SCT Cooler part III

[davidpretorius]

Ok, unpacking a D1ck smith 12 volt fridge and getting the cooling system out

http://www.precons.com/iceinspace/articles/peltiers.aspx

[matt]

Good stuff Dave.

Nice and detailed with plenty of pics to demonstrate the process bit by bit.

That's excellent for those of us who need a bit of help:thumbsup:

[Lester]

Great post Dave, I love pulling things apart (constructively ofcourse)

[asimov]

Nice one Davo. So it is thermostatically controlled. Has to be obviously, have to have some control over the temp, other wize you'd end up with frozen beer!

[Lester]

Hi Dave,

Just pulled a **** Smith fridge apart looks very similar to what you have done. I am thinking of mounting the peltier flush onto the outside of the OTA, at the top because that is where the warmest air will be internally. I thought that the cold from the aluminum peltier block would transfer very quickly through the metal tube on the SCT. I was thinking of putting it on the casting at the rear behind the primary, but temperature transfer would be much slower because of the thickness of the casting.

What are your thoughts David?

[davidpretorius]

Two thoughts

1. Paul haese is looking to do this exact same thing with a c9.25 in adelaide
2. Whilst something is slower to transfer the cold from the cold plate, it is slower to lose it as well. If 1 x peltier system has enough oomph to cool the back plate or in essence the whole tube assembly them that will mean the air inside will cool better.

If i start my peltier up and measure the temp it drops to, then it is -2 or less. Whack a cold plate ie a 180mm x 2mm alu disc, then it will drop to say 10 degrees below current ambient temp. As soon as i start up the circulating fans, this ends up being a 5 degree difference as i am effectively cooling the air, but warming the cold plate by circulating the air.

You have 4 bolt holes on the cold plate, which you can attach the cold plate to the back of the tube and also a smear of thermal paste (from dork smith or jaycar, just so you transfer as much cold to the back of the tube.

Circulating the air will still be essential in side the tube ie via cat cooler or some small fans located behind the mirror.

I am very intersted in the results. I have asked Celestron about this, but am yet to get a reply?

[Lester]

Thanks for your reply David,

Because the peltier block is 2cm thick and that is where the thermostat is placed I will place it inside styrophome to stop the cold from escaping out the sides.

If you don't mind I will inform you on this thread. Or would you rather I start a new one?

[davidpretorius]

i cut the thermostat out as i have sensors on my reflector mirror to update me.

please keep posting to this thread as it makes it easier for others to find.

thanks for testing the ideas, this is fun!

[davidpretorius]

interesting reply from celestron but i spose not unexpected

"

Cooling the SCT's via peltiers

Hi Dave,

We offer no recommendations on modifications of our telescopes - can tell you however that we do not have plans to add cooling fans to the back of our Schmidt cassegrains as we are averse to the possiblity of adding an foreign materials inside the optical tube which a fan certain would do.

Thanks,

Celestron Tech Support

Celestron.com
(310) 803-5955"

[asimov]

Wot rubbish....oh ok Celestron, we shall continue to wait 3 or 4 hrs for the thing to cool so we get decent tube current free views & photographs.:lol:

Get your patents in quickly I say.;)

[Lester]

Looks like we have got Ground Breaking technology going on here chaps. Highly sofficticated too.

[Lester]

Okay chaps, been doing a lot of thinking about the Cat Cooler as I dismantled the fridge.

I was going to mount the peltier with octopus straps in a foam surround on top of the tube. The foam would be to stop cold air escaping horizontally, and the peltier would be touching the tube directly.

Then I got thinking, the peltier is only 3" x 3" trying to cool a much larger area. I am always looking for the easy way out.

What would be wrong with attaching ice packs with octopus straps, and monitoring the temperature of the telescope with a thermometer and the ambient air temperature also. Then by estimating how much the air temperature is going to drop from sun down to observing time, you could apply 1 or more ice packs. Okay it will be trial and error at first, but once you know how many degrees the night will be colder than the day temperature, you apply 1 or more ice packs and for a set time.

Sounds so simple to me. Your comments will be gratefully received.

[matt]

Lester...

In the words of the Immortals... "try it and see, mate!"

[asimov]

Bought myself the same Richard Smith 12V fridge today, along with the temp. sensors......Let the great SCT cooling experiments commence!! :D

[Lester]

Hi everyone,

Here is an update on where I am at with the sct cooler.

The Peltier strapped to the top rear of 14" SCT tube and insulated so that the cold temp had to go through the tube and didn't escape into the air, didn't do much. :P

I have just strapped 3 ice packs to the rear of the tube and will monitor the temp= ambient and internal tube.

Will give update this evening on the results.:D :whistle:

[Lester]

Hi,

Cloud and thick unfortunately. :doh: Just removed the 3 ice packs that were strapped around the primary mirror end of the tube for 4 3/4 hours.
at the beginning ambient temp=16.4 and internal tube=18.1
4 3/4 hours later ambient temp=12.4 and internal tube=11.5

The minimum temp in the last 24 hours was 8.4 and max=23.9 this is inside the observatory.

Unfortunately I couldn't check what the seeing through the telescop was like, because of the thick cloud.

Does a telescope that is 1 degree above ambient have the same seeing caracteristics as a telescope that is 1 degree below ambient?

The research will continue.

[davidpretorius]

sounds good lester,

i am in frustration mode. as we speak I have just bought inside my telescope as I can't even see the moon, let alone the occulting of antares....grrrrrrrrrrrrr

i had a look at the temps and the mirror was 6.1, ambient 6.3.

What a waste!!!!!

[matt]

Yo Davo...

Happy 5000....:cool:

[davidpretorius]

thanks matt!