SCT cooler

[matt]

Hi guys. Need some opinions/advice. I've recently bought a Lymax SCT cooler for my 9.25. Prob is, the dew in Canberra's as bad as the temp differentials. I've had a read of the instructions for the cooler and it says not to use the cooler in extremely humid conditions or when dewing is heavy. Well, that's evey night in winter in canberra! I'm guessing it's to avoid potentially blowing moist air into the scope tube, but it effectively rules out using my cooler. Humidity at night here starts around 50% and frequently climbs to 90%+ by 4 or 5am.... every night. What do you think? Still use the cooler? Your help much appreciated.

[[1ponders]]

It's a hard call to make if your trying to get somewhere near ambient. I'd think very carefully about it matt. I have first hand experience of what can happen to your SCT in the presence of high humidity. Fungus fungus everywhere.

I know your trying to get the temp down, but I was given some advice the other day from someone who is in a position to know just about everything there is to know about fungus and scts and his advice was to seal the scope completely with a dust/humidity filter. Unfortunately that would preclude using the Cat cooler.

I know that doesn't help you but it's important info you should be aware of.

A quick question about how you use the cooler. Do you only need to use it at the start of the night or do you need to repeatedly use it to keep bringing the temp down?

[matt]

Thanks Paul. To your question. I think most use it early on to quickly bring the scope to ambient and then might give it another run a little later to help the mirror track any further temp change/s??? Anyone else care to comment?

[matt]

I guess the next question is: what level of humidity (%) is acceptable for Cat Cooler use???? Gee, if it wasn't tough enough with dew and heaters for the corrector plate etc!!!!!!!!!!!!!!!!!!!!

[asimov]

Yes, I care to comment. I had a practical demonstration of what happens when using a cooler in heavy dew situations/conditions. Call me stupid (most do, lol) But I should have thought about this from the get-go when I built mine. Used it for about 15 mins the other night & It suddenly dawned on me that, ok, if this cooler is sucking in air from a dew laden atmosphere.......??..........I grab a torch & shine it down the OTA........DEW!! On the inside! On the corrector & Primary. Luckily, only a very light coat of dew (due to 15 mins use) but had I kept using it for 2 or 3 hours??????? I don't wanna think about it. I haven't used the cooler since.

Luckily it was the only very dewy night we've had here. No experience with high humidity as yet, but yep! Don't use it on very dewy nights!!

I'm now trying to think of a filtering system for dew/humidity. Damn!

[matt]

But where do you reckon the % humidity cutoff for cooler use might be, Asi?

[asimov]

To figure that out, I'd have to find out the dew point for the...hell, not sure what night it was..thursday or friday. Is there a website for looking up this info I wonder?

[matt]

No mate. Keep it simple. What would you consider an acceptable humidity level for safe use of the SCT cooler?? Right now we've got 35% humidity in Canberra. That's fine I'd guess. But 60%+ ... maybe not

[asimov]

Depends on the filter in the cooler, I'd imagine. It would have to filter out Xamount of moisture. (but then what happens when the filter gets wet from the intake of moisture.....)

I'd only be guessing here...45-50% perhaps?

[asimov]

The other alternative is to regularly check for fogging of the optics. As soon as it starts, thats it. turn the bugga off!

[matt]

Yeah. Reckon you're right, and best to err on the side of caution. Super caution!!!!

[[1ponders]]

There is a problem with working out when not to use the cooler depending on outside dewpoint. If you vent your sct with the cooler at 6:00 pm and the temperature is around 25 deg and relative humidity is only 50% you won't have a problem then. The problem starts to occur when the temperature drops. As temperature drops the relative humidity will go up, until you get to the dew point. Only natural.

But what is happening inside your SCT. You have put air in there at 25 deg 50% relative humidity, as the internal temp drops your internal RH will go up and you will get to a point (dew point) where the moisture that was suspended starts to precipitate out and settle on cooling surfaces, particularly glass surfaces.

[asimov]

I'm thinking......Airconditioners. They not only cool the air, but filter out moisture/humidity/water vapour. Someone please correct me if I'm wrong here!?.......lol!! Ducted airconditioning up the spout of an SCT telescope! YEAH! :rofl:

[casstony]

Matt,
have you considered exposing the ota internals to a desiccant when the scope is not in use? I use a film container with desiccant packs inside it inserted into the 1.25" eyepiece holder - the container has holes drilled in it. I think there are commercial solutions available too.
-Tony

[matt]

Thanks for the advice guys. Will be grabbing plenty of desiccant packs and keeping them close to the OTA during storage from now on. Will also be keeping a close eye on all the humidity/dew point indicators. Cheers

[davidpretorius]

cool it first, bird believes the peltiers dry the air as well.

[[1ponders]]

Be careful with desiccants like silica gel. The advice I was given the other day came from Bintel. I thought of using silica gel to control my fungus problem. I was also advised to be careful using silica gel because of outgassing of the gel. This can coat the inside of the scope with a really fine powder that will stick to any surface.

I know this isn't help you with your problem matt but I'd rather be known as a doomsayer than see you suffer from something that is avoidable.

The air conditioning sounds like a great idea. Do you have an airconditioned room somewhere in the house? Where do you keep your scope when you are not using it?

[[1ponders]]

What we need is someone like bird to develop a system similar to his mirror cooling

[matt]

Absolutely Paul. It's amazing it hasn't already been done! And don't worry about pointing out potential problems. Like you say, better to be forewarned than forever sorry. Much appreciated.

[davidpretorius]

i had given some ideas to asi and paul (rumples on this a few weeks ago)

take that peltier off the **** smith fridge, enclose it around the base of a cat cooler or asi's milled version. have an internal temp sensor inside and bobs your uncle

[matt]

The idea's not a bad one but I've yet to see it actually done (on an SCT) to anyone's scope around here? For starters, how would you "enclose it round the base of a cat cooler"? You seen one of these in the flesh Dave? Also, where would you place the internal sensor? I'm not in a blinding rush to pull my SCT apart. Not to mention the actual construction itself. I'm not trained or experienced in any way in anything electrical or technical. I can, however, write you a pretty good feature magazine article or read a news bulletin! What's simple and straight-forward to you is a little daunting to some of us Dave.

[casstony]

I haven't used desiccant in my scope very often but there doesn't appear to be any residue from outgassing. I use the small packs from inside pill containers and place them inside the film canister. The bags used in these packs appear to be very dense and tough - maybe thats enough to filter any outgassed material?
-Tony

[asimov]

I can't get hold of these peltier coolers in my area! I'm out in the sticks here. No problem for me building a system. The sensor will go on the end of the pipe on the cooler Matt. When the coolers inserted, instant internal temp readouts.

[davidpretorius]

ok, asi or mick pinner with his skills would have to make it, but it you get asi homemade tube for blowing air up the tube and into the cavity of the c9.25.

instead of drawing air from the surrounding air, you attach the peltier / heat sink to where the fan is and enclose it so that only cold air from the cold plate is sucked up the tube.

so imagine this heat sink / peltier on the end of asi's cooler. (http://www.iceinspace.com.au/forum/attachment.php?attachmentid=10871&d=1143619121)

have you a picture of the lymax. is it similiar to this one of rumple's

[davidpretorius]

i have not seen it done, just an idea from watching rumples at work and from talking with bird and making my own cooling system.

Steve Mogg is about to do something for reflectors, so may go done this track for sct's.

Does anyone know if you can get an electronic moisture reader. It would be great to read the moisture coming off a zero degree cold plate

[asimov]

The one that rumples has in his hands is no different than my home made job, only mines made of bits & pieces but with a bigger fan.

[Lester]

Great topic chaps, The peltier will only dryout and cool a small amount of air; so the question should be what sized peltier is needed to cool and dryout the required air flow from the fan used.

Sorry I don't know the answer; but perhaps someone at www.techbuy.com.au (http://www.techbuy.com.au) can help. Good luck

[asimov]

I think ducted air from a controllable source. ie:cooled/dehumidified/particle filtered air.

[[1ponders]]

It sounds like us SCTers need a little box like an esky that we can put our scopes in and cool them in there. That way we would have greater control of the temperature and humidity. Once the scope reaches ambient we can then mount them. Bit hard for those with fork mounts though.

[Lester]

How about sucking air with your gadget from a camping fridge? Just trying to think of how to do it where there is no mains electricity.

[acropolite]

I reckon DP's on the money, the peltier being cool will condense moisture and dry the air before it goes into your SCT.

[asimov]

Believe it or not Paul, I think you've come up with something there!!!

A couple of years ago, I made this esky at work (out of sheet metal)....I reckon it will hold the SCT OTA no worries! Yes! OTA in sealed esky....controlled air from hypothetical source ducted into esky! I'm going to dig it out of the shed & post a pic of this esky I'm talking about......

[[1ponders]]

Yeah and minature airconditioned cool box. It will be important to match the internal with the external temp fall. One of my concerns would be that when the OTA is removed from the box it will becoming from a low humidity environment and moisture in the air will instantly start to condense on the OTA. There needs to be someway to prevent the external air from getting into the OTA. Condensation on the outside of the corrector plate isn't a prob, getting it on the inside would be a different story. Maybe that dust/humidity filter would work in that situation.

Few things to think about to solve this little problem

[matt]

Dave. My Lymax is exactly the same as Rumples'

[asimov]

Here it is. Inside dimensions: 1000mm L 500 W 450 D. Big enough to hold 2.5 possibly 3 slabs of beer :D Made 2 boxes, one 3.5" smaller than the other in all dimensions. Glued that white packing foam (1.75" thick) on all surfaces of the smaller box, Slipped the bigger one over the top. Even just to keep the OTA in it & leave it in a cool room all the time would have to help. I'd rather see it kept at ambient though somehow.

A normal bought esky would do just as well. Why not just cut a hole in the esky & mount a fan & peltier system to that? Have the scope sealed, naturally. If you could preset the temp to whatever you wanted, roughly to what your ambient gets down to normally in your area (here its about 6-8C this time of year) You could have it running 24/7 if you wanted to at home.

Food for thought.

[asimov]

Then again, why goto all that trouble with the esky/fan/peltier.....when theres a fridge available. He-he!

[asimov]

Now dumping a sealed finderscope in the fridge, lol

[asimov]

Interesting. The finder I put in the fridge I put in a ziplock bag. I took it out after nearly 2 hours in there. It immediately fogged up after taking it out of the bag in the house as you'd expect. But when I took it outside seconds later the fog burnt off the optics within seconds. I can guarantee its not as cold outside as it is in my fridge.

[[1ponders]]

You need to get hold of a couple of hygrometer to make a comparative measurement of relative humidity inside and outside. By the sounds of it, much more humid in the house than out, which at that time of night sounds pretty normal.