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Cooling fans on a Skywatcher 200P


Wbarkingmad
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Has anybody tried mounting cooling fans onto the back of a skywatcher 200P or similar OTA? The evidence seems to be in favour of fans being a good thing but do I need to modify the back end of the tube to fit them or is it sufficient just to blow air onto the existing end cap assembly? I'm thinking along the lines of 3 CPU fans or similar.

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I put one on my 12" dob and built this into the end cap (see http://stargazerslounge.com/diy-astronomer/109577-latest-dob-mods-fan-balancing-weight.html). I also have a side mounted fan to blow air across the primary. They certainly help with cooling (I keep both end caps on and blow air out of the focuser) and I believe also the views at high power (I leave the fans on when observing but as slow as possible).

I am contemplating adding a single small fan to my 6" dob too.

I don't think you'd need more than a single fan on your 8".

see also:

http://stargazerslounge.com/equipment-discussion/104657-cooling-fans-do-more-than-just-cool.html

there are lots of ways to do this and much online about adding fans to newts generally.

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i mounted a fan on the back of my 250px by attaching it to a neoprene circle which is velcro'd in place. The thinking was the neoprene would help lessen any vibrations. Mines a 80mm pc case fan attached to a 4 AA battery pack.

I totally agee about the steadying effect of fan while observing.

Brian

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So, when you do this, are you also trying to seal the fan/baffle arrangement at the primary end so that any pressure created by the fan is pushed up and out of the holey end (technical term) or is that not a factor? ie replacing as much air 'inside' the tube as is reasonably possible, also, does this have any effect on reducing dew?

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Yes, in fact the fan will do three things :-

Accelerate the cooling of the primary to ambient.

Remove the thermal boundary layer from the front of the main mirror.

Remove the thermal gradient between the inside of the OTA and the outside.

HTH

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Yes, in fact the fan will do three things :-

Accelerate the cooling of the primary to ambient.

Remove the thermal boundary layer from the front of the main mirror.

Remove the thermal gradient between the inside of the OTA and the outside.

HTH

Uh-oh, looks like I have landed myself another mod job...;)

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I use my fans with both end caps on and so that the air is blown out of the focuser.

One good thing about this is that you can feel with your cheek how cool the air is and when you are ready to observe (roughly.)

Edited by Moonshane
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