How hot should a dew heater get?

[earth titan]

Just a quick one.

I've just fitted my 1st dew heater tape to a scope (C9.25).

Although it shows some signs of getting warm, it isn't hot at all. So how warm should it get?

I haven't had a chance to test it yet in anger, but will this really clear dew?

[Tinker1947]

I believe it only needs to transfer heat to the selected item enough to warm it a couple of degrees above the air temperature, if you can insulate it so there no heat loss to the atmosphere...

[VigdisVZ]

If you can get it so fine tuned that you barely feel any heat at all, but it's enough to clear your optics, you've tuned it good. Remember, you only want a few degrees, more temp will screw up visuals and very much heat and you risk fractures (although a regular heater should be incapable of this if properly installed).

[earth titan]

Its a proper manufactured one. An Astrozap.

It gets barely warm which is what surprises me. I would have thought it would have needed to have got hotter to warm the OTA slightly.

Never having played with one though, I'm not sure what to expect.

[Moonshane]

I never use them but my understanding is that you use them on a 'just enough' setting. the idea is not to warm the optics but to keep dew at bay. t do this the optics should be close to but marginally 'warmer' than outside temps. if you are observing at -5c then the scope would not get warm.

[earth titan]

I never use them but my understanding is that you use them on a 'just enough' setting. the idea is not to warm the optics but to keep dew at bay. t do this the optics should be close to but marginally 'warmer' than outside temps. if you are observing at -5c then the scope would not get warm.

That is my understanding, but I'll know more if I ever get to try them

Love the avatar by the way. One of my favourite comedians!

[Luke]

My dew heater at full pelt gets warm-ish, nowhere near hot. When I have it a bit lower at a level that normally keeps the dew at bay it hardly feels warm when I take it off, but it's nowhere near as cold as the scope tube.

I was expecting the heater to be warmer but it does the job brilliantly.

[earth titan]

My dew heater at full pelt gets warm-ish, nowhere near hot. When I have it a bit lower at a level that normally keeps the dew at bay it hardly feels warm when I take it off, but it's nowhere near as cold as the scope tube.

I was expecting the heater to be warmer but it does the job brilliantly.

Having tried it last night, I would say mine hardly gets warm to the touch. That's comforting to hear.

[GlassWalker]

I got a couple of dew-not strips today, but I was too tight to pay for a controller They're quite low power anyway so I think they will be ok run on full power. The heat is spread over such a large area, it wouldn't be much I think. And rough calculations show if I drop it to 9V as opposed to 12V (which my powertank also does) that'll almost half the power.

[Islander]

My home made dew heaters can get quite warm to the touch and I've just been given one for the secondary of the LB16 I've just bought and that gets very hot on full power. I really must measure the current draw.

[billhinge]

I also use the astrozap dewshield and controller and it doesn't get hot but it definitely works. I only use 2 settings, off and full (maybe I should be more critical but it doesn't cause me problems so far)

Just checked the dew shield, it draws about 2A at constant 13.8v on my ac psu i.e. just over 27watts on full

[LukeSkywatcher]

I have an astrozap heater strip also and a Hitechastro controller. Even when i turn ther controller up to full, the strip is what you would call luke warm. Thats enough to heat the OTA and keep it a couple of degrees above the outside temp.

[Andymarrison]

I use the same Astrozap dew strip with my CPC800, and I was also surprised that I couldn't detect any warmth at all. It works, though! I also have a small Astrozap strip for my 2" EPs, and when I put my eye to the EP I can detect some warmth, which gives me some comfort that the strips are indeed doing something! Also, with the two strips on at once they ran down my 20Ah power pack very quickly, and I needed to upgrade to a leisure battery as a result!

[earth titan]

Well I can now report, the heater works. Takes time to clear the corrector from fully misted (10 minutes) and on 75% it keeps it clear for a night's viewing.

Just need to sort the eyepieces now..... oh and the guide scope and the imaging scope :-)

Does anyone know if I need both a 1.25" heater and a 2" for eyepieces? Or will the 2" do both?

Typed by me on my fone, using fumms... Excuse eny speling errurs.

[Andymarrison]

I've got both but I tend only to use the 2" - you can just wrap it in a spiral-type style so that it covers more of a 1.25" EP.

[Islander]

Another method is to make a heater for the diagonal itself or make one out of nichrome wire that wraps around the eyepiece receiver in the diagonal. Either way saves having to change the tape over every time you change an eyepiece

[earth titan]

I'm thinking a 2" heater may wraparound the diagonal with an extra bit of velcro. I'll try that and see if it works.

Typed by me on my fone, using fumms... Excuse eny speling errurs.