going to switch to 8 D cell batteries and run my fan on those.....Should last a lot longer than 2 or 3 nights of observing, LOL!

If you guys wanna drill holes in your telescope tubes, or add boundary layer fans for a 1" mirror, all the power to you.....but for a 1" mirror it is not needed. I'm sticking with what I currently have now because I am getting excellent views the way things are.

Cheers,


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Bob S.
Carpal Tunnel
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Reged: 07/14/05

Re: Thermal Issues and Fans Successes new [Re: Scanning4Comets]
      #5602434 - 01/03/13 07:04 AM

Quote:

Yea,

I just talked to a good friend on the phone and I'm going to switch to 8 D cell batteries and run my fan on those.....Should last a lot longer than 2 or 3 nights of observing, LOL!

If you guys wanna drill holes in your telescope tubes for a 1" mirror, all the power to you.....but for a 1" mirror it is not needed.

Cheers,




Markus, I hate to challenge folks but how did you arrive at such a firm conclusion about 1" thick mirrors? A friend recently had Zambuto make him a 1" thick 10" f/6 mirror that he placed in an older Starmaster structure. He drilled 3 large holes in his mirror box just above the primary mirror with a fan blowing from behind the mirror and the views we had through it down at Chiefland, Florida a few months ago were some of the finest I have ever seen. I was amazed at the contrast and the rock steady views we were getting with his modified setup. Bob


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azure1961p
Postmaster
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Reged: 01/17/09

Loc: USA
Re: Thermal Issues and Fans Successes new [Re: demiles]
      #5602555 - 01/03/13 08:56 AM

Quote:

I'm not saying you can't get a decent image, but over coming a 40 degree differential with continuing dropping temps in 40 minutes? I'm not sure that's even possible.




Maybe with a big mirror its problematic but I routinely have drops in temp from inside and out down to ten degrees from 70f - after an hour cool down its good to go. Kinda simple really but my mirrors just 8" .

Pete


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Scanning4Comets
Markus
*****

Reged: 12/26/04

Loc: Ontario, Canada
Re: Thermal Issues and Fans Successes new [Re: Bob S.]
      #5602557 - 01/03/13 08:56 AM

Quote:

Markus, I hate to challenge folks but how did you arrive at such a firm conclusion about 1" thick mirrors? A friend recently had Zambuto make him a 1" thick 10" f/6 mirror that he placed in an older Starmaster structure. He drilled 3 large holes in his mirror box just above the primary mirror with a fan blowing from behind the mirror and the views we had through it down at Chiefland, Florida a few months ago were some of the finest I have ever seen. I was amazed at the contrast and the rock steady views we were getting with his modified setup. Bob




http://www.fpi-protostar.com/bgreer/fanselect.htm

Good for you Bob, I think that's awesome. I have had rock steady views with no fan and just the back of the mirror exposed. Scroll 3/4 of the way down and you can read it for yourself, (Front-blowing fans). I guess I was referring to front boundary layer fan. Brian Greer says that a fan on the back of a mirror an inch thick, (or just over that as my mirror is 1 1/8"), is sufficient.

Cheers,


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demiles
professor emeritus
*****

Reged: 11/07/06

Re: Thermal Issues and Fans Successes new [Re: azure1961p]
      #5602570 - 01/03/13 09:08 AM

I had a Parks 6 in. F8 and I would say it's almost impossible to over come that kind of differential in such a short time. Glass will only dissipate heat so fast, even with fans running.

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azure1961p
Postmaster
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Reged: 01/17/09

Loc: USA
Re: Thermal Issues and Fans Successes new [Re: Scanning4Comets]
      #5602573 - 01/03/13 09:13 AM

Well that's the difference between reading about someone else's experience and seeing for yourself. The boundary layer fan isn't needed if you're "scanning for comets" but dust storms on mars for example is another matter. The idea of running no fan at all even if the aperture is 4" is just terrible. Again if all your looking at are low power views of fuzzy comets u can get away with it.

It's not a debating point. Either you get rid of your thermals and see more detail or you don't and u see less. It's one or the other. If you use primarily low power you don't need it but your stars are still going to flare.

Pete

Edited by azure1961p (01/03/13 09:14 AM)


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azure1961p
Postmaster
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Reged: 01/17/09

Loc: USA
Re: Thermal Issues and Fans Successes new [Re: demiles]
      #5602579 - 01/03/13 09:17 AM

Quote:

I had a Parks 6 in. F8 and I would say it's almost impossible to over come that kind of differential in such a short time. Glass will only dissipate heat so fast, even with fans running.




Ill post pics of my setup maybe I've overlooked something. The heat never truly leaves the tube 100% but what residual percent is left does a nifty a nifty job of keeping my secondary dew free.

Pete


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Bob S.
Carpal Tunnel
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Reged: 07/14/05

Re: Thermal Issues and Fans Successes new [Re: Scanning4Comets]
      #5602589 - 01/03/13 09:25 AM

Quote:

Quote:

Markus, I hate to challenge folks but how did you arrive at such a firm conclusion about 1" thick mirrors? A friend recently had Zambuto make him a 1" thick 10" f/6 mirror that he placed in an older Starmaster structure. He drilled 3 large holes in his mirror box just above the primary mirror with a fan blowing from behind the mirror and the views we had through it down at Chiefland, Florida a few months ago were some of the finest I have ever seen. I was amazed at the contrast and the rock steady views we were getting with his modified setup. Bob




http://www.fpi-protostar.com/bgreer/fanselect.htm

Good for you Bob, I think that's awesome. I have had rock steady views with no fan and just the back of the mirror exposed. Scroll 3/4 of the way down and you can read it for yourself, (Front-blowing fans). I guess I was referring to front boundary layer fan. Brian Greer says that a fan on the back of a mirror an inch thick, (or just over that as my mirror is 1 1/8"), is sufficient.

Cheers,




Markus, As a point of reference, I have owned more non-fan Starmasters than anybody in the country/world and was not a big believer in fans. I had tried a fan strategy from a great guy out in California that was making elegant fan retrokits for Starmasters and unfortunately did not see any clear evidence from that approach to improved views at the time. However, when I saw how Joe Wambo's 32" f/3.7 scope performed in the Florida Keys, I was totally blown away. He attributes his incredible views to the additive benefits of a frontal surface blowing fan. We saw more detail on Mars than any of us experienced observers had ever seen at 950x. I then had a conversation with Jimmy Lowery of Texas with his 48" f/4 and he says that he never views without running his 10 MagLev fans in the enclosed mirror box and says it really cleans up his DSO work.

I know that we are comparing watermellons to grapes with the sizes you are mentioning but my preliminary tests on my 20" f/3 Lockwood/JP Astrocraft with front blowing and rear sucking fans seems to be bearing incredible fruit in terms of resolving abilities. I have read Brian's missive on mirrors that was recently put up and his early work with cooling and until recently, was not a convert. However, after seeing and hearing such glowing reports, I decided to create with John Pratte what we call a Comprehensive Boundary Layer Mitigation System (CBLMS). The complete system seems to be additive. However, have not had very many nights with the new system and will need many months of testing before I can sort out and try and control all the variables I am interested in.

I am delighted that this subject about boundary layers is resurfacing. It may prove to have more benefits than we may have realized? Cannot really say for sure at this point?

Bob

Edited by Bob S. (01/03/13 09:34 AM)


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Dick Jacobson
scholastic sledgehammer


Reged: 12/22/06

Loc: Plymouth, Minnesota, USA
Re: Thermal Issues and Fans Successes new [Re: Sarkikos]
      #5602598 - 01/03/13 09:32 AM

Quote:

Dick,

Quote:

Quote:

Has anyone else drilled vent holes at the primary without using an opposing fan?



Several years ago I tried drilling a ring of vent holes even with the mirror surface, without using a fan. It did not seem to have any significant effect. This was a 10" mirror in a solid tube.

If you want to get rid of the boundary layer, I believe it is best to have the mirror totally out in the open, as in my post Naked Mirrors.




Well, I'm not doing anything like that to my 10" solid-tube Dob! As mentioned in the thread, this would also leave the mirror exposed to dewing. The dew in my area is substantial. I need to have dew strips at eyepiece, the finder eyepiece and my Telrad or they will dew quickly. I can't imagine having a completely exposed mirror in this neck of the woods. Not gonna' happen' here! I'd have to completely encircle the primary with a dew strip. What would that do to the thermal issues?

I think I'll continue to experiment with other solutions, including venting and scrubbing the boundary layer with a fan.


Mike



I have not had any problems with dew on my "naked mirror" even though I have a lot of dew/frost problems on eyepieces and secondary mirrors. The difference is that the primary mirror is extremely thick (2-5/16" in my case) and it is nearly impossible for it to cool down below the dewpoint.

The mirror seems to give better images when it is out in the open than it ever did when it was in a tube. With the front fan off, I can still sometimes see a turbulent boundary layer when looking at a bright defocused star, so I think a boundary-layer fan is needed when your mirror is more than a few degrees warmer than the air.


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JasonBurry
sage


Reged: 04/27/12

Loc: Cape Spencer, NB, Canada
Re: Thermal Issues and Fans Successes new [Re: azure1961p]
      #5602602 - 01/03/13 09:36 AM

I added a boundary layer fan and speed control, along with secondary dew heating to my 8" truss dob this fall. I've been observing with this instrument for the best part of 10 years.

The difference in performance was immediate and obvious.

My setup is simple. My mirror (8", F6, about 1.25" thick) is passively cooled on the back side, no fan there (yet). Just some mighty holes in the 3 point mirror cell to speed things a touch. I may add a small fan to improve slightly, but right now it's happily loosing 20C in about 1.5 hours.

My fan is for boundary layer control. It's an old computer "ISA slot cooler", a thin squirrelcage style blower. It's fed thru a POT from a 2000mah 8.4V NiMH pack mounted in the mirror cell. The pack also powers the dew heater and the red dot finder, giving about 12 hours endurance for the fan at full speed, or 6 hours with both fan and heat (though I only use the heat in "defog" mode).

I created a plastic louvre on the fan's outlet to distribute the flow across the mirror face. Observing the clearing of condensation from the mirror with the fan running after a session allowed me to tweak the louvre to optimize the airflow as best I could. The pot allows the fan to run down to double-digit RPM's, and I usually run it at about 1/3rd speed during observing. It's velcro mounted to the mirror box, and causes no observable vibration.







The fan installation really helped in seeing fine detail in Jupiter, festoons and detail galore, indeed views I'd thougth impossible with this scope. The Jovian moons have become miniscule worlds unto themselves. Fine galactic detail has improved. Now if only my skies would.... LOL.

J


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Sarkikos
Postmaster
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Reged: 12/18/07

Loc: Scotophobe Maryland, USA
Re: Thermal Issues and Fans Successes new [Re: azure1961p]
      #5602604 - 01/03/13 09:38 AM

Pete,

Quote:

Well that's the difference between reading about someone else's experience and seeing for yourself. The boundary layer fan isn't needed if you're "scanning for comets" but dust storms on mars for example is another matter. The idea of running no fan at all even if the aperture is 4" is just terrible. Again if all your looking at are low power views of fuzzy comets u can get away with it.

It's not a debating point. Either you get rid of your thermals and see more detail or you don't and u see less. It's one or the other. If you use primarily low power you don't need it but your stars are still going to flare.




I have a 6" f/5 Dob, 5" f/5 Dob, a 4.5" f/4.4 Ball Scope, and a 3" f/4 Hand-Held Newt. I haven't bothered to put fans in any of them yet. But I mostly use them for deep sky or grab-n-go. Sometimes the 5" goes with me to my dark site instead of the 10" when I bring the family and want more room in the car. It does fine without a fan, but then I'm not trying to tease out fine detail on bright planets at the dark site.

On the other hand, I do take out that 5" at my house for lunar observation. It might be a good idea to rig a fan up to the bottom of the primary.

Mike


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Sarkikos
Postmaster
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Reged: 12/18/07

Loc: Scotophobe Maryland, USA
Re: Thermal Issues and Fans Successes new [Re: Scanning4Comets]
      #5602620 - 01/03/13 09:48 AM

Mark,

Quote:

I just talked to a good friend on the phone and I'm going to switch to 8 D cell batteries and run my fan on those.....Should last a lot longer than 2 or 3 nights of observing, LOL!




Yep, you should be able to go about a year or so without having to replace any of the D cells. Don't even bother getting rechargeable D's.

I have a hand-held battery charge checker that I check all my batteries with before I go to my dark site. It's a bother to take the eight D cells out and check them, because I know that they'll seldom show a low charge. I take extra D cells with me just in case, too, but I don't think I've ever had to replace any of the D's in the field.

Mike


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Starman1
Vendor (EyepiecesEtc.com)
*****

Reged: 06/24/03

Loc: Los Angeles
Re: Thermal Issues and Fans Successes [Re: Sarkikos]
      #5602641 - 01/03/13 10:00 AM

Download this free calculator:
http://www.cruxis.com/scope/mirrorcooling.htm
You can enter the data for your mirror and fans and see how effective active cooling is.
With the fans in my scope, and my 1.25" thick 12.5" mirror, I can overcome a 40 degree differential in temperature in around 30 minutes (mirror is then within 1 degree C of ambient).
So, fast cooling of glass is possible, but only with high capacity fans doing the job.
If you play with the calculator, you'll see that normal radiative cooling isn't adequate for any mirror in a falling temperature environment.


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Scanning4Comets
Markus
*****

Reged: 12/26/04

Loc: Ontario, Canada
Re: Thermal Issues and Fans Successes [Re: Starman1]
      #5602706 - 01/03/13 10:41 AM

Quote:

Well that's the difference between reading about someone else's experience and seeing for yourself. The boundary layer fan isn't needed if you're "scanning for comets" but dust storms on mars for example is another matter. The idea of running no fan at all even if the aperture is 4" is just terrible. Again if all your looking at are low power views of fuzzy comets u can get away with it.

It's not a debating point. Either you get rid of your thermals and see more detail or you don't and u see less. It's one or the other. If you use primarily low power you don't need it but your stars are still going to flare.

Pete




I have to respectfully disagree here Pete. I am talking from experience here. My last quote was just showing something about the boundary layer fan in an article.

I have been observing since I was 19 and I am 50 now. Back when I got my first 10" F/5.6 plate glass mirror telescope I had incredible views of Jupiter and other planets as well. I had no fans on the back, nothing. It's not a matter of "if you're just scanning for comets" here either. I have had my telescope up to 488x and the views were excellent, which is pretty rare in my neck of the woods. It IS a debating point and you haven't seen what I have seen in my telescope as you were not here when I saw what I did.

I'm not saying boundary layer fans or fans at the back of telescopes is useless at all because I have a large 12cm fan on the back of the mirror now. All I was saying was that I have seen incredibly sharp detail on the planets and had my scope up at relatively high powers and I do NOT have a boundary layer fan.

It appears that going with a boundary layer fan even with my 10" scope and smaller is the way to go from what I just read....so now I will be looking into making that happen on my scope seeing as testimonials outweigh not having a boundary layer fan.

This should prove interesting below...

http://www.cloudynights.com/ubbarchive/showflat.php/Cat/0/Number/342304/page/...



Cheers,


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