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DIY Cooling fan

kev1204

By kev1204
in DIY Astronomer

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kev1204

kev1204

Posted
Posted

Hi,

Have rigged together a cooling fan for my 12" skywatcher flexi tube.

There are tapped mounting holes on the mirror bracket so I thought I'd fix a fan to it.

80mm fan with a fan speed controller.

For easy power connection I have used a 2.1mm socket mounted in a small hobby box to connect to a 12v portable power supply, the kind of thing that gives your car battery a boost on the cold mornings, using a fused cigarrete lighter connector. Fitted a red LED across the live and earth with a 820 Ohm resistor

Im going to mount the control box on the side of the scope mount and fit the fan and guard in the morning.

The whole lot cost no more than 15 quid!

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Very Pleased!!!

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kev1204

kev1204

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Fan fitted to scope. Not too sure about the fan guard. It protrudes out too far. Not sure of its worth, I'm not likely to stick my fingers in it when its running.

I'm going to fit some decent connectors though - maybe DIN plugs between the fan and controller for easier disconnection , and I'll probably sleeve the cables too, But not bad for under 15 quid.

If the LED is too bright then I'll just up the resistance to dim it down.

I might not get so fed up if the scope cools down quicker, rather than dragging it outside to cool for an hour then the clouds roll in as its ready.

I dont know why it doesnt come with a fan, after all the mounting holes were allready in place.

Cheers

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haitch

haitch

Posted
Posted

Nice job. I'll have to sort something out similar myself at some point.

Can I just ask if anyone knows if it is better to blow at the back of the mirror or draw air off?

I wondered if directing a stream of air at he centre of the mirror might cause it to cool quicker than the outer edges which probably wouldn't be helpful.

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Astronut

Astronut

Posted
Posted

Nice job. I'll have to sort something out similar myself at some point.

Can I just ask if anyone knows if it is better to blow at the back of the mirror or draw air off?

I wondered if directing a stream of air at he centre of the mirror might cause it to cool quicker than the outer edges which probably wouldn't be helpful.

I remember reading somewhere it's better to blow air to the back of the mirror - makes sense when you think about it.

I'm thinking of doing something similar to this. I have a few spare low profile 12V case fans lying around and one of these will do nicely. I've checked and the fan lines up perfectly with the screw holes at the back of the cell. Nice of Skywatcher to add ready made mounting holes to the cell :)

It's the thermal layer just above the mirror surface that's hardest to get rid of - I remember reading a DIY thread somewhere with pictures showing a baffle system to direct the air flow so I'm thinking of adding a baffle plate to the back of the cell so that air is directed around the back of the mirror and up the sides of the cell into the tube and over the mirror surface to break up the thermal layer. I think the thread was in the iceinspace (Australian) forum. I'll try and find it.

My mistake - it was on cloudynights here

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kev1204

kev1204

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Thanks for the comments!

I took the fan guard off. It stuck out from under the scope base by 10mm or so.

Just need a 2 speed crayford and a telrad when funds allow. Dont think im going to bother flocking the tube. Gonna get the missus to sow me a cover to fix around the open part of the tube and that will be that.

Great site BTW

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Astro_Baby

Astro_Baby

Posted
Posted

Ian,

I read an article some time back about removing the surface layer. Yes you need a baffle is the answer.

I have a similar project on for my 8" when I get time to carry on filing bits of metal off :)

Theres also a school of thought that suggests having a very tiny fan held just above the primary by thin wires ( like a mini spider vane ) that blows air onto the face of the primary. I Like the idea of that but mounting it would be a nightmare as it would be in the way when you want to collimate.

Heres the article http://www.fpi-protostar.com/bgreer/fanselect.htm

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kev1204

kev1204

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Hi Astroscot2,

The fan cable disconnects from the speed control box mounted on the base. I didnt want it permanantly connected as I seperate the OTA from the base when I move it outside. Its only a small connector buy I will upgrade it to something more substantial.

Tried it in anger tonight - in 20 mins the scope was cool enough to see well.

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Astronut

Astronut

Posted
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Ian,

I read an article some time back about removing the surface layer. Yes you need a baffle is the answer.

I have a similar project on for my 8" when I get time to carry on filing bits of metal off :undecided:

Theres also a school of thought that suggests having a very tiny fan held just above the primary by thin wires ( like a mini spider vane ) that blows air onto the face of the primary. I Like the idea of that but mounting it would be a nightmare as it would be in the way when you want to collimate.

Heres the article http://www.fpi-protostar.com/bgreer/fanselect.htm

I was reading that page last weekend. Seems like too much trouble for a normal sized mirror. If I had a 30" Obsession (dream on :) ) it probably would be a worthwhile mod but for an 8 or 12" mirror I think a baffling system would be more than adequate :)

I'm going to try just adding a removable back baffle around the fan covering the tube end first to get maximum airflow from the fan - removable so I can revert to normal passive cooling once the mirror's reasonably stable.

If that doesn't break up the mirror surface thermals then a simple ring of material (inside diameter slightly wider than the mirror) mounted to the inside of the tube slightly above the mirror surface might act as a second baffle to direct the airflow over the mirror. Similar to the project linked above but I haven't decided on what materials to use.

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  • 1 year later...
Moonshane

Moonshane

Posted
Posted

hi all

I have a slightly different but related quandary. I am buying a 12" dob which already has a side fan which blows air across the mirror which seems a great idea and I may keep this. see pics. there are also 'vent holes opposite the fan. with the purchase comes a spare tube - amazing I know! - which is 'complete'.

my dilemma is that the scope has to come apart to check the coatings and fit the 4 vane spider so which tube should I use??

I am veering toward the fan version and keeping the other tube as a complete spare. the collar slides to close the vent holes when not in use or if air flow seems better via the up and out route.

any comments very welcome!

cheers

Shane

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