Heath Robinson Cooling Solutions !

[Blackheart]

Hi all

Just thought I would share my little cooling fan project. Having been convincd that thermal issues were affecting the quality of the view trough my 12" flextube I decided to have a go at addressing the issue. I looked at several other people's answer to the cooling fan problem and admired their craftsmanship and electronic prowess. Variable speed fans, perfectly fitted backplates and leads...

However, being perennially short on cash I decided to have a go at attaching cooling fan on the cheap. I took out the small cooling fan from an old PC we had in the garage and thought this would do to blow cool air on the back of the mirror while not imparting too much in the way of vibrations.

I used the lid from an old Ikea storage box and basically cut it into a circle and used a sturdy modelling knife to expand the hole in the middle. This would provide a baffle around the fan to prevent the air from just slipping round the fan without circulating across the face of the mirror.

I used sticky pads to attach the fan and silver duck tape just to finish off and seal the edges (very sophisticated!) I got a cheap 8xAA battery holder off ebay (£2) and I have filled this with rechargeable batteries. The fan now spins away merrily. Attaching the fan required the highly technical use of Blu-Tak. Three good dollops on the back of the mirror cell and the fan and baffle are securely attached but can be taken off with a simple peel.

To aid with initial cooling I decided to make an extractor fan to draw air past the mirror and out of the tube. With this in mind I got a larger 120mm fan off Ebay (£2). I then cut out some card to match the size of the tube caps. I cut a hole in the middle and attached the fan with the tried and tested method of sticky pads! Some good old silver duck tape gives it veneer of weatherproofing and makes it look more high-tec (I'm sure you'll agree). I intend to use a simple AC/DC 12volt adaptor to power this larger fan, although I could just use another battery pack.

So now, when I put my scope out to cool I have a fan drawing warm air out of the tube and a smaller fan blowing cool air onto the back of the primary mirror. When I come to observe I remove the extractor fan but I leave the smaller fan in place. There is no sign of vibration so hopefully it will help to keep the mirror at ambient temp.

First light results showed a slight but deffinite improvement in the views of Jupiter. I might try placing a small fan inside the tube to blow air across the surface of the mirror but I am going to make sure my collimation is accurate before pointing the finger of blame anywhere else.

Anyway, just thought some of you might be interested to see how you can contrive a cooling fan solution for less than a tenner (I already had a bunch of rechargeable batteries lying around). Take a look at the photies and see if you find anything useful...

Clear skies

BH

[Mike Hawtin]

Great stuff, a man after my own heart, I love knocking things up from what I have around, some of it even works! I seem to recall reading somewhere though that having the fan blowing across the face of the mirror was the most effective cooling solution but I'm blowed (pun intended) if I can recall where I saw that.

[Blackheart]

Yes Mike, I think you are right. Apparently blowing across the surface clears the thermal boundary layer that sits over the primary mirror. I think I will do it although I might need a new pack of sticky pads!