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Thread: Dew Heater

  1. #1
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    Default Dew Heater



    I'm making a dew heater out of 20 AWG Nichrome wire using 12vdc. The wire will be encased in 1/16" polyolefin shrink tubing that will be stuck (in an "S" pattern) onto duct tape. This will go around the outside of my OTA right where the corrector plate is. At the optimal length, 60", it gets hot, at the minimum length, 38", it gets really hot.

    My question is how hot in degrees F does the wire need to get to be an effective dew heater?

    If you have a Kendrick, or an AstroZap, or a homemade dew heater how hot do they get? Are they too hot to touch?

    I know I can vary the temp by either changing the voltage or changing the length of the wire, but I'm hoping the 60" length will be hot enough based on the input I receive here. My internet searches have given vague answers, at best, at how warm/hot the wire need to get.

    Clear, dew free skies,
    JT
    Main: C-stron CPC1100 #2 Scope: 8" f/7.5 Dob mounted Newt AP Scopes: TPO 6" RC f/9 & ES 80mm f/6 APO G&G Scope: Meade 102mm f/7.8 goto Guide Scopes: 70 & 80mm fracs Mounts: C-stron AVX CGEM & GT Alt-Az, Cameras: Canon T3i 2, ASI120MC Binos: 10X502,10.5X70,15X702, 25X100 EPs: ES: 21 100°, 30 82° X-Cels: 9,12,18,25 Clubs: RCA & HAS
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    Default Re: Dew Heater

    The heater I made needed some tweaking after making it according to the math. I had originally planned for something around four or five watts based on the S&T article Everybody's Do-It-Yourself Dew Heater - Do It Yourself - SkyandTelescope.com. It wasn't hot enough. I think you will have to do some R&D as there are variables that you won't be able to factor in. Mine gets hot but not too hot to touch. I bought a cheap PWM dimmer off Ebay to control mine.

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    Default Re: Dew Heater

    I use the little dimmer to control mine as well. You want to be able to go from "barely warm" to "moderately warm", but unless you are viewing in the Arctic, I doubt "hot" will be necessary for you. Anything over the dew point is going to delay or prevent dew formation. Anything over freezing will delay or prevent frost. Of course, the specific temperature depends on your weather conditions, so some variability built into the setup is nice.
    ~~Aaron
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    Observatory. I'd call it something nicer, but wouldn't want to misinform.


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    Default

    I have homemade dewheaters made with resistors and they get warm to the touch. At max power (straight from battery) they get to be 'hot', but I run mine with a dewbuster controller and thermocouple so I can preset how many degrees warmer I want the scope to be than the air temperature. I would guess with most of these heaters you don't want to directly run a constant 12V source to them but want use some kind of controller to adjust output. Hopefully someone with nichrome ones can chime in.

  5. #5
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    Default Re: Dew Heater

    Thanks you guys for the input.

    I just bought a PWM dimmer on ebay. Since I know that 12vdc at 60" is more than hot enough, I'll proceed with the heat shrink tubing and inlaying into the duct tape strip. If somebody has a heater strip for a C11 or close to 38-40" in length, could you tell me what the max wattage is for that strip? That info will help me approximate the temp. Thanks again.

    CS,
    JT
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    Default

    I think that will work fine. I suggest testing output before taping it up though. Consider putting some fabric inside tape on non-scope side of wire to help insulate it (prevent heat loss to atmosphere).

  7. #7
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    Default Re: Dew Heater

    The full plan is the nichrome wire is going into 1/16" polyolefin heat shrink tubing, that tubing will be inlayed in an "S" fashion between two sheets of duct tape. This "duct tape heater belt" will go directly on the metal of my OTA right above my corrector plate, then my flexible dew shield will go over the "heater belt" to insulate and hold everything in place.

    Thanks again,
    JT
    Main: C-stron CPC1100 #2 Scope: 8" f/7.5 Dob mounted Newt AP Scopes: TPO 6" RC f/9 & ES 80mm f/6 APO G&G Scope: Meade 102mm f/7.8 goto Guide Scopes: 70 & 80mm fracs Mounts: C-stron AVX CGEM & GT Alt-Az, Cameras: Canon T3i 2, ASI120MC Binos: 10X502,10.5X70,15X702, 25X100 EPs: ES: 21 100°, 30 82° X-Cels: 9,12,18,25 Clubs: RCA & HAS
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    Default Re: Dew Heater

    UPDATE!!!

    The design and build is posted on this thread.

    When is a dew heater required?

    Clear skies,
    JT
    Main: C-stron CPC1100 #2 Scope: 8" f/7.5 Dob mounted Newt AP Scopes: TPO 6" RC f/9 & ES 80mm f/6 APO G&G Scope: Meade 102mm f/7.8 goto Guide Scopes: 70 & 80mm fracs Mounts: C-stron AVX CGEM & GT Alt-Az, Cameras: Canon T3i 2, ASI120MC Binos: 10X502,10.5X70,15X702, 25X100 EPs: ES: 21 100°, 30 82° X-Cels: 9,12,18,25 Clubs: RCA & HAS
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