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  #1  
Old 25-05-2008, 09:41 PM
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browndog (Ian)
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Dew heater advice?

I would like some opinions on what dew heater I should get for my C8 SCT?

I currently have a dew shield, but I am finding that I am getting dew forming. So understand that my only alternative is a dew heater.

Do I make a DIY? or do I purchase??
Which is best?
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  #2  
Old 25-05-2008, 09:55 PM
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mick pinner
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l use a Digifire 7 with Kendrick straps on my SCT and refractors and have no dew problems at all. not the cheapest system around but does a great job.
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Old 25-05-2008, 10:08 PM
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acropolite (Phil)
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I did a DIY controller, and bought a strap from Scopestuff in the US for $35.00. Total cost around $50 for the lot. Since I made the controller, I haven't had a single night where I've had to use it.

You can also roll your own either with resistors or Nichrome wire. This site has a circuit diagram and details on how to make a heater with nichrome wire and silicone tubing. Some of the other guys have used an off the shelf kit from DSE or Jaycar, you should be able to get details by doing a search of the forum.
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  #4  
Old 25-05-2008, 11:45 PM
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JethroB76 (Jeff)
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Dew Not are an option if you decide to purchase either heater straps or the controller itself, can be bought in from the US or I think SDM scopes sell them in Oz
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  #5  
Old 26-05-2008, 08:26 AM
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sheeny (Al)
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I use a commercial (i.e. purchased) dew heater strap for my C8. I can't remember what brand, but I know it isn't a Kendrick... doesn't matter much which brand... My feeling is a strap is probably better than resistors for a large aperture like the scope, but for smaller apertures like your finderscope, EPs and camera lenses a DIY project with resistors is quite feasible in the long term. My main concern is handling over a long period of time and maintaining reliability.

If you want to build your own, have a look here:

http://www.iceinspace.com.au/index.p...63,292,0,0,1,0

and

http://www.iceinspace.com.au/index.p...63,285,0,0,1,0

Al.
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  #6  
Old 26-05-2008, 09:09 AM
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Omaroo (Chris Malikoff)
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Ian - here are a couple I've made for my 12" and 8" SCT's and all of my refractors. I made both of these straps as well as the pulse-width modulated heater controller described here:

http://www.backyard-astro.com/equipm...dewheater.html

The number and type of resistors is determined for each application by a fantastic spreadsheet provided by the above poster - Al Sheehan. It's worth its weight in dew. I usually use 390 ohm, 1/2 watt jobbies.

For the straps themselves, I used the resistor method because quite frankly nichrome wire sucks. It's hard to work with and connect in a circuit (won't solder) and breaks without warning. Being a series circuit, one break and Nichrome's gone. The difference with my resistor-based heather strap system to most is that I lay the resistors down in parallel across two lengths of flexible copper braid - or solder wick. Soldered quickly, the joints remain small and wet, without solder spreading too far along the braid so that flexibility is maintained. This strip assembly is then laid down on a strip of flexible plastic about 12mm wide and all of it is then encased in a tube of heat shrink tubing.

I also sometimes leave out the plastic strip and encase just the resistor assembly in heat shrink so that it remains very flexible - so that it can be used wrapped around eyepieces (with velcro) as well as being used in places such as my red-dot finder optics.

Making these are fun - and effective. I've never-ever had a dew problem. Power usage is minimal - and even my 56-resistor 12" SCT strap only draws about 0.75 (measured) amps when in use at full bore. Their positioning - inside the flange, rather than outside the tube, makes them far more efficient and I use a fair amount less power than some of the professionally made units. You want to heat the AIR at the corrector plate interface - not the corrector plate or telescope. This way, you effectively achieve the same thing - keeping that air's temperature a couple of degrees above ambient, without having to heat the hardware itself - which is just a big heatsink.
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Last edited by Omaroo; 02-06-2008 at 10:31 AM.
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  #7  
Old 26-05-2008, 11:46 AM
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Omaroo (Chris Malikoff)
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Ian - as per my email back to you - here's my current 2-port heater controller. I've never found that you need a multi-port controller that allows individual settings - unnecessary expense in my book.
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  #8  
Old 26-05-2008, 07:30 PM
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Another question is ....


how many do you need for a 1000mm long scope.
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  #9  
Old 26-05-2008, 10:37 PM
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Omaroo (Chris Malikoff)
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Quote:
Originally Posted by westsiderailway View Post
Another question is ....


how many do you need for a 1000mm long scope.
For me - zero - I've only ever used a dew shield and a fan on my 8 inch Newtonian. A secondary heater for a newtonian is a bit of a specialised affair.

Last edited by Omaroo; 27-05-2008 at 11:00 AM.
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Old 27-05-2008, 10:21 AM
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PCH (Paul)
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Guys,

At risk of posing a bit of a daft question, - what powers these dew heaters ?

Cheers,
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  #11  
Old 27-05-2008, 10:57 AM
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Hey there Paul

Because I run 9 individual heaters on my imaging rig - power needs are quite high. For this reason I use my 80AH (amp-hour) 12vdc deep cycle battery that I've encased in a box and added all manner of different plugs to - from a large Anderson plug to ciggy, Merit and microphone plugs for the various uses I have for it. This large battery also lets me power the G11 mount and two laptops off it all at the same time.

If your needs are less, then you can get away with a 12v "motorcycle"-style battery such as the one I've shown. These are typically rated at 17AH and will give most people a night or two of heating - depending on he efficiency of their heaters.
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Last edited by Omaroo; 27-05-2008 at 12:10 PM.
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  #12  
Old 27-05-2008, 07:58 PM
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PCH (Paul)
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Hi Chris,

thanks for that All perfectly clear now.

Cheers,
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  #13  
Old 28-05-2008, 05:57 AM
westsiderailway
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Quote:
Originally Posted by Omaroo View Post
For me - zero - I've only ever used a dew shield and a fan on my 8 inch Newtonian. A secondary heater for a newtonian is a bit of a specialised affair.

So what are the two heaters that you use.?
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  #14  
Old 28-05-2008, 07:13 AM
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Omaroo (Chris Malikoff)
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Quote:
Originally Posted by westsiderailway View Post
So what are the two heaters that you use.?
I have two output plugs, but only ever really use one. I then use in-line 12v plugs once the main lead reaches the OTAs and there I have double and triple-adapters branching off to everything. The main reason I do this is so that the cabling following the flexible line of the equatorial head is kept to an absolute minimum to avoid its bulk upsetting the balance and natural movement of the head.
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Old 28-05-2008, 07:07 PM
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Quote:
Originally Posted by Omaroo View Post
I have two output plugs, but only ever really use one. I then use in-line 12v plugs once the main lead reaches the OTAs and there I have double and triple-adapters branching off to everything. The main reason I do this is so that the cabling following the flexible line of the equatorial head is kept to an absolute minimum to avoid its bulk upsetting the balance and natural movement of the head.

A nice ramberling reply, but did not answer the question asked.
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  #16  
Old 28-05-2008, 07:23 PM
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Omaroo (Chris Malikoff)
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Quote:
Originally Posted by westsiderailway View Post
A nice ramberling reply, but did not answer the question asked.
Not sure I deserve the emoticons you've used, but oh well...

Your question was "what two heaters do I use". I stated that I use nine heaters and I was under the assumption that you were asking about the two plugs at the end of my heater controller.

Otherwise, where did you get "two" from - or are you referring to my use of the word "secondary"? I was referring to the secondary mirror in your Newtonian scope (assuming that your signature gives me that information correctly) - not a second heater. I don't use heaters on my Newtonian - just the fan in the base behind the primary mirror cell. The draft from the fan works its way up the tube and keeps the secondary from dewing up as long as you have a dew shield on and your tube is covered (i.e. not an open truss design).
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Old 31-05-2008, 02:08 PM
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Quote:
Originally Posted by Omaroo View Post
Not sure I deserve the emoticons you've used, but oh well...

Your question was "what two heaters do I use". I stated that I use nine heaters and I was under the assumption that you were asking about the two plugs at the end of my heater controller.

Otherwise, where did you get "two" from - or are you referring to my use of the word "secondary"? I was referring to the secondary mirror in your Newtonian scope (assuming that your signature gives me that information correctly) - not a second heater. I don't use heaters on my Newtonian - just the fan in the base behind the primary mirror cell. The draft from the fan works its way up the tube and keeps the secondary from dewing up as long as you have a dew shield on and your tube is covered (i.e. not an open truss design).

Now that was the answer i was looking for...

Is your focal length shorter because of the fan inside the tube.?
What sort of fan is it,,,ie specialy made /custom job or one of the rack.
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  #18  
Old 31-05-2008, 07:56 PM
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peter_4059 (Peter)
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Chris,

Thanks for sharing your heater strap design - made one for the ED80 today - works a treat. Now for the finder and Telrad! Also picked up a 3A PWM controller from RSaustralia - $30 assembled.

Peter
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  #19  
Old 02-06-2008, 10:21 AM
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browndog (Ian)
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Thank you for your advice Chris .
I made a dew heater strap using your design and the spread sheet created by Al Sheehan. (It was all reasonably easy - I think that I surprised myself at how simple it all was.)

I tested it last night and the C8 was dew free all night . Yippy

The only problem was the guide scope damn... I didn't make a dew heater strap for the guidescope and it was covered with dew. So I have another project this week.
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  #20  
Old 02-06-2008, 10:30 AM
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Omaroo (Chris Malikoff)
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Excellent Peter & Ian

Any photies of your new masterpieces?
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