Variable speed mirror fan

[matt]

Hey folks.

Had a bit of spare time on my hands with the cloud and rain over the last few days.

Decided to mod the newt and attach a mirror fan.

Made use of the useless back plate which normally seals the back of the SkyWatcher 8" and attached a computer fan and Dork Smith 12v variable speed drill unit.

Also wired a socket to power the unit from a cigarette lighter adaptor plugged in to my 17aH powertank.

Came up OK, if I say so myself:thumbsup:

Looking forward so seeing the result when it's working on the scope.

[Lester]

Is the fan sucking or blowing on the mirror?

[matt]

Lester

The fan's blowing ambient air onto the rear of the mirror, up into the tube.

It'll also help with removing the boundary layer from the surface of the mirror.

I decided to follow conventional wisdom on this one, although I am aware there are various schools of thought.

Will try it out and see how it performs.

[Lester]

Thanks Matt.:thumbsup:

[matt]

No worries Lester.

Asimov will be proud of my latest contribution to the "home made" club.:)

[davidpretorius]

that is a first class job.

problem is there are not enough wires hanging off and shards of metal for cutting your hands on!

seriously mate, you need too go back to "she'll be right" classes and make your projects more slap dash.

I am consoling asimov as we speak, he is having a hard time coming to grips and clean and tidy you have been. This is really unfair Matt, think of your mates next time!!!


Top work!!

[matt]

Cheers Dave:lol:

[asimov]

Geez mate! Thats pretty neat!.....But it ain't made of bits of cardboard N' masking tape N' so forth.....:(

Na! thats good mate! Top idea to have it variable speed, great job! :thumbsup:

[matt]

Yeah. Wanted the variable speed Asi.

Figure I'll have it fully cranked to cool it quick and then maybe turn it down to maintain temp?

Sorry it's such a neat and tidy job. Like I said I had a few days to work on it. So I smoothed off a few edges here and tucked away a few wires there.

I think I've watched too many episodes of Backyard Blitz!!!!:lol:

[Starkler]

Can I ask how you made the hole for the fan?

I made my disk from plywood and borrowed an adjustable single arm hole cutter and did it in a drill press.

[matt]

Mate.

Just took the plain (uncut) circular back plate to a friend's place who has a drill press and we used a circular metal cutter.

Of course, I'd pre-measured and marked the plate for the fan hole (72mm radius) and collimation screw holes at the edge (180 degrees apart).

Also had to drill holes for securing the fan to the back plate, but that was all there was to it. Pretty simple, actually... when you've got access to the right tools or a mate with a "Bloke's Palace" for a shed!!:lol:

[davidpretorius]

as tim the toolman would say....ugh ugh ugh

[matt]

OK. Here's the follow up.

Got a few small breaks in the cloud last night between 7-30 and 9pm.

Had the fan on full blast for about half an hour before and turned it to 1/3 speed during observing and all I can say is WOW!!!!!

Even with very average seeing and Jupiter at only 30 degrees above the horizon I could very clearly see a difference in the view. More subtle detail visible.

But the real difference was noticeable when I slewed to stars. Never had them quite so pin-sharp before, even in the 5mm Vixen LVW (200x). Could even make out the one or 2 fainter diffraction rings around the focused stars.

Alpha Cent and Acrux both very crisp.

If that's what they look like in average conditions I can't imagine what I'll get in good to very good seeing:eyepop:

I'm shocked. Honestly. I didn't think a mirror fan would make such a difference on a 8" scope.

Happy. So happy.

[davidpretorius]

fully recommend spending $30 + $5, get a digital temp sensor with dual sensors from dork smith and for the $5, some thermal paste and stick the sensor at the end of the wire 1/2 up the side of the primary mirror.

that way, you will kno for sure when your primary is within a degree of ambient.

next trick is to see if you can split antares into its blue brother. needs great collimation, good seeing and ambient mirror. it is a good test!

well done again on this one!

[bird]

Matt, if you've got a way to cool the primary then the best images will be had with the primary cooled *and* no airflow in the tube to cause currents - i.e. with the fan off and the bottom of the tube closed off.

But if the mirror is not quite cooled to ambient then you'll have to leave the fan running to keep breaking up the boundary layer and/or leave the tube open at both ends to help circulate air.

You should try some experiments...run the fan flat out for a few hours and then switch it off entirely for a test. If the primary has cooled down to ambient then all the air trapped in the tube will become stationary, and Nice Views will result :-)

If the fan arrangement you have now isn't enough to properly cool the mirror (and you have to go the temperature sensor route to really find this out) then you can go for the peltier-assisted cooling without too much hassle and that will certainly do the job.

cheers, Bird

[matt]

Thanks Dave.

I'll get a hold of one of those temp sensors and do as you suggest. It's the next logical step on the path you've already well and truly sprinted down!:lol:

Where do I get thermal paste, by the way?

And I'll accept that antares challenge, even though I'm only shootin' with an 8". Should be do-able, right?

Also, good advice Bird. I'll try it next clear night flat out ... and then turn it off when it's time for viewing/imaging.

Thanks guys:thumbsup:

[davidpretorius]

dork smith should have it or jaycar i know does!

i used my 5mm lv vixen with the 10" and asimov has done it with the 5" or 6" refractor so i reckon you should be able to.

the main thing here is to know when has the ambient stopped dropping. Canberra sounds alot like tasmania in terms of moderate days, coool cool nights. so knowing the ambient temp is crucial for where you live

[iceman]

Looks great Matt. Something I really should be starting on, too.

I'm off to D.ick smith today to get a thermometer.

[matt]

Thanks Mike. Does your scope not have a fan?

[iceman]

Nope, my scope has nothing in that area :) Although at the moment it's permanently setup on the lawn with the platform aligned, the scope on top and a cover over the whole thing. So it's cooling down from the moment the sun goes down :)

So first step is the thermometer to tell the difference (if any) in temperature between the mirror and ambient, then a cooling fan, then a peltier.

[matt]

Wow. Well, there you go. Your images are a glowing testimonial to natural (passive) cooling and favourable ambient conditions.

Should be interesting to see what, if any, improvement a fan and temp experiments bring to your images.

Good stuff:thumbsup:

[iceman]

Ok, I went to d.ick smith at lunch today and picked up some goodies.

Got this 9cm 12v rotary cooling fan (http://www.dse.com.au/cgi-bin/dse.storefront/4456e4fa08fb90362742c0a87f9c072a/Product/View/Y8498) for $20.

I asked them for a variable control box, but they didn't have any. This power house store wasn't as big as some others I've been to in terms of electronics gear, so i'll try the one close to home and see if they have it.

Where did you get yours from Matt?

How is it powered?

How is it wired up to the power and the fan?

[davidpretorius]

bunnings sell aluminium sheet that is .6mm that you can quite easily but into a disc if you want to seal the bum of ya scope

[matt]

Here you go Mike.

http://dseau.resultspage.com/search.php?sessionid=4456e4fa08fb90 362742c0a87f9c072a&site=&w=K-3070&I1.x=11&I1.y=10

I run mine plugged into a SkyWatcher 17Ah 12V powertank which I bought from MyAstroShop.

Cigarette lighter adaptor plugs in to Powertank ... other end plugs in to base of DC Motor Controller Kit using a socket I also bought from D.Smith and wired to the controller kit's circuit board.

The black plastic box housing the motor controller kit is bought separately. You just need to make a few holes for the speed knob, the power-in plug and the wires connecting the fan to the controller kit.

And Bob's your mother's brother!!!!

Hope this helps:)

[Orion]

Well done Matt with your fan, I'm just wondering can you use one controller to control more than one fan?

[matt]

Not sure Ed?

Would that not increase the load through the controller and cause a few probs?

Wouldn't the fans possibly not get the volts they require?

Worth an experiment.... for another time;)

[gaa_ian]

Thats great Matt, do you have the Catalog numbers for the DSE components you used ?
I buy from DSE all the time online & have an account so I get good prices.
This would be good for my 10" dob in the dry season!

[RAJAH235]

Ed, fwiw. The 12 volt fans run on around 170 mA, so you could use 2 or 3 fans with no trouble on the one PWM controller. BUT, because of their diff characteristics, you might find that one requires more 'power' than the others. (do a bench test to see if they all run @ about the same speed setting).
Just watch the total 'on' time tho, if battery is also used to power your t'scope. (Best with a separate battery).
HTH. :D L.

[iceman]

Ian, the catalogue number for the controller is K-3070 (in Matt's link).

The catalogue number for the fan is in my link above.

[matt]

Just beat me to it Mike!

By the way, how'd you go? Did you get the speed controller kit?

[Orion]

Thanks for the info Laurie,

This is the configuration of the fans that I am planning on using the controller on.
There are three 4cm fans and one 12cm.
I'm guessing I might need two separate controllers?

[iceman]

Will check DSE again today.


Wow Ed, that looks great! Is this to go on your 18"?

[Orion]

A 24" Mike that I am in the middle stages of designing.

[matt]

Oh yeahhhhhh!!!

That'd certainly be a little too much puff for my 8" newt!:lol:

[iceman]

Nice!

[iceman]

The DSE here doesn't stock the K-3070, but it is at the Gosford store (near home), so i'll go and get one soon.

[astro_nutt]

I opted for the "make it out of whatever" method..until I have the proper stuff..I used packing tape to secure a 3 volt motor onto a 30cm length of heavy duty electrical wire then secure this with more packing tape to a lantern battery..I found a fan from an old hair-dryer...attach this to the motor..a clothes peg for the switch...and it works!!..I just point the fan to the primary and remember not to move the scope while I have it going!!!...cause it does make horrible noises if you do!!
I like the idea of have a variable speed fan though..
Good one Matt!!!
Cheers!

[stringscope]

Hi Matt,

That is a really nice neat and simple mod. Well done!

Cheers.

[matt]

Thanks Ian.

And you've just reminded me it's almost time to renew my CAS membership and also to give you a much belated call to get together and check out those Konigs in my 9.25 and just generally catch up:)

[stringscope]

Hey Matt. I thought you had lost interest in the Konigs!!

Yes, Shirley will be chasing us for our CAS membership renewals pretty soon.

Cheers,

[matt]

No. haven't lost interest.

Just lack of time and opportunity ... and too many other costly distractions:lol:

[iceman]

Ok well I went shopping again yesterday.. my Dad was down from Bellingen for the day too, so used his handyman skills to help me :)

Bought the K-3070 controller and a kit box from D.ick Smith, and some aluminium "stucco pattern" sheet from Bunnings (they didn't have plain). Oh, Matt didn't tell me the K-3070 was a "put it together yourself" kit - I was hoping it would all come pre-built!

So I had to buy a soldering iron and some solder too.. this will be fun, haven't done any soldering since 1988! :)

Anyway, made the mounting plate for the fan.. cut a 285mm circle out of the alumium, a 90mm hole in the centre for the fan, and 6 holes to go over the collimation and lock screws. All done, all looks and fits great.

The fan is in place, but I haven't had a chance to build the controller kit so the fan isn't powered yet. I also haven't taken the mirror out yet to clean it and fit the outdoor temperature sensor - i'll do that tomorrow if I get time.

It feels great that this is finally all coming together.

[davidpretorius]

i notice from your signature, you have a canon thingy, does this take photos.

i am sure one of the moderators can help you to upload your photos of your modification.

also, please send a write up to the site owner, make sure you include any injuries incurred and laughs from the wife upon showing her your handiwork!

oh and references to jobs around the house that you could have accomplished with that extra set of hands!!!

in all seriousness, did your dad have a look through the scope???

[asimov]

Stay tuned for the logical answer folks! :)

[iceman]

Of course! :) Will post more about that in another thread.. :)

And will post some photos of my mods tomorrow or Tuesday.

[matt]

Yo Mike!!!!

Check out my link for the speed motor "kit".

You'll find the word "kit" .... in the item description headline in bold blue.

It's a kit. **** Smith sells kits. Sheesh!:lol: