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My Mini Observatory - Final Version?

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#1 Rac19

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Posted 30 May 2021 - 01:02 AM

I have posted images of this setup over the past six months, as it has evolved, and there might be some who would be interested to see how it has developed.

 

The pier is made from cinder blocks, filled with concrete. There is a "rat cage" made from 2 x 10 mm aluminium plates and 3 x 12 mm bolts, but it is barely visible in this view. The cover is made from 6 mm plywood, 4 mm would probably work and would be lighter than the current 20 kg.

 

It was a real challenge to prevent the hot box effect on summer days. Neither insulation nor reflective cover seemed to work. The temperature would rapidly climb to 55 degrees C on hot days. The only thing that worked was a 12 VDC fan, drawing ambient air from below,  and even then only with a vent in the top of the box. On a 40 degree day, temperature inside stays under 45 degrees.

 

I installed a 12 VDC 100 fan heater to prevent condensation on cold damp winter's nights. To my surprise, it raises the temperature by about 7 Celcius degrees. There are thermostats controlling both fans.

 

So now I have a permanent set up with no need to polar align or star align each session. Start up and shutdown times are just a minute or so.

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Edited by Rac19, 30 May 2021 - 02:52 AM.

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#2 GaryShaw

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Posted 30 May 2021 - 09:16 AM

Hi Rac

 

A very timely post!

 

I’m just starting the process of designing a similar ‘Observatory in a Box’ on my front porch just outside Boston. I’ve given up on my telegizmo cover which allowed heat under the cover to build to 107F in mid May at 42 north latitude. I’ve been looking at both 1) a roll-away enclosure design and 2) a hinged box-top approach similar to the one in the photo below. The hinged approach would help minimize the bulk of the box on the front porch and make domestic life less stressful.

 

You’ve obviously solved all the problems I still face so, could you perhaps comment on this list below of features I’m planning to incorporate in the design? I’m sure I have forgotten something.

 

- A basic box, as pictured below but one side will be curved to work with the shape of the porch and railing. Likely the box will be made from 1/2 - 5/8” plywood. It will be painted gloss white to help reflect heat.

- The top will be operated by hydraulic lifters to make opening it easy and smooth.

- The bottom will be enclosed so warm moist air from below the porch, doesn’t rise inside and raise the risk of dew. There will be a clear space of 1” around the pier which will be an iOptron pier to mate with the CEM70 G mount. The pier will site on a filled concrete block base below the porch.

- An exhaust fan will eject hot air at the top of the box on the ‘sun side’ with intake vents on the bottom of the shade side. Vents will have insect screens. 

- Heating rods will help maintain winter temperature above 32 inside the box. Temperature and humidity sensors will control the on/off status of the ventilation fan and heating rods. I hope we can keep winter temperature above 32F and summer temperature below 90F. The specifications for scope, mount cameras want temperatures kept in a range of 23-114F. 

- We’ll bring a power line from the house to support the heating and venting components as well as to power the mount and run the Intel Nuc computer that runs all my observing gear. 
 

That’s a summary of where I am so far. I still need to finalize the size, exact shape and all the materials and components … so your thoughts on the list would be helpful. My scope is a 203 mm F4 Newtonian so I have to establish a ‘park position’ that has the scope horizontal to minimize the height of the box. 
 

Thanks very much for posting your observatory. If there are any additional photos that show more of the details or explain what the ‘rat cage’ is, it would be great to see them.

 

Congratulations and Clear Skies…

Gary 

 

 

78C2CE20-1308-42AA-895A-E3C0199A9AA2.jpeg

 

 



#3 Rac19

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Posted 30 May 2021 - 05:44 PM

Hi Gary,

 

I am happy to help where I can.

 

I get ambient temperatures of 107 F. Inside the box it was getting to be over 50 C (122 F), which really was a cause for concern, mainly due to the possibility of grease running and contaminating the optics. I was also concerned about humidity building up under a plastic cover under summer conditions.

 

I think that good ventilation is the key for limiting temperature rise. It keeps the inside temperature to a few degrees above ambient. I needed both a fan and a vent so that air is fully exchanged inside the box. My guess is that I am getting 4 air changes a minute. I have the fan at the bottom and the vent at the top but the reverse would work too. Insulation and a reflective cover didn't seem to make much difference.

 

My box it made from 6 mm (1/4") plywood and weighs 20 kg (45 lbs). I think that 1/2" plywood would be quite heavy.

 

I think that 3 or 4 hinges are necessary. If there are only 2 and one of them comes loose while tipping the cover, there could be damage to the 'scope.

 

I am using an NUC too, by the way and find it very satisfactory.

 

The first image below shows the bare pier and "rat cage" (the aluminium plates and levelling screws). These basic structural elements remain, they are just hidden.

 

The second images shows another view.

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Edited by Rac19, 30 May 2021 - 06:05 PM.

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#4 jcj380

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Posted 31 May 2021 - 05:38 AM

A trick campers use to reduce heat from direct sun is to rig an awning over their tent or trailer. I’ve wondered if adding a sheet of something lightweight to the top of a scope hotel using stand-off bolts would help keep the inside temp down. Just a thought.
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#5 Rac19

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Posted 31 May 2021 - 05:56 AM

A trick campers use to reduce heat from direct sun is to rig an awning over their tent or trailer. I’ve wondered if adding a sheet of something lightweight to the top of a scope hotel using stand-off bolts would help keep the inside temp down. Just a thought.

Thanks for suggestion. I have a solar reflective cover that seemed not to be effective when I used it. As you suggest, setting it up as a fly sheet (no contact with the cover) would be more effective. I must say though that adequate ventilation got it through some pretty hot days during our southern hemisphere summer.



#6 astrohamp

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Posted 31 May 2021 - 08:49 AM

The 'parasol' worked for SkyLab.

 

I've been working on a housing to use an automotive flat air filter to reduce dust and bug infiltration from the vent fan.

 

Likewise trying to find a small enough circular filter to fit over my newtonian mirror fan as well.


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#7 Rac19

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Posted 31 May 2021 - 04:42 PM

The 'parasol' worked for SkyLab.

 

I've been working on a housing to use an automotive flat air filter to reduce dust and bug infiltration from the vent fan.

 

Likewise trying to find a small enough circular filter to fit over my newtonian mirror fan as well.

I considered using a "market" umbrella to ward off the summer sun.

 

I am interested in your suggestion of an air filter. The high air exchange rate brings with it more airborne contaminants. There is a thermostat, set at 30 Deg C, so that the operation hours of the fan are reduced.


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#8 tommyboy

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Posted 03 June 2021 - 09:00 AM

What do you guys do about ambient light pollution? Do your neighbors not light their yards?



#9 astrohamp

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Posted 03 June 2021 - 01:39 PM

I just haven't taken the time to scout out or rummage for a suitable housing with a big enough pleated filter.  Something that can be wall mounted and easy to replace filter elements.  It is out there, just needs to be moved up the project list.



#10 Rac19

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Posted 03 June 2021 - 03:05 PM

What do you guys do about ambient light pollution? Do your neighbors not light their yards?

Neighbour's lights can be a problem, intermittently, but not too bad. I do wonder a about local glow from street lights. They are concealed by the house, but there could be sine effect. There is a single light in the next street (behind my house) that is actually in view. Hopefully the dew shield reduces in effect.



#11 Rac19

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Posted 03 June 2021 - 03:10 PM

I just haven't taken the time to scout out or rummage for a suitable housing with a big enough pleated filter.  Something that can be wall mounted and easy to replace filter elements.  It is out there, just needs to be moved up the project list.

I have a clear mental image of a suitable housing so maybe I have seen one, sometime in the past. Then again, maybe I am dreaming because I can't find one in web searchesmad.gif.


Edited by Rac19, 03 June 2021 - 03:10 PM.


#12 garblivet

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Posted 06 June 2021 - 04:02 AM

May be able to get a small steel plate with the center cut out and mount it around the intake.  Then get a house AC filter and cut the material to size (you'll have plenty of replacement material) and attach to the steel plate with magnets.  My only concern would be how the filter handles being outside.  I'm in the planning stages for a scope motel.  Thinking of using a small solar fan for the exhaust on the upper side opposite an intake on the bottom, like yours, and a hood to keep the rain out.  Also 2 Eva-Dry E-500s for moisture.



#13 Rac19

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Posted 06 June 2021 - 05:42 AM

I am picturing a simple wooden frame, maybe 6" or 8 " square, to fit a pleated square filter. It would be screwed to the underside of plywood floor, so exposure to the elements would not be an issue. My only problem is the translation from imagination to reality.

 

I have my fan drawing air from under the floor, where I hope to house the filter, with a simple passive vent high on one of the walls. The advantage of this is the the floor is the one part of the housing that doesn't move.



#14 jcj380

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Posted 06 June 2021 - 09:23 AM

I considered using a "market" umbrella to ward off the summer sun.

waytogo.gif   Even better - no engineering required!



#15 Cfreerksen

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Posted 06 June 2021 - 03:22 PM

I am picturing a simple wooden frame, maybe 6" or 8 " square, to fit a pleated square filter. It would be screwed to the underside of plywood floor, so exposure to the elements would not be an issue. My only problem is the translation from imagination to reality.

 

I have my fan drawing air from under the floor, where I hope to house the filter, with a simple passive vent high on one of the walls. The advantage of this is the the floor is the one part of the housing that doesn't move.

Like this? https://www.cloudyni...-run/?p=9663230

I got it from amazon. https://www.amazon.c...e?ie=UTF8&psc=1

 

Chris


Edited by Cfreerksen, 06 June 2021 - 03:24 PM.


#16 garblivet

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Posted 06 June 2021 - 05:36 PM

I am picturing a simple wooden frame, maybe 6" or 8 " square, to fit a pleated square filter. It would be screwed to the underside of plywood floor, so exposure to the elements would not be an issue. My only problem is the translation from imagination to reality.

 

I have my fan drawing air from under the floor, where I hope to house the filter, with a simple passive vent high on one of the walls. The advantage of this is the the floor is the one part of the housing that doesn't move.

The location of your fan makes sense, being powered.  Less stuff to mess with just to take the box off.  And next to the heater to circulate the warm air and keep the condensation at bay.  I was thinking of going solar to not have to disconnect anything (read: be lazy), though these little systems are probably less reliable.  My thoughts on the fan being higher and opposite the intake is air flow through the box and over the equipment, and removing the higher/warmer air, thus hopefully keeping everything a little cooler.  That's the theory anyway... My box would need to be taller, having a newt pushing the mount (and counterweight shaft) limits and not wanting to park horizontally. This thread's been a big help, btw. Thanks!



#17 Rac19

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Posted 06 June 2021 - 06:02 PM

The 200 Watt fan heater has been a surprise. I just had a look this morning, the ambient temperature is 9 degrees C and inside the box it is 16 degrees C. That's definitely enough temperature rise to prevent condensation.

 

By the way, the reason I used 6 mm plywood rather than foam board, which would have been much lighter, is that we get large hail (tennis ball size) occasionally.

 

I am appy to help. I have found CN to be a rich source of helpful advice over the years and I am happy to make a contribution.



#18 garblivet

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Posted 06 June 2021 - 07:50 PM

Yeah, I would have gone with the thicker wood (and tank armor) as well.  grin.gif  I'm on the Florida Panhandle coast.  No hail for me.  Just rain/humidity/high UV.  Everything comes inside for those pesky hurricanes.  I wasn't planning on using a heat source, but definitely will now. 

 

I, like pretty much everyone here, have learned quite a bit from this forum.  It's made my learning curve with this hobby easier to deal with... well... most of the time.  Haha.




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