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Active cooling needed for C11 stored outside?

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#1 adamsdp

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Posted 17 March 2019 - 10:37 AM

I live in Michigan and store my CPC 1100 outdoors in a shed and wondering if active cooling would be helpful?  The scope should be near ambient temperature at the start of observing.  Will a C11 typically be able to keep up with falling temperature enough so it doesn't impact image quality in the climate I live in?  My understanding is that the lymax cooling fan will help with initial temperature equilibrium while a system of vented fans moving air in and out of the ota while observing will help with the scope keeping up with falling temperatures as well as initial cooling.  I don't think I am up for cutting up the ota and installing fans so wondering if the lymax cooling fan could be worthwhile or if there are other solutions?  Thanks!



#2 junomike

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Posted 17 March 2019 - 10:47 AM

In the Spring and Fall my SCT's have troubles with the drastic temperature change/drops that can and do occur.

That being said I really only notice it when viewing Planets and Luna.

I had TEMP-est fans in an 8" EdgeHD which worked wonderfully but there were a few outings were even they had trouble keeping

up with the temperature delta.



#3 Chris Johnson

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Posted 17 March 2019 - 12:14 PM

The temperature inside my shed in the spring and summer is 20 to25 deg f warmer than ambient temperature. I have concerns about the grease used to lubricate the baffle tube, tuning at those temperatures. My scopes are stored in an unheated garage under my house. 



#4 Cajundaddy

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Posted 17 March 2019 - 12:52 PM

With an SCT I prefer to slow the cooling of the OTA with a Reflectix wrap and dew shield.  This reduces or eliminates internal tube currents and has the added benefit of reducing dew formation.  As long as the scope is above dew point, your optics will tend to stay dry.  A better solution than active cooling fans IMO.

 

https://www.amazon.c...441690764&psc=1


Edited by Cajundaddy, 17 March 2019 - 12:53 PM.

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#5 skybsd

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Posted 17 March 2019 - 01:00 PM

Hello Dave, 

 

I live in Michigan and store my CPC 1100 outdoors in a shed and wondering if active cooling would be helpful?  The scope should be near ambient temperature at the start of observing.  Will a C11 typically be able to keep up with falling temperature enough so it doesn't impact image quality in the climate I live in?  My understanding is that the lymax cooling fan will help with initial temperature equilibrium while a system of vented fans moving air in and out of the ota while observing will help with the scope keeping up with falling temperatures as well as initial cooling.  I don't think I am up for cutting up the ota and installing fans so wondering if the lymax cooling fan could be worthwhile or if there are other solutions?  Thanks!

 

Helpful is relative., 

 

You didn't mention state whether your shed is heated or not, but the fact that your OTA is stored outdoors is already better preparation that if it were to be stored indoors in your (presumably heated?) home. 

 

That said - how well your OTA track ambient is largely driven by: -

  • How fast your local temperature falls are on average 
  • How long the (fast) temperature drops continue during your session 
  • The size of your OTA 

Because the first two will change over the course of an season, its best to simply see what your experiences with your current storage arrangements before considering any modifications to your OTA. My own experiences with the SCTs I own is that over the course of a night, there certainly are periods where the temperature keeps falling (fast) all night for (what seems like) all night. On the other hand, there will be other periods when you start noticing that more and more, at some point, the rate of temperature change plateaus, and for 2 - 3 hours, your scope will really start showing what its made of.., 

 

These are the moments us visual only observers dream of! lol.gif  

 

Hope this helps.., 

 

Best.,

 

skybsd



#6 mich_al

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Posted 17 March 2019 - 08:00 PM

In the Summer you'll need active cooling to keep it tracking with temps as the night goes on and likely to get it to temp when starting.  Lots of thermal mass in that 11". Search on how to identify a thermal plume so that you know it when you see it.  A problem with Lymax is that you can't observe when it's installed.



#7 Bean614

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Posted 17 March 2019 - 08:01 PM

I second Cajundaddy's insulation suggestion.  My C11 is outside, on my deck, 365 days per year.  It is wrapped in insulation, and when not in use, is under a Telegizmos 365 cover.  Temps DO drop fast here in New England in Fall, Winter, and Spring, and the insulation slows the cooling to a minimum, eliminating currents.  It's good to go the minute I remove the cover.



#8 adamsdp

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Posted 17 March 2019 - 08:35 PM

Thanks for all the replies and information!  I never heard of wrapping the ota in insulation and sounds like a great idea.  I will buy some and try it out.  Do you wrap the ota only or the ota and dew shield in the insulation?

 

Good point about seeing how the scope performs over the different seasons.  The shed the scope is stored in is unheated so hopefully this will help the situation.  



#9 macdonjh

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Posted 18 March 2019 - 10:55 AM

I installed fans in the C11 I used to use. They helped my scope cool off when I was at star parties and my scope was outside, under a standard Telegizmos cover all day. It still got hot, aluminizing or no aluminizing.

That said, there is a growing number of SCT users who find insulating their scopes to be better than cooling them. Reflectrix is inexpensive and reversible, too. Perhaps worth a try.

#10 jhayes_tucson

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Posted 18 March 2019 - 11:25 AM

Here’s what I’d do:  I’d put a small window cooler on the shed and I’d set it for the expected temperature when the sky is completely dark (end of astronomical twighlight.)  If you don’t want to run it all the time, you could put it on a timer to start at least 3 hours before dark 

 

John


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#11 adamsdp

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Posted 24 March 2019 - 11:55 AM

I bought some insulation and wrapped the ota of my C11 as shown in the picture below.  For those who have had success with in reducing tube currents with insulation, have you wrapped back end of the ota where I haven't?  I also made a dew shield out of the insulation that slides on the front.  Thanks.
 
C11 insulation

 



#12 KerryR

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Posted 24 March 2019 - 04:19 PM

I added active venting to both my 8" LX90 and my CPC11. It made all the difference in the world.

 

I tried a Lymax for both. The Lymax helped with initial cooldown, but, obviously, the advantage is lost shortly after the fan is removed. I also tried adding insulation to the ota. The insulation thing worked well, but I got better thermal outcomes with the fans.

I think the ideal solution is probably tube insulation and active venting. Eventually, I'll get around to adding insulation, at least to the 11".

 


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#13 adamsdp

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Posted 25 March 2019 - 08:45 PM

Took the scope out tonight and I think the insulation is working quite well.  Wasn't out long but trapezium low in the sky look pretty steady, much improved over the last few times I had the scope out before putting on the insulation.  Polaris and companion both looked relatively stable.  Thanks for the great idea!



#14 KerryR

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Posted 26 March 2019 - 12:30 PM

At some point, you should consider adding insulation over the rear casting as well- that's a source of thermal discontinuity as well.




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