My take on peltier cooled newt mirror.....

[Kokatha man]

Not sure if some of you Northerners have quite the need for mirror cooling as we do down under but it may be usefull for some who do planetary imaging with Newts (or adapted to other designs.)

Anyone struggling to bring the mirror temp down (or possibly even up) to ambient air temp will appreciate that untill the mirror reaches thermal equilibrium image distortion and image quality is a major factor in final imaging quality for planetary imaging with reflectors.....I have added my own modifications to designs that are successfully used down here in Oz to add a little more sophisitication and efficiency to some of the units people have constructed.....:D

As I comment in the article, this unit has only been bench-tested as I am still working on the electric slomo alt/az controls of my Dob-based 12" Newt.....it sits on a Round Table EQ platform and has electric focussing but the az slomo isn't quite finished.....hope to have it up and running for imaging Jupiter by opposition....!

In this unit I designed, I modified some of the concepts/construction details from other designs: numerous folk have utilized peltier cooling devices to bring their scope mirrors down to ambient air temperature, thus stabilizing any mirror surface distortion and subsequent image clarity brought about by the mirror glass contracting or expanding as it attempts to equalize with ambient air temperature.....it has only been test-run by itself without testing its' cooling effect upon the mirror in situ, but I have every reason to be confident of its' performance.....

Comments from others about needing to drive the air onto the coldplate via the internal fan to maximise heat transfer from the selfsame air circulating over the mirror caused me to develop this video card type unit…..

I substituted one of the regular types of internal fans commonly used with one from a video card chipset heat extractor.....a radial type fan with its' own finned heatsink which I affixed to my main coldplate (the sheet aluminium disk in the pictures) using heat transfer paste.....which means that these radial fins and their solid base under the fan are cooling extensions of the coldplate, receiving the full flow of air that this radial-type fan circulates across said radial fins which are in direct thermal contact with the coldplate and thus cold side of the peltier unit.

Also, these little fans are much more "gutsier" than normal chip cooler fans.....and re the preceding paragraph I believe this should markedly increase heat transfer/cooling; as well as give better, unhindered cold air circulation onto, and around, the mirror.....

This is because this type of fan has the added bonus of not retarding or having airflow “blocked” in any way, so that circulation at the back will invariably be much greater.....resulting in cold air reaching the mirror much more quickly and effectively.....

When bench-testing I noticed the (reasonably) large amount of condensation forming on the coldplate.....though this may have been exaggerated by the fact it was operating in the open air.

From other’s observations I didn't like the idea of any condensation having to find its' own way out, and my two little gutters/troughs idea evolved.....they are set at about 60 degrees from the coldplate and in situ the apex of the "V" is at the lowest point.....held on by tabs as in the photo and sealed with a smear of silicone all along, with a little "boxed" section at the "V" to allow condensate to "pool" there and thus assist its' discharge via the piping (5mm dripper tube and elbow.)

I kept the original control boxes whilst maintaining a modicum of order/neatness in the wiring runs…..I can run one or both peltiers this way, switch things on and off, and the green LED's let me know what's running.

After it has been bench running for 10-15 mins those radial fins get really cold.....as does the large amount of air these fans move; they really are gutsy little blighters....!

The pictures show the peltier plate setup (internal and external) for my GSO 12” modified Dob with the peripheral holes for the Bob’s Knobs collimating screws, also using the mirror lock screws to secure the plate to the rear of the scope tube as others have done.

[Kokatha man]

.....exposing some of my ignorance (but not. I believe, the efficacy of this untested in situ version) I should correct some of the abovementioned and acknowledge that it is the thin layer of air above the mirror as it attempts to find equilibrium with the air temp that is the major cause of image-quality degradation.....akin to "poor seeing."

I'm unsure of how being in colder climes than here this problem manifests itself.....in Oz (and similar climates) it is the fact that the mirror temperature finds itself nigh impossible to drop to air temp, thus having a boundary layer of warmer air above its surface.....that major distorting factor.....

[sublime_mick]

nice

[jimmyjamjoejoe]

.....exposing some of my ignorance (but not. I believe, the efficacy of this untested in situ version) I should correct some of the abovementioned and acknowledge that it is the thin layer of air above the mirror as it attempts to find equilibrium with the air temp that is the major cause of image-quality degradation.....akin to "poor seeing."

I'm unsure of how being in colder climes than here this problem manifests itself.....in Oz (and similar climates) it is the fact that the mirror temperature finds itself nigh impossible to drop to air temp, thus having a boundary layer of warmer air above its surface.....that major distorting factor.....

I read an article a while back that experimented with brute force cooling the mirror by blowing air on it from the sides, blowing in from the bottom and up the tube, or sucking down the tube, around the mirror and blowing out the bottom. The last one gave the best views straight away, due to the removal of the boundary layer in a controlled manner. It basically sucks all around the edges of the mirror creating a much smoother current of air which only becomes turbulent after it is exhausted from the tube, as opposed to once it has been blown a few inches up the tube.

Just found the article HERE