Dew on optics in a dome

[strongmanmike (Michael)]

Thanks for all the feedback guys much appreciated

The AG12 has a built in 12V tube heater moulded directly into the tube just in front of the primary, combined with the rear extraction fans and secondary mirror heater pad, I have no problem with dew during imaging sessions, not even on front corrector element that is exposed to the inside of the tube.

I had thought of leaving the tube heater on all day but it is 12V so batteries will go flat and I am not sure about leaving anything electrical like that on 24/7..? If I had mains power connected I could put its power supply on a timer and it might be the way to go, I could set it to come on for a few hours each day, likely in the mornings..?

So, until I have mains power I have ordered two rechargeable desiccant boxes designed for use in a much larger space than the inside of the AG12, I will place one in the tube after an imaging session and put the cap on the OTA, I will place a bag over the rear end of the OTA where the three fan outlets are and this will then become a fully enclosed space. When the box needs recharging I will just pop it in the oven and put the fresh one in the tube to replace it. I will also get a couple of the items Bob mentions and place them in the observatory.

I'll reassess as time goes by and should I get mains connected I will likely go down the dehumidifier on a timer option

Thanks again guys

Mike

[Tandum (Robin)]

I don't get any of this in my foam dome. My problem has always been keeping rain water out. That's what ya get when a technician does building work

[DavidTrap (David)]

Mike - what sort of desiccant are you getting.

I had some blue desiccant that could be recharged, but apparently the blue stuff uses cobalt and carcinogenic.

I bought some silica gel in 100g packets on eBay for $3-5 each. I've but a bag in every box of gear I have. They can be recharged in the oven, although I'm yet to do that - apparently you can weigh them and see if they need recharging.

DT

[Nico13 (Ken)]

Hi Mike,
A mate of mine (not on the forum) has used the electric blanket method for years and swears by it and his setup is in a plain tin shed with roll off roof.

[strongmanmike (Michael)]

Hi Dave, as per the link in my post, this one

Sounds like a good idea Ken but again having something electrical on all the time worries me a tad...

Mike

[Tandum (Robin)]

I thought people were installing these solar exhaust fans to equalise things.

[strongmanmike (Michael)]

Originally Posted by Tandum

I thought people were installing these solar exhaust fans to equalise things.

Yes they look good and I imagine this might be good for removing heat from an observatory but I wonder how effective it would be with reducing the internal humidity if the outside humidity is high...?

Mike

[kinetic (Steve)]

Originally Posted by Tandum

I don't get any of this in my foam dome. My problem has always been keeping rain water out. That's what ya get when a technician does building work

+1

Steve

[bert (Brett)]

Originally Posted by avandonk

Concrete absorbs water as it cures. In fact in dry conditions it is kept wet by ponding or spraying. The setting is an exothermic reaction so it can drive off much needed water for the chemical reactions to occur.

Bert

Where does all the water go that was in the wet concrete mix bert? Its released into to the air, in Mikes case into the dome, which was my point of my post. And this lessens over time as the cured concrete dries.

Its true that concrete keeping concrete wet will make it stronger, also water can be helpful in cooling the concrete in Higher temperatures, where the exothermic reaction heats the concrete as it hardens.

I have seen the effect of condensation first hand in building where the concrete is still 'green' ie not fully cured. Even with sisalation and other methods of condensation control, ends up raining inside every morning as the concrete releases moisture. This effect leesens over the next few weeks.

[DannyV (Danny)]

Hi All,
I'm running a small aircon duct from my room in the house with an internal fan to the dome that I'm building.
It used to be from my shed A/c for summer, but I'm changing it now winter's on the way.
The fan will have a speed control to just keep it ticking over, but i'll fill the little dome with enough room air. The dome will be sealed as much as possible - just leaking a bit here and there. My dome is made from 40mm polystyrene and silver foil.

[Logieberra (Logan)]

I purchased a Delongi dehumidifier from Harvey N in Fyshwick. I have it set on a timer, 'on' at 8-830 each AM. Surprising how much moisture it collects from the astro shed. Very effective after a night open to the Cbr air. Love it.

[strongmanmike (Michael)]

Originally Posted by Logieberra

I purchased a Delongi dehumidifier from Harvey N in Fyshwick. I have it set on a timer, 'on' at 8-830 each AM. Surprising how much moisture it collects from the astro shed. Very effective after a night open to the Cbr air. Love it.

Hi Logan

yes I will likely do the same if I get 240V connected...because we are renting and digging some long trenches though garden beds etc isn't realistic or appealing, I'm thinking of simply running an extension lead through a garden hose and leaving it out on the ground 24/7..?

Mike

[marc4darkskies (Marcus)]

Originally Posted by strongmanmike

... I'm thinking of simply running an extension lead through a garden hose and leaving it out on the ground 24/7..?

That's thinking outside the box ... errrr ... observatory! Frankly, a dehumidifier is the only real / complete solution to your problem. Otherwise your obs will be permanently dank. (always wanted to use that emoticon)

[mswhin63 (Malcolm)]

Originally Posted by strongmanmike

Hi Logan

yes I will likely do the same if I get 240V connected...because we are renting and digging some long trenches though garden beds etc isn't realistic or appealing, I'm thinking of simply running an extension lead through a garden hose and leaving it out on the ground 24/7..?

Mike

Hi Mike, I too live in a rental premises and I can't do anything below ground, even more so in my situation. I am investigating some low power ideas to get all the features including dew capture as well, I am hoping your consideration with the packet moisture collection products work out.

Mainly my solutions will be through solar power. I am not sure you have looked it this already but I hope to make it so that I can move everything along with the electronics as well. Maybe a idea to look at some auctions to get cheap panels. Or maybe the offers that are going around for cheap solar installations. Should be enough for an observatory. Mine will be designed around low power Beaglebone, Arduino and FPGA technology.

[Phil Hart]

We (the ASV) purchased a dehumidifier for our dome once we hit this problem. Once you take the plunge, you need a dessicant dehumidifier as standard models are not effective in cold temps. We got this one:

http://www.dampsolutions.com.au/stor...t-dehumidifier

Seems to be working well but have had to extend the hours of operation on the timer. It's a bit of a battle in Victorian conditions but it must be helping.

Markus.. how well sealed is your dome? We don't get ours down to 50% very easily but the problem is that it's 2 hours away so I don't get to check in on it very often, and when I am there it's clear and we've got the dome open and are imaging.

Mike.. I think you will have to get over your fear of living power on.. there's a lot to gain.

Phil

[marc4darkskies (Marcus)]

Originally Posted by philiphart

...
Markus.. how well sealed is your dome? We don't get ours down to 50% very easily but the problem is that it's 2 hours away so I don't get to check in on it very often, and when I am there it's clear and we've got the dome open and are imaging.

Not very well. But even on the wettest nights (dripping down the walls inside the dome after a session), everything is dry by late morning after buttoning up around 3:00am. It's also not very effective below 5 deg so I'm eying some of the newer models. Also during prolonged wet weather, it will humidistat off and on with it set at the driest setting (40 or 50%). I've been thinking of sealing around the door and the pier but that would leave the some gap around the dome circumference and the the slit so it would be only marginally effective at saving a bit of electricity.

[Paul Haese]

Clayton Bay is the dew city of the entire solar system. I gauged 100mm last year in dew. Summer and winter the only time dew does not occur is when the wind comes from the north. Totally bizarre. I use a dew heater on both scopes and that is all. Dew drips off everything. Next day I open up the observatory for a bit to get the heat in again and that is all I do. Nothing is rusting or corroding. I would not bother too much. Canberra is very dew too as Anthony and I have talked about this issue many time. Personally I would not bother with dessicant as you will be re-charging it every couple of days. Your gear is built for dew and will last out the dew better than you might think.

[strongmanmike (Michael)]

Cheers guys

Thanks Paul, yes, as I said, my dew abatement during imaging is working fine, it is just the coming and going of moisture in the closed observatory over time that I am concerned about, mould on the optics etc, I think tackling it in some way is probably worthwhile. You may eb right about the desiccant, we'll see


Mike

[strongmanmike (Michael)]

Well....I opened up tonight after last imaging a week ago and the focus was perfect, no adjustment needed, I did a goto the same target NGC 6164 and after a couple of short exposures and slews I was on frame within a couple of pixels, easy...bah, who needs plate solving

Observatory life for me

I do have to be very careful moving around inside the dome in the dark though, not much between my shoulders and the counterweights

Having no breeze to deal with makes it a little more comfortable too. I set it for 1hr worth of exposures, position the dome to give maximum travel across the opening and come inside, so far seems 1hr is as far as I can stretch it and I go out at the 45min mark just to be sure ...yes this will become annoying I guess buuuut baby steps...

Mike

[BC]

I notice a couple of people in this tread have mentioned a lack of dew with a foam dome. Would there be some benefit in lining an obs with foam? Geodesic triangles in an existing dome, of flat sheets in a ROR. Would any form of insulation assist (not sure if Mike's dome has this)?

Bruce