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Can I have some members cooling fan solutions please ?

spaceboy

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LukeSkywatcher

LukeSkywatcher

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Sit it outside lol :)

That would be my suggestion, but i read somewhere on here many moons ago that a cooling fan is pretty essential if you are imaging as it keeps the mirrors at a constant temp all night whereas if imaging without a fan..................you mirror is open to subtle temp changes through out the night and this can mess up your images.

Correct me if i am wrong...............but i think that was the gist of what i read about needing a cooling fan.

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Moonshane

Moonshane

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very neat job Nick.

I completed mine too at the weekend. not as neat but the end cap (made from two layers of garden weed matting) acts as a filter. I'm not a fan of wires either but as they go to the battery in the base it's not going to tangle on anything.

John has kindly offered to supply a cover to save any scary moments when collimating - no pain, just makes you blummin' jump when your fingers touch the whirring fan!

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LukeSkywatcher

LukeSkywatcher

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OK thanks. That photo really puts the size of a 16" light bucket into perspective. I guess it is not much of a storage/moving issue if you have it on castors.

Haha, dont get me wrong. I am not sizing one up as my next upgrade. Although your image gives me a glimmer of hope for the future.

LOL..............ANY OF MY 3 SCOPES WOULD BE A FINDERSCOPE ON THAT THING.

What height are you?

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Moonshane

Moonshane

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to be honest, if I could store it outside, I probably would and then castors would be good and easy. as it is I put it on a sack truck and roll it out in two parts.

see my thread for more details as I don't want to be a hijacker!

http://stargazerslounge.com/diy-astronomer/140533-16-f4-orion-optics-uk-dobsonian-project.html

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spaceboy

spaceboy

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were did you get that massive fan from?

Don't ask. I gave it a try out when it arrived the other day and felt it would be more suited as a desk fan to keep me cool in the summer than strapped to the back of the scope. 57cfpm at full tilt so the plan is to use the dob as a cloud cannon and blow all the clouds away prior to observing :)

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jimmyjamjoejoe

jimmyjamjoejoe

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So, all you guys with fans, do you suck or blow? :) According to the previously linked article, it produces far more stable results far quicker to have the fan blowing out the the bottom of the tube.

This is due to the fact that the biggest problem is the "false lense" of heated air just above the primary, rather than the tube currents which are sorted fairly quickly and easily.

Blowing into the tube is a kind of brute force "cool everything down", but is very turbulent in doing so, and takes a long time. Blowing out the bottom of the tube however produces a steady suction, pulling air steadily across the primary and down the sides, removing the false lens without turbulence, and without pushing that heat further into the tube, instead it is ejected turbulently outside the tube where it doesn't matter.

Dust was my initial concern with this method, but apparently it isn't a noticeable problem.

Any opinions?

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Moonshane

Moonshane

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to be honest I don't know enough about the science of this but am dubious about any major effects either way and don't think it matters which way the fans blow. I mainly use mine for cooling and it blows up the tube. It would be easy to insert a switch to drive the fan one way or the other with the same wiring and I may try this.

unless in a dusty environment, I don't think that it's an issue outside anyhow.

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spaceboy

spaceboy

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If it has no noticeable improvement blowing I will turn the fan around and suck :) Although saying this would sucking air into the OTA also be sucking whats falling objective end IE: dew ??? A cooling mirror and damp air being drawn into the OTA may be a recipe for problems ??

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LukeSkywatcher

LukeSkywatcher

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Hang on I just thought. Hot air rises. Sucking is pulling against the natural flow. Surely blowing is going to have a more efficient way of removing the warm air ??? and in turn speed up cooled down times and get observing quicker ?

Thats a very good point.

Maybe scopes need extractor fans fitted?

Less sucking...............more blowing.

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spaceboy

spaceboy

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I have been pondering on the thought of if I made a mistake in ordering such a large fan. Although the fan turned out to be physically bigger than expected I have tried to be optimistic and figure out some benefits in having an over sized fan. I have come up with 1) As the fan is almost 1/2 the size of the primary this should cool the mirror more evenly and reduce any small flex / distortion in the glass as it cools ?? 2) larger the fan the slower it needs to be run to accomplish the same cfm as a smaller fan would at full speed and the less vibration it will cause in doing so. Telescope Optics Topics would suggest a 10" Pyrex mirror requires a fan either side of the primary producing 15 - 25 cfm of air flow to cool the primary efficiently. At a rough estimate the 120mm fan will produce 30 cfm @ 5v cooling the primary and what ever excess removing thermals from the OTA (fingers crossed) 3) As the rear of the scope is now baffled it should help to reduce stray light entering the base of the OTA. If I choose not to run the fan any longer I can leave the baffle in place while still having a large fan hole allowing ever cooling ambient air into the primary. 4) As I run more than one accessories at a time off my power tank the hope is running the fan at 5v will also be less of a strain and drain.

I'm putting my faith in the fact that this has been a long debated argument for the actual benefits of using fans in telescopes. I have certainly found many a colorful graph showing the benefits on paper and I sure can tell when a scope is being effected by thermals in the OTA as apposed to seeing conditions but only time will tell if my money was well spent.

Thanks to everyone who posted suggestions and pictures of their cooling fan solutions. My scope is now for hire if you have a bouncy castle in need of pumping up :)

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Moonshane

Moonshane

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Thanks to everyone who posted suggestions and pictures of their cooling fan solutions. My scope is now for hire if you have a bouncy castle in need of pumping up :)

:evil6::D

like many things, it's unlikely to have much difference in effect either way so don't sweat it. just use the fan and use your scope :)

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johninderby

johninderby

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I've experimented with cooling fans and have found that actually you don't need or want a big powerful fan. In fact a 60mm fan cools down my 14" dob very nicely.

The biggest mistake that I see made is to blast air at high speed over the back of the mirror. That's very ineffective as the air is simply moving too fast. The airstream has to be moving slowly enough to allow enough time for the transfer of heat from the mirror to the air. It's easy to be mislead by thinking of cooling yourself down with a fan where a powerful fan does indeed cool you down faster, but that's cooling by evaporation which is a different matter entirely to cooling your mirror.

If you want to cool down the inside of your Newt OTA quickly make up a disc to cover the front of the tube with a few fans mounted in it and blowing outwards to suck the warm air out. A few minutes of this should cool down the interior quite a bit and then you can remove it. Would be a good idea to temporarily cover the other end of the tube with some sort of filter material to stop dust being sucked in.

John

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