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Old 08-08-2020, 05:26 PM
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Hisanori (Hisanori)
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Home-made SCT Cooler

I thought this my little project may be useful to share with others. If succesful, it will be very cost effective. Any suggestions, advices or comments are welcome!

During the last rainy weekend, I made my own SCT cooler for 12 inch Meade SCT. Initially I was looking around the market to buy but surprisingly expensive. It is a simple mechanism. I thought I should be able to build for my own.

Before starting my project I researched whether anyone ever built DIY scope coolers. There were few examples were published but any of them didn’t inspire me. I decided to draw my own conceptual design and came up with dimensions after finding available parts at shops.

I adopted a method to “suck out” air from inside the telescope. Most of commercial versions, like Lymax SCT Cooler, are “blow in” air to inside the telescope. I could not find any pros and cons on different methods. But I found it is easier to build this way because for the “blow in” design (1) I am not sure about a suitable design of the nozzle where the air blow out, (2) I am not sure about a type of dust filters which is effective but also not slowdown airflow too much. If I have a good answer to these, it is not too difficult to modify later anyway.

I went shopping to local Jaycar Electronics and Bunnings to buy all parts. Not many things you need. At Jaycar, I bought 12V DC fan 80mm diameter ($19.95), ABS sealed box 115x90x55mm ($15.95), Cigar lighter plug, and RCA plug / panel socket. At Bunnings I bought 40mm 1M PVC pressure pipe ($8.62), 20mm 1M PVC pressure pipe ($3.98) and 40mm PVC pressure valve socket ($4.30).

It was not too hard to build. It’s all plastic not too hard to make holes. However, you need an exact size of hole-saw for the tube intake air from inside the telescope (20mm PVC pipe with external diameter 27mm). This intake tube is connected to the cavity of the sealed box where the exhaust fan attached. This whole air-intake chamber has to be airtight. Not only make an exact size of the hole but also I used silicon glue to seal the connection of the tube and the box to make airtight.

Another attention was needed on connection where the large tube is secured to the box. The large tube effectively holds up a weight of the box and the fan. I used a 40mm valve socket and cut out screw sections, then installed 6 tapping screws to connect the socket onto the box. The 40mm tube simply went into the socket but applied a silicon glue to close any gaps between.

Most important but used very practical solution was the dust filter. I bought a soup stock filter bag from Asian grocery store. I decided wrap this in four layers around air intake holes drilled on the large tube (40mm) using a paint masking tape (a replacement is also easy).

An external dimension of the 40mm large tube is not exact fit to the 2 inch EP holder (PVC pipes are indicated with an internal diameter but not external diameter). A purchased pressure PVC pipe was very close but still needed to tape up a couple layers of cloth tape until have exact fit to the EP holder.

Outcome you could see the next post in pictures. The first defocused image was Antares after left my 12 inch for 2 hours in outside without cooling fan on 19th Juy. The second image was Antares after running the cooling fan for 1 hour on 1st August. The third image was taken on the same day after running the cooling fan for 2 hours (Antares went behind a building. This is Kaus Australis. That’s why the colour is different). I can see clear improvement.

I’m happy with this new handy instrument. Only moderate concerns are: (a) whether any air holes hiding around focuser or the primary mirror covers (around a focuser knob or a mirror lock). I taped up unknown hole found next to the focuser knob just in case. If the scope is inhaling any airs without passing through the filter, this will accelerate dust accumulations, (b) the 80mm DC fan might be too powerful and pumping up air faster than an assimilation speed of the internal optical tube and mirrors.

The main unit should be kept in a dust proof case. For this reason I made a 12V cable detachable to the unit because often the cable picking up dirt and dust from the ground.

Hisanori
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Last edited by Hisanori; 09-08-2020 at 11:14 AM.
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  #2  
Old 08-08-2020, 05:29 PM
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Hisanori (Hisanori)
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Additional photos

Please see the additional photos.
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Last edited by Hisanori; 08-08-2020 at 06:59 PM.
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Old 08-08-2020, 06:50 PM
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Tulloch (Andrew)
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Nice, thanks for the instructions
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Old 08-08-2020, 07:04 PM
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Nice job but the wisdom these days is insulation not cooling.
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Old 08-08-2020, 08:05 PM
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That's awesome! and sure beats drilling holes and attaching peltiers to the actual back plate of the telescope.

Good one for all the planetary imagers on IIS to watch!

John K.
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Old 09-08-2020, 11:57 AM
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Sunfish (Ray)
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Great idea and good design to draw in external air through a filter which most designs overlook. Polyester fibre insulation would also make a good filter and I wonder if some medium such as silica beads could also dry the air.
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Old 03-09-2020, 09:03 PM
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Home Made SCT Cooler and Home Made Optical Tube Dehumidifier

Thanks for all your comment!

Inspired by Ray's comment, I prepared two bags of silica gel using the same soup stock bag used as the air filter. Then wrapped around the air filter using rubber bands. The opening of the silica gel bag was stapled closely. Once the silica gel absorbed moisture the whole bag can be dried in an oven (100 - 120 degrees) It works!

In addition, I made a dehumidifier to attach EP folder to keep inside OTA moisture free (while keep in storage). Jaycar sells a sealed ABS box with a clear rid (a changing colour of silica gel can be seen without opening the box).

All works very well at a fringe of cost. (Except I needed to invest a hole saw for the exact size of the PVC tube... thought around $25 ).
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Last edited by Hisanori; 07-09-2020 at 06:02 PM. Reason: New work was done
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Old 07-09-2020, 08:57 AM
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Quote:
Originally Posted by MortonH View Post
Nice job but the wisdom these days is insulation not cooling.
Perhaps.
But with an SCT Cooler on my 8" SCT, I got perfect star images at the start of the night after 45 minutes with the SCT Cooler in the scope during twilight.
When I didn't use the cooler, it was 3-4 hours before I stopped seeing thermal issues in the scope.
The reason was because I stored my scope at home in a closet that was usually around 20C, but my observing site was typically 10C at sunset and 0C about an hour and a half later and maybe -5 to -8C by dawn. The scope was always WAY too warm compared with the air.
The SCT cooler got the interior of the tube down to the ambient temperature quickly. In the middle of the night, I'd take a break and put it back in for 15-20 minutes while I was eating or using someone else's scope.
It worked like a charm and gave excellent star images when seeing allowed.
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Old 07-09-2020, 09:15 AM
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Sunfish (Ray)
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Well done. Great result that the air is clean and dry.
For $25 you can buy a pack of cheap hole saws of different kinds which are good enough for plastic. The more expensive bi metal type I use on aluminium and hardwood. Be careful , clamp it all down to timber and go slow, or use a pedestal drill.

Quote:
Originally Posted by Hisanori View Post
Thanks for all your comment!

Inspired by Ray's comment, I prepared two bags of silica gel using the same soup stock bag used as the air filter. Then wrapped around the air filter using rubber bands. The opening of the silica gel bag was stapled closely. Once the silica gel absorbed moisture the whole bag can be dried in an oven (100 - 120 degrees) It works!

In addition, I made a dehumidifier to attach EP folder to keep inside OTA moisture free (while keep in storage). Jaycar sells a sealed ABS box with a clear rid (a changing colour of silica gel can be seen without opening the box).

All works very well with a fringe of cost. (Except I needed to invest a hole saw for the exact size of the PVC tube... thought around $25 ).
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Old 07-09-2020, 10:24 AM
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If SCT's require battling with cooling issues because of closed tubes, I'm suprised they don't do truss SCT's in the same way they do RC's. Maybe there's something to do with the corrector plate picking up reflections from behind the scope?


Markus
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