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Dew heater for working temp minus 10 to minus 20 degrees celcius.


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Winter is coming and I struggled the past days with dew on my Skywatcher 120ED. I have tried to use a self made isolation dew-cap around it, but not good enough (still dew)

I have browsed trough the forum and read about dew heaters vs. Dew shield, and figured out that I probably need a dew heater. The temperature here can range from minus 5 to minus 35 degrees celcius, but I dont think I’ll be using the scope when passing minus 20.

My question is, which dew heating option would handle minus 10 to minus 20 degrees celcius for my scope? I am afraid that the temperature loss will make the strips not functioning well when passing minus 10 degrees, but I might be wrong?


I guess my scooe is around 45cm circumference outside the tube.

I am using 220V with adapters to everything else, so power is not an issue. 

Edited by MHaneferd
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  • MHaneferd changed the title to Dew heater for working temp minus 10 to minus 20 degrees celcius.

I'm guessing it does not really matter which one you use. As long as it keeps the scope slightly warmer than ambient it should still prevent dew. I do not think the actual temperature is that important. I have used both 12v and USB powered heaters and both work well. For 45cm you probably need 12v.

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I have used mine down to about minus 10 without issue. If it is very cold I turn the power right up. I can't say about minus 20 as it is not normally that cold here! Even the USB heaters put out a fair bit of heat. The other option is to make your own then you can choose the wattage you want. I have made dew heaters from nichrome wire and resistors - both work well. Nichrome is a bit fiddly to work with, but if you are handy with a soldering iron it's not too bad.

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15 hours ago, MHaneferd said:

Thanks again. I’ll buy two strips to be at safer side and just see. Hopefully it manage the winter here..

For me here, last winter was easier in terms of dew than current conditions. Relative humidity of 99% in -20 is still less water in the air than a humidity of 50% at +10. It will work out great.

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