Dew Control

[jjjnettie]

I was sorting through boxes of stuff the other day and came across a heating belt designed for home brew carboys.
Any reason why I can't wrap it around the bottom of my scope to keep the mirror on my 8" warm and cosy?

[Mike21]

Could this be a cheap alternative Jeanette?

[Davros]

Does it have some form of temperature regulation. If so i cant see why not. As long as you keep an eye on it.

[jjjnettie]

There's no temp regulator, but it's intended to keep the brew at a constant temp of around 18 degrees.
It cost about $40 and that's heaps cheaper than a purpose made one isn't it.
There are also heat pads for $50 that could be useful for refractors.

[erick]

Is it 240V Jeanette? Is it marked with a wattage spec?

[erick]

ps. why are you trying to keep your primary mirror warm when most are trying to get them cold! Have you had it dew up?

[jjjnettie]

Yep, I've been dewed up a couple of times recently.

[jjjnettie]

I've been poking the hairdryer between the vanes to dry it.
Oh so carefully. You don't want to be recollimating halfway through an imaging session.

[jjjnettie]

Mine's either 25 or 30 watts.

[coldspace]

It might get a little warm for the mirror unless you don't have too much direct contact.

You really only want to bring the temperature up just past the dew point or at ambient.
I use these heaters in my home brew as well and they can warm your 25ltr brew about 10 to 15 degrees above ambient but this takes time to do.

These will work, you will just have to play with the amount of direct contact with the back of your mirror to keep it dew free without too much heat.
Try it out.

Regards Matt

[erick]

That's a lot of watts. When I tested heater straps, an 8" dia strap was consuming a maximum of 12V x 1.1A = 13W running flat out. In normal operation on an SCT corrector plate, it is probably consuming more like 3-5 watts.

Keep an eye on it.

[sheeny]

Its not going to be a safety risk if dew runs down the tube onto it, is it?

If not, I would suspect the biggest problem may be it's too warm and may cause thermal currents in your OTA which will give you mushy shots...

:shrug:

A dew heater ona newt mirror seems to be contrary to my understanding of what most imagers with newts are trying to do. What you need is a little hatch in the side of your tube that you can use the hair dryer through when needed.;) I'm pretty sure Mike did that mod on one of his scopes...

Al.

[jjjnettie]

I guess one would only use it for short periods during the night, not leave it on all the time.

[jjjnettie]

Al, I know what you mean.:lol: It's a bit of a contradiction isn't it.
I leave my scope out to cool for hours, then I want to apply heat to the darn thing.
But it's frustrating to have to stop and defog time and again during the night.

[astronut]

Jeanette,
Does your scope have a fan?

[CoombellKid]

I occasionly have the same prob with my 16". Usually late around 3-4am
if the scope has been out without it's rain coat, well prior to having a
raincoat made anyways.

You maynot have to use a dew heater of sorts. A gentle breeze should
be enough. Perhaps if you mod the scope by installing a couple of fans
on the OTA, locate them just above the level of the front surface of the
primary and have them suck air off the top of the mirror surface and
blow it out the side of the OTA. This should dry off the dew deposits
and maybe better than trying to heat up the mirror.

You wouldn't need to have it going continually just between imaging
runs.

Cheers,CS

[jjjnettie]

ahhh,
No Fan.

See, I had no probs with my 10" cause it had a fan.

[TrevorW]

refer

http://www.abc.net.au/news/stories/2009/08/12/2653111.htm?section=world

[astronut]

Jeanette,
I have a fan on my 12"LB. It stays on all night.
I have never lost an observing session "due to dew".on the primary.:lol:
Once the fan is switched off (especially on a very wet night) the mirror fogs up very quickly.
So........just a simple computer fan will be enough, and they consume very little power.:thumbsup:

[Davros]

I've found dew on the secondary of my 10 inch. It has a fan but it has only dewed the secondary up after many hours at around 2 or 3 am. Since i made a dew shield (camping bed foam extension tube) i have had no dew problems.