Fitting a cooling fan

[bcfcciderhead]

Been thinking about fitting a small fan (pc type) to the rear of my 200p, electrics not a problem to me but a few questions, first of does anybody know how thick the primary mirror of the 200p is? i think anymore than 1.5" then a fan wont work?, and do they work?

keep hearing that some use a small hair dryer, but this will blow warm air i thought we need to cool the mirror to the "outside" temp?

Been looking into the fitting and of course it should not be fixed straight to the mirror/tube becaues of vibration so will look into using elastic to have it suspended by 4 bands in the centre of the mirror, it has a small recess between the rear of the mirror and the outside of the tube so hope it will fit here.

Got a few ideals but any more info will be great

[dweller25]

I fitted a small fan to a baffle to make sure all the air blew up the tube - it worked a treat on the 200P, well worth the £4 :-))

[bcfcciderhead]

Thanks David, thats looks a proper job, i take it you have the 200p then? so a question for you, next to the primary mirror adjustment screws there is a small hole (3 in total) threaded i think, what are these for? they look like "spare" screw holes to me maybe for adding a fan, and by looking at your pic it looks like you have used them to fit yours, also what is the baffle made from? i guess this stops vibration

[dweller25]

The three small threaded holes are for the 200mm F/5 version which does have a rear plate and uses these for attachment.

The 200 F/6 version has no plate so I made one from an aluminium clock face. I attached the fan to this plate and then attached the plate to the OTA using the three spare holes.

It worked really well.

I have since sold the 8" and moved up to a 10" but have again added the same fan/plate system.

HTH

[bcfcciderhead]

Thanks for that David i think thats the route i will go down, but my biggest fear is going to be vibration, do i leave the fan on all the time while viewing or just for say about 30mins before?

[dweller25]

I leave the fan on and even at x343 I see no vibration.

It's really cool to turn the fan on and off during observation - those bad nights you get where the seeing comes and goes suddenly disappear with the fan turned on.

The advantage of adding the fan to the plate is that it makes no changes to your OTA and you can fiddle and optimize to your hearts content.

Let me know how you get on.

Clear skies.

[sixela]

Been thinking about fitting a small fan (pc type) to the rear of my 200p, electrics not a problem to me but a few questions, first of does anybody know how thick the primary mirror of the 200p is? i think anymore than 1.5" then a fan wont work?,

On the contrary. It will take longer for the mirror to cool, but that means a fan is even more necessary.

keep hearing that some use a small hair dryer,

Those are used to keep dew at bay. Different issue.

[bcfcciderhead]

Thanks for pointing that out about the thickness of the mirror..makes sense now

and so does the hair dryer thing...DOH!, never had dew on the primary as yet but the secoundary is a different matter

[sublime_mick]

if you look through the fan can you see any part of the back of the mirror and will this have an impact on viewing? (or id there a blacked area bewtween fan and mirror?)

[dweller25]

if you look through the fan can you see any part of the back of the mirror and will this have an impact on viewing? (or id there a blacked area bewtween fan and mirror?)

Yes you can see the mirror but it has zero impact on viewing.

[sublime_mick]

thanks dweller25 - i made a baffle and attached the fan - everything was looking fine and i realised the mirror was quite exposed.... that's what got me thinking - as i have the blue tube explorer 200 (which came with a back plate which completely covered back end). i believe the newer models have the back end completely exposed - so this allays my fears. - thanks again