Guest Darrian Posted March 13, 2012 Share Posted March 13, 2012 Well seeing that i had four days i thought i'd better put it to good use, So instead of decorating or mowing the lawn , i instead sat down and watched one of Dion's astronomy shed videos. I sat and watched the one about the homemade cooling fan and was enthrawled at how easy it could be and that even a numpty like me could do it , so afterwards i sat down and did a bit of research and figured that it can be done for around £20. What i didn't count on was the fact that i couldn't find anywhere that sold Black perspex anywhere. Unless i wanted to pay the earth for a sheet of it that would cover an olympic sized pool. So Perspex aside i popped over to Maplins and picked up an (Antik 120MM Quiet Fan) Cost £10:99. (1 x 21.5mm DC input. Cost £1.49 (1 x 12v DC Red Rocker switch. £1.79 ( 1 x 120mm Metal Fan guard + Harware £4.99 1 x A4 sheet of velcro .99p What i still couldn't source was the perspex . And then it hit me like a blinding flash, I had loads of Perspex...... Off i went to the fathering laws and there it was stood in front of me , a 20ft long Caravan !!! A Caravan you may ask !!! I walked up to it and with my super human like strength i yanked one of the windows out !! The windows of course are made of Perspex and are ideal, The only problem is that it wasn't Black so that it matched the scope , But not to fear!! I still had a roll of my friend (Wilko's Black velour) So armed with my tools i locked my self away. and sawed and drilled and glued, and swore ..... The end result was somthing that i would be proud of and if i must say so looks quiet proffessional... I stuck it on the scope last night, and switched it on , the motor was as quiet as a mouse , No vibration , No shake,. Only a gentle breeze from the bottom to the top of the scope. As for images through either an EP or a computer monitor ( WOW what a difference) No Scooby Doo effect or at least very little. and it's clearly evident when you turn the fan off or reduce the speed to idle All together it was a fun couple of days , The total cost, Just over £19, The fun , satifastion and the use it will get ... PRICELESS... Link to comment Share on other sites More sharing options...
Guest Darrian Posted March 13, 2012 Share Posted March 13, 2012 I would put a pic up but for some reason it won't upload ? Link to comment Share on other sites More sharing options...
Guest Eddy Posted March 13, 2012 Share Posted March 13, 2012 (edited) Sounds like a good mod, nice work! Hmm what does it say when you try to upload it? Edited March 13, 2012 by Eddy Link to comment Share on other sites More sharing options...
Guest Darrian Posted March 13, 2012 Share Posted March 13, 2012 image is now in the gallery Link to comment Share on other sites More sharing options...
Rusty Strings Posted March 13, 2012 Share Posted March 13, 2012 very nice Darran. One thing I did to mine was fabricate some feet from MDF that mounted on the perspex to allow the scope to be stood on it's end without balancing on the fan. Link to comment Share on other sites More sharing options...
Daz Type-R Posted March 13, 2012 Share Posted March 13, 2012 Sorry bit baffled. How does blowing air up the OTA make the view better? I thought fans were to cool the scope down quicker, but once at the ambient temperature then the view should be the same? Saying that though, well done, nice job! Link to comment Share on other sites More sharing options...
Brantuk Posted March 13, 2012 Share Posted March 13, 2012 It removes warm air currents Daz and the squidgy views that go with it. Keeps the tube cool inside Link to comment Share on other sites More sharing options...
Daz Type-R Posted March 13, 2012 Share Posted March 13, 2012 It removes warm air currents Daz and the squidgy views that go with it. Keeps the tube cool inside But I thought thats why you let the scope cool first, to get the inside of the OTA to the same temp as the outside, thus removing any warm air currents? Link to comment Share on other sites More sharing options...
Brantuk Posted March 13, 2012 Share Posted March 13, 2012 Absolutely Daz - the fan helps it cool quicker and keeps the air flow steady and consistent - just standing close to the scope, body heat can induce air currents that affect the view - it also helps prevent moisture forming on the primary Link to comment Share on other sites More sharing options...
Daz Type-R Posted March 13, 2012 Share Posted March 13, 2012 (edited) Ahhhh thanks for that Kim, pardon my ignorance. Would you say then it is a worthwhile mod for us dob owners, I was going down the dew control system next but now wonder if I should be running the cooling fan option? How do you power the fan, can it run off a baz battery? Edited March 13, 2012 by Daz type-r Link to comment Share on other sites More sharing options...
Brantuk Posted March 13, 2012 Share Posted March 13, 2012 You can run the fan and dew heater from a baz battery no probs. A secondary dew heater is a must on even slightly moist evenings - at the right temperature it'll keep the mirror just above ambient and stop the dew forming. Any heat coming off will be blown out by the fan. We were all there learning at one time matey - so no probs with any questions Link to comment Share on other sites More sharing options...
Daz Type-R Posted March 13, 2012 Share Posted March 13, 2012 Any chance of a step by step guide for the electronic inept Link to comment Share on other sites More sharing options...
Brantuk Posted March 14, 2012 Share Posted March 14, 2012 Wish I could but I'm no electrician - I get all my sparky stuff ready made. All I know is long amp hours in a battery are best, most astro stuff is tip positive, check the total amp hours of all devices divide nicely into the battery amp hours to give you a good long session, keep batterys well charged. You'll need a secondary heater and a two channel controller and a fused supply (5amps should be enough). If someone here can't advise on wiring up a fan then Maplins will Link to comment Share on other sites More sharing options...
Rusty Strings Posted March 15, 2012 Share Posted March 15, 2012 Darrian, is your fan blowing or sucking? My sucks (no pun), and I do find that it draws dewey air down the tube and deposits it on the primary Link to comment Share on other sites More sharing options...
BAZ Posted March 15, 2012 Share Posted March 15, 2012 As Pat has said, what you need is total air movement across the mirror, there is a boundary layer of air that sits right on the mirror, and this causes it's own mirage type distortion. If the air flow is too fast it creates a vortex over mirror, and the rest just blasts past and out of the tube. I put mine on full blast for about half an hour, just to get cool air into the tube, and then with a speed controller which came with the scope, turn it down to minimum, which is barely turning. This seems to work fine, and if I turn it off, the image slowly starts to degrade, turn it on and it's back to good viewing. Link to comment Share on other sites More sharing options...
Guest Darrian Posted March 15, 2012 Share Posted March 15, 2012 Darrian, is your fan blowing or sucking? My sucks (no pun), and I do find that it draws dewey air down the tube and deposits it on the primary John .... Mines a blower not a sucker ... Link to comment Share on other sites More sharing options...
Guest Darrian Posted March 15, 2012 Share Posted March 15, 2012 Pat.... The fan i use is obviously a 12v 120mm, The base that it sits on covers the bottom of the tube so no air escapes and is directed straight up the tube, On the side of the fan is a speed controller and approximately 20 minutes ago i tried the same experiment with a very long length of drinking straw.. I also found that on full speed the smoke sits for a while in the centre of the mirror , intimating that there is no or very little current being pulled over the mirror , When i turned the fan onto low power the smoke disapates nicely across the mirrow showing that there is a gentle current of air being pulled over the mirror to keep it at ambient temperature. The morale of this story is ... whack it on full power before you use the scope to assist with cooling down and then whilst in use , knock the speed down to keep it stable . Link to comment Share on other sites More sharing options...
Rusty Strings Posted March 15, 2012 Share Posted March 15, 2012 I must try this myself, I'll need to hire a smoker. Never thought I'd say that. Link to comment Share on other sites More sharing options...
Brantuk Posted March 15, 2012 Share Posted March 15, 2012 Buying scope fans can seriously damage your health and that of others around you !! lol. This has been a very useful thread - especially as I'm about to rig a fan on the 300P - thanks guys Link to comment Share on other sites More sharing options...
Guest Darrian Posted March 15, 2012 Share Posted March 15, 2012 We aim to please .... even if i ain't got a clue what Im talking about lol Link to comment Share on other sites More sharing options...
Guest Darrian Posted March 16, 2012 Share Posted March 16, 2012 Mate... Im never offended.... it was a good test and worth noting for future fan mod Link to comment Share on other sites More sharing options...
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