Condensation

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  • #573645
    Nick Atkinson
    Participant

    I have a pusar dome and with the cooler and moist laden air suffer condensation on the roof but the walls and floors remain largly free from this. There are 2 ways of improving this ; either by the use of a small heater to raise the dew point or the installation of a de-humidifier. I will be interested to hear from members the solution they have adopted and the equipment they use

    #577705
    Andy Wilson
    Keymaster

    Hi Nick,

    I have an 55W electric tube heater which I leave on in my observatory. I also have a cold air dehumidifier which I run for a couple of hours after I’ve closed up my observatory. I find things due up during an observing session, and this takes away the moisture. This is particularly important for me as I leave a desktop computer in my observatory.

    Andy

    #577708
    Jeremy Shears
    Participant

    Hello Nick,

    I have a Pulsar observatory too, as you can see in the photo on the left! I also get some condensation on the inside of the dome, but only really when I am out there using it. I haven’t done anything about it as it has usually gone by the next day. No detrimental effects after 12 years. I have thought about a dehumidifier, like Andy uses, but I fear the electricity bill – there is quite a large airflow through/around the dome.

    All the best,

    Jeremy

    #577710
    Steve Cuthbert
    Participant

    +1 for the Pulsar dome. Never had a problem with damp but my laptop is never left in the dome and my NEQ6 seems happy enough sat there. I do keep my ccd`s covered when not in use though.

    Steve

    #577711
    Eric Watkins
    Participant

    Hi Nik,

    I have a 2.7m Pulsar dome, that sits   on top of a wooden building.

    I found I got heavy dew on the dome and more worryingly, surface water on the metal work of the paramount gem. I also keep a desktop in  a large plastic box.  I keep the PC powered on and have installed a small DE-humidifier that runs  24/7 during the damp season.

    I have had no problems during the past four years. 

    Eric

    #577712
    Jeremy Shears
    Participant

    Hello Nick,

    thinking about this again, I do remember a bit more condensation in the first year after installation of the observatory. I suspected that some moisture was coming out of the concrete base upon which the dome sits. I gave it several coats of concrete sealant paint which stopped that – I put another layer down every couple of years, just to be sure (and to give it a nice aesthetic finish!). I also made sure the join between the bottom fibreglass flange and the concrete base is properly sealed with exterior grade door sealant. I renew this periodically, again just to be sure.

    All the best,

    Jeremy

    #577713
    Bill Leatherbarrow
    Participant

    Hi Nick,

    I have had a Pulsar dome for over three years, and it does the job well. There are no problems with leaks or other significant water ingress, but there is the occasional thin film of condensation on cold metal surfaces. Not really a problem, but I address it with an ELA DD822 Dehumidifier and Laundry Drier bought from Dry-it-Out.com.

    http://www.dry-it-out.com/DD822-Graphite-dehumidifier

    Running costs are not really a problem – it only needs a quick blast once-or-twice a week. I find it an ideal solution and everything is kept bone dry.

    Very best,

    Bill

    #577717
    Andy Wilson
    Keymaster

    I did once have condensation forming on my CCD coverslip. This can happen with some CCDs when they are kept in a damp environment.

    I now place a silicon desiccant bag in my telescope tube when I’m not using it, which I replace and reactivate every so often. I’ve not had any problems since doing this.

    Andy

    #577947
    Vic Hull
    Participant

    The local water table is just below the lawn surface where I live (in a dip with a stream) so moist air is a problem all year round.  Since I have a roll-off obs. when the roof shuts the local air is trapped and moisture always settles on the OTA & mount – never the wooden walls or roof. I quickly acquired a de-humidifier and run it on a timer for 3 hours during PM, from mid-Oct to mid Mar.  This allows the air inside to warm up, even on cloudy days, and maximises the efficiency of the de-humidifier.  Everything stays bone-dry!  If I don’t (and I’ve experimented) then mould & rust quickly becomes a problem.

    #577948
    Robin Leadbeater
    Participant

    You should try keeping a flip top dry!  The moisture condenses on the inside of the open roof and can even rain down on the gear when you close it up.  I run a dehumidifier 24/7 (with a tubular heater when it is below freezing), though apart from after I close up, it never seems to be running when I go back to it. The observatory volume is very small though!

    http://www.threehillsobservatory.co.uk/astro/observatory/observatory_C11_LHIRES_feb_2010.jpg

    #577949
    Tony Angel
    Participant

    I have a Pulsar Dome. It is lined with ceiling tiles on the inside. No condensation. Around the outside bottom edge there is a six inch curtain made of roof liner. This reduces the amount of low cloud getting in.

    #577952
    Peter Carson
    Participant

    I have a fibreglass dome and walls containing my 315mm reflector on a Paramount. I’ve got a built in damp proof membrane in the floor and the building is completely watertight. However my dome is not draught proof enough to dehumidify the building, I would be dehumidifying the whole world, so I cover the telescope and mount with a cotton sheet and use two 60 watt tubular heaters to warm the air space and raise the dew point. That works most of the time but occasionally when the ambient temperature warms rapidly I do get condensation on the Paramount and sometimes the telescope mirror, so I should really try to cure that. I leave my PC out in the observatory and have only had one failure in about 10 years.

    #579183
    Lars Lindhard
    Participant

    My old roll-off observatory is a bit worn and it might be time to replace it with something else.  A Pulsar dome seems to be a possibility – although rather expensive – but I fear that moisture might be a problem, as I can read that some of you have to deal with moisture in your domes.

    I don’t want to place my telescope inside a wet “tin can”.

    Pulsar has made this gadget

    https://www.bresser.de/en/Astronomy/Domes/PULSAR-Ventilation-System-for-Observatorium.html

    Do you think that this could help?

    Regards
    Lars

    #579184
    Peter Carson
    Participant

    Hi Lars,

    The forced ventilation kit will help move the air around and reduce condensation in humid weather. It will also help flush out warm air after hot days so your telescope will reach night time temperatures more quickly.

    However I find I get the most condesation problems when the mount and telescope have been cold for a long period, say after a prolonged period of cold weather, then the weather suddenly warms up. The warmer air carries more miosture and this condenses on the cold metal surfaces and even the optical surfaces. Additional ventilation at this point only makes things worse by supplying more moisture laden air to condense on the cold surfaces. Heat or dehumidification is the only way to resolve this situation. I said in an earlier post that I previously used small tubular heaters to reduce the condensation issues but have recently reverted to dehumidification which works perfectly and for a cost lower that the ventilation kit in your link.

    Peter Carson

    #579189
    Nick James
    Participant

    If I remember correctly Gary Poyner had a heater like that in his telescope and came out one day to find that it had caught fire and melted his telescope tube. I’m sure it worked well at stopping condensation though…

    #579190
    Gary Poyner
    Participant

    Always a pleasure to be reminded of that incident Nick.  Many thanks.  Another round of counselling coming up! 🙁

    I now have two – 60w and 120w – thermal tubes located at the mirror end of the 51cm.  They take it in turns to keep the primary cosy, and it seems to work OK.  The one that caught fire 18 years ago was kept inside the (horizontal) tube of a 40cm.  It worked like a dream for many years – until it didn’t.

    I do get some condensation from the plastic roof of the observatory, but I don’t worry about it.  Just cover the scope with a tarp!  I’ve been using the same ‘hinged roof’ observatory/shed for 31 years now, and it’s never been an issue.  My previous observatory was of the same design which I used for over 10 years and I didn’t worry about condensation in that either!

    Gary

    #579191
    Grant Privett
    Participant

    You have a dew zapper. Do you ever get ice or dew on the corrector plate of the C11?

    #579192
    Robin Leadbeater
    Participant

    Hi Grant. 

    I also run with a home made dew shield unless it is too windy. This keeps things clear all night except once when the dew shield fell off ! 

    Robin

    #580429
    Nick Atkinson
    Participant

    Hi, many thanks for all your replies. My wife came up with the idea to prevent water ingress under the base was to use pond seal, designed to repair concrete ponds aplied to the concrete base provides a fine surface for application of a flexible sealant. Having belatedly replaced my old wooden frames with double glazing the glazier suggested using roofing bitumatic as this will apparently stick everything despite being rather messy.

    Clear skies

    Nick

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