Fan or No Fan that is the question

[spaceboy]

Hi Guys from a novice who really has no idea.

Looking in to doing some mods. Totally understand the need for flocking and the lazy susan bearing side of thing. Although some of the searching on the web has returned pic of some messy flocking efforts. Would a mess of a flock matter as long as the original paint is covered?? And I asume the bearing are a direct replacement for the teflon pads??

Any way back to the point.... if the telescope is stored in an observatory do you still need a fan? Also what would be best a fan? one that moves plenty of air quick or one that dosn't. Some I have seen will move upto 31 CFM and others only 10 CFM.

For journeys out to the sticks I take it you only need to use the fan once to cool the mirror during setup (power supply reasons to be considered) or is it to be used during observing. If it is to be used only once is it puerly just so you speed everything up ready for viewing?

Are there any detailed walk throughs on the forum with pics and they like for doing mods.

And finally guys (to your relief ) is it work doing any mods if you are in a light polluted area. I ask as I as I'm sure most of you do have one stationary in an observatory and one for on the go it could become exspensive to do to mods.

[Doc]

My 16" dob has one mighty large fan on the back but I have never used it. The reason being it is really not a grab and go type of scope, to use it requires planning ahead so if the weather report looks good the scope is moved outside 3 hours before use and covered with a waterproof cover.

This way it reaches equal temperature naturally and there is no need for the fan.

If your scope is in an observatory that has no heating I would imagine your scope would be very close to ambient temperature anyway.

[johninderby]

Fitting a Lazy Susan bearing isn't quite as simple as just replacing the Teflon pads. Now the problem is that the scope moves so easily that it will be unusable and the slightest touch will leave the scope spinning round by itself. You will have to add some "friction pads" to give enough resistance. The old teflon pads mounted on blocks to give some drag will do.

I've found after some experimenting that the cooling fan should be a lot smaller than you would expect. The air being blown across the back of the mirror has to move slowly enough so that it can pick up some heat. If you blast the air across the back of the mirror it doesn't have time to pick up that heat. Case in point, my 14" OO dob uses just one 60mm low speed fan which is extremely effective in cooling down the mirror.

If you have a low-expansion glass mirror you probably won't need to keep the fan running while observing as it will be able to track the temperature changes without assistance. Scopes with plate glass mirrors may benefit from having the fan running while observing though.

John

[Talitha]

My 16" LB is stored in a shed at the Starpad, the walls aren't insulated but the roof is. The ventilation is excellent but even so, the inside of the shed has been up to 36C a few times on hot sunny summer days. Even though the scope was taken out to cool several hours ahead of time, i used the fan anyway, just for good measure.

Another thing i do regarding fan use is to keep checking the outside temp. If it's dropping more than 5 degrees (F) in less than 1/2 hour, i run the fan for a bit just to make sure the mirror's temp keeps up with the drop.

[spaceboy]

Thanks guys & girls. Having accumilated several telescopes over the years I put bad viewing down to having a **** telescope. It is only since joining SGL site that I found that in fact everyone has at one point or other made some kind of mod for improvement. You would think there was a book or something out there to help the beginner make these improvements. From what I have read the improvements make the whole experience so much more pleasurable. Maybe if there was a book to help beginners then there would be more amature astronomers. As with anyones first experiences of looking through a telescope, it's never quite how you had it pictured, and if the picture is washed out because your telescope is missing them little tweaks then what chance do you have.

[Chris H]

There is a book it's called 'Astronomy Hacks' and it is particularly excellent if you own a dobsonian telescope and want to do some mods.

[Astro_Baby]

On the subject of fans there has been a few threads one here - most recently here http://stargazerslounge.com/diy-astronomer/112372-cooling-fans-skywatcher-200p.html

Theres also an excellent article on the subject here Telescope Optics Topics

Hope thats of some help.

[spaceboy]

On the subject of fans there has been a few threads one here - most recently here http://stargazerslounge.com/diy-astronomer/112372-cooling-fans-skywatcher-200p.html

Theres also an excellent article on the subject here Telescope Optics Topics

Hope thats of some help.

Yes I had seen this thread and found it useful but there is no straight forward way of mounting a board to the back of my 250 dob with out doing more messing that I would like to risk. The 200p finished product is great but I still don't now know how step by step how it was done. There was no mention where you get the parts like the vari control switch from so I'm still stuck and not sure what parts have proven best for the job. I think there was mention of Maplins and I took a visit yesterday butthere is so much stuff to choose from I didn't know where to start. I am concerned about the tidiness of cables dangling etc

The artical on the optics was great thanks Astro_baby and I will have to search for that book Thanks Chris

[johninderby]

PC fan speed control like this one will do the job.

http://cgi.ebay.co.uk/Gelid-Solutions-Manual-Fan-Speed-Controller-/220658294315?pt=Computing_ComputerComponents_Fans_Heatsinks_SR&hash=item3360425e2b

One easy way to mount the fan is to fit it into a disk. Then replace three of the screws in the side of the tube that hold the mirror cell with small thumb screws. Then you get some elastic shock cord and tie it to the disk with the fan and tie loops in the cord that fit over the thumb screws.

Here's a photo of this fan mounting arrangement that I used with an Orion 8" newt. This was before I discovered that a smaller fan would have been better for cooling.

John

[spaceboy]

Thanks John. Just the man I've been looking for. Have been checking out your thread Low profile focuser NICE!! would like to know where you got it fo £100 though! Like the handle on the OTA where did you get it from and did you have to plate inside for strength? (like view finder mount plate) Don't suppose there is a thread from when you fitted it? I think you have the same dob as me?? have you upgraded the base ie: lazy suzan bearings. I am looking into how to make some sort of braking system so to control the scope from just swinging around.

[Moonshane]

I agree with John, a small fan would be fine with most scopes. I have an 80mm fan on my 12" and will have a 35mm on the 6" when I get around to the mod. the 12" fan runs almost silently at 3.5v for observing after being on 12v at full pelt for an hour for the cool down.

[johninderby]

Which focuser? There was my review of the SkyWatcher Low Profile crayford, but in another thread I had installed one of the Telescope House Revelation crayfords. I see that TS have that focuser on for £89.99 at the moment. Then you just need one of the SkyWatcher mounting bases from Scopes'n'Skies astroboot section for £2.00.

http://www.telescopehouse.com/acatalog/info_SNT30_A.html

The handles came from WDS Ltd

http://www.wdsltd.co.uk/products/Machine-Parts/Handles/WDS-8532-Handle-177/

I used large washers that I got from Focus DIY on the inside of the tube when I bolted the handles on.

http://www.focusdiy.co.uk/RepairWashersZincPlatedm8X40mm10Pcs266406?category=nuts_bolts_washers

I used some "Slide Glides" that were intended for fitting on the bottom of chair legs for the friction pads on the base when I fitted the lazy Susan.

http://www.focusdiy.co.uk/dispatcher?search=glide

John

[spaceboy]

THANKS JOHN

I was on about the SW low profile duel speed post but I will look into the other. Found another post that says there is an upgrade 10:1 part for the standard crayford which is £59 so in the interest of saving them pennies I may go with that?? I don't truely understand the difference of the standard duel speed and the low profile anyway other than size

Having read through some of the links in the post I decided to go with a fan and ordered the parts going with the half hearted effort of fixing it to the pre drilled holes but plan to add the vari switch and motorcycle battery for full range of power. No idea what to do with the dangling wires so will have to live with it

Have an idea of a breaking method for the lazy susan bearings so if all works out I will have a go at doing a detailed thread. I like the idea of the chair feet though. Pictures are a great help Thanks.

[johninderby]

The replacement focusers are much better quality with less slop in them, are smoother and also use compression rings instead of just screws to hold your eyepieces. The dual speed upgrade with the standard focuser would help but the resulting focuser still won't be anywhere near as good as a replacement one. At the price TH has their focuser on at now I'd definitely go for it.

The one weakness of the SW low profile is that the built in extension tube isn't that solid an arrangement and the TH with a separate extension tube works better.

If you ft the fan to the pre-drilled holes remember to use some washers to leave a gap under the fan housing to let the air flow over the whole mirror.

With the chair glides I put some thin disks of polythene cut from a milk bottle under them to get the height just right. You'll have to experiment a bit to see how many you'll need.

John

[spaceboy]

I was more concerned with vibration Acoustifan Anti Vibration 80mm Fan Gasket on eBay (end time 25-Sep-10 23:58:01 BST)I never give a gap thought. It's all such a steep learning curve. You wouldn't believe I've had a telescope for 6 years. Always put bad viewing down to light pollution. Never thought after paying out money on a scope I would be putting my hand in my pocket so soon after. I have just ordered the biggest bearing I can for the base so just the waiting game now to see how things turn out.

[johninderby]

I used a couple of soft rubber O rings in-between the fan and the mirror cell with another rubber O ring in-between the bolt head and the top of the fan housing.

You could also use some pieces cut from neoprene rubber tube.

John

[leedseagle]

I agree with John, a small fan would be fine with most scopes. I have an 80mm fan on my 12" and will have a 35mm on the 6" when I get around to the mod. the 12" fan runs almost silently at 3.5v for observing after being on 12v at full pelt for an hour for the cool down.

Hi there

I also have 12" Dob (skywatcher) and am about to get an 80mm fan.

I have four screw holes below primary mirror cell that would be perfect to attach, is this where you have attached yours?

All the best

Leedseagle

[Earl]

I Would recommend a larger slower rpm fan as these are more efficient.

A Noctua would be a good choice, these are designed for Silent running HTPC systems.

[Moonshane]

hi there Leedseagle

you can mount the fan there but I was always concerned about vibration being so close to the cell (in fact mounted on the cell).

I have already changed the 40mm fan I installed on my 6" dob as it really vibrated quite a lot and did not shift much air. I have got a 60mm one now - much better and actually louder but with less vibration! work than one out.

see http://stargazerslounge.com/diy-astronomer/115026-ongoing-mods-my-orion-optics-uk-6-f11-planetary-dobsonian.html for how I mounted one of them and http://stargazerslounge.com/diy-astronomer/109577-latest-dob-mods-fan-balancing-weight.html for the larger dob. the first link gives more detail.

others have done it differently by using a 'hair bobble' (not the fancy ones with feathers just the plain black - unless you like the fancy ones with feathers) and some bolts in the side of the tube etc.

[leedseagle]

PC fan speed control like this one will do the job.

http://cgi.ebay.co.uk/Gelid-Solutions-Manual-Fan-Speed-Controller-/220658294315?pt=Computing_ComputerComponents_Fans_Heatsinks_SR&hash=item3360425e2b

One easy way to mount the fan is to fit it into a disk. Then replace three of the screws in the side of the tube that hold the mirror cell with small thumb screws. Then you get some elastic shock cord and tie it to the disk with the fan and tie loops in the cord that fit over the thumb screws.

Here's a photo of this fan mounting arrangement that I used with an Orion 8" newt. This was before I discovered that a smaller fan would have been better for cooling.

John

hi there

i've just bought an 80mm fan for my 12" skywatcher and would like to attach it with the hair bobbles and disk. i was wondering where did you get your disk?

All the best

Leedseagle

[Moonshane]

just make one out of a suitable material - you could use cardboard covered in insulation tape, or buy some 'plastic card' type material from eg Hobbycraft. some people have used a clock face of a suitable size, maybe look in a junk shop? anything will do really. cut a hole for the fan and the 'bobbles' and you are away!

[leedseagle]

Thanks for the advice I've used cardboard method with thumb screws from my spare focuser works great

All the best

leedseagle