Dew Control Build

[M106]

I got a little fog on my scope last night, having read lots on ways to prevent it i'm working on a dew control system, would love some feedback on the design and build...

So far i've wrapped Neoprene (4mm) around...

bottom of the scope (approx 400mm, including ~100mm hanging off the end)

Top of scope (approx 250mm, including ~100mm extending past the edge of the tube)

Double layer around the main body of the tube (approx 600mm width)

Is that the right way? (photo attached, excuse dodgy tablet low light pic lol)

 

Heater Build

48W PWM 12V heat cable system (and ~4~8W for secondary heater)

I've just ordered parts to build some heat cable, 2 long sections for the primary mirror and the body of the tube, and a seperate heater for the secondary mirror

Primary Mirror and Main Body, heater specs:

4m of cable, giving 5 turns around the tube; approx 24W each

Not 100% sure on the secondary mirror  and eye piece heaters yet, i want to see how flexible/heavy/bulky the diy heat cable is first; i may build the heater directly onto the mirror rather than making a cable and then wrapping it around

 

Heat cable will be Nichrome wire inside PVC tape, with foil tape on the top/outside, cable with be underneath the neoprene

Hows that sound? 

 

Some questions...

Mixing warm and cold tends to get air moving around, how much could this affect what i see?

How much do i need to raise the temp? I'm thinking perhaps 0.2-0.5C above air temp? Or should i be aiming for something else?

I've got about 20W extra that i can safley play with via mains power, will i need it?

 

Will post up pictures and build diary when the parts arrive, incase its useful to anyone  total build cost is £36 for the heater system including PWM and power supply), and ~£15-20 for the neoprene sheet i think, bought it ages ago

[andyboy1970]

1) What country do you live in?

2) With my 200p & 150p I have only ever used a camping mat dew shield extending approx 30cm beyond the secondary end of the tube.

3) By far the biggest dew preventer in a newt. IMHO is a 12v Fan behind the primary mirror.

I personally would steer clear of adding heat in a Newtonian as you are going to add thermals inside the tube.

Hope this helps, it is my experience of observing with Newtonians over the last 30 years and quite a few of them years were in Scotland.

[mikeyj1]

So most of the time a dewshield isn't necessary on a reflector/don due to  that the tube full length is effectively a dew shield in itself .  

A dew heater for the primary is good, and possibly the secondary.  This is what mine looked like, (although frozen on outside)

I am also just about to build a nichrome dew heater and pwm drive, let's keep in touch ? Some reasonable designs out there although not much on YouTube.  Anyone got any good links?

Mike

[daz]

You might be better introducing a small fan at the base of the tube to give a gentle airflow, rather than introducing heat into the primary mirror. My blue-tube Explorer came with a metal plate that covered the base of the mirror and collimation screws - I removed it and fixed two small battery powered fans to it as far over to the edges as I could, and then drilled some some small holes to allow the air to flow. 

 

[M106]

48 minutes ago, mikeyj1 said:

So most of the time a dewshield isn't necessary on a reflector/don due to  that the tube full length is effectively a dew shield in itself .  

A dew heater for the primary is good, and possibly the secondary.  This is what mine looked like, (although frozen on outside)

I am also just about to build a nichrome dew heater and pwm drive, let's keep in touch ? Some reasonable designs out there although not much on YouTube.  Anyone got any good links?

Mike

 

thats what i had read before, that newtonians were already shielded in their design, but after ~80mins last night, i was reduce to a foggy blur :-/

 

This is the tutorial i found, the heat cable design is essentially the same as ones i've built before for other purposes; i'll post up a build diary and schematics once all the bits arrive, shouldnt be more than a week

http://www.deepskywatch.com/Articles/newtonian-dew-heater.html

 

 

52 minutes ago, andyboy1970 said:

1) What country do you live in?

2) With my 200p & 150p I have only ever used a camping mat dew shield extending approx 30cm beyond the secondary end of the tube.

3) By far the biggest dew preventer in a newt. IMHO is a 12v Fan behind the primary mirror.

I personally would steer clear of adding heat in a Newtonian as you are going to add thermals inside the tube.

Hope this helps, it is my experience of observing with Newtonians over the last 30 years and quite a few of them years were in Scotland.

Great info thanks! I want to avoid a fan if i can, the noise would drive me nuts, the quiet on a dark hill at 1am is a big part of the reason i love the hobby, probably second only to the view of space ...i live in london, directly under the flight path for heathrow, the noise is relentless lol

Taking on board what you said about thermals, it is something i thought about, for now i'll see how the shield works, and then i'll try just heating to air temp, rather than above (as i undestand it, the issue is with the scope cooling faster than the air)

[M106]

7 minutes ago, daz said:

You might be better introducing a small fan at the base of the tube to give a gentle airflow, rather than introducing heat into the primary mirror. My blue-tube Explorer came with a metal plate that covered the base of the mirror and collimation screws - I removed it and fixed two small battery powered fans to it as far over to the edges as I could, and then drilled some some small holes to allow the air to flow. 

 

I'm going to keep a fan as a last resort, i want as much silence as possible when i'm not dealing with planes every 90 seconds, buses every 60 seconds and endless car traffic & computers *bangs head on wall* lol

[andyboy1970]

I know Heathrow well, I worked there for 6 years in the 90's, I moved to Watford to escape the 24 hour noise.......

The computer type fans available from Maplins are virtually silent.

[M106]

3 hours ago, andyboy1970 said:

I know Heathrow well, I worked there for 6 years in the 90's, I moved to Watford to escape the 24 hour noise.......

The computer type fans available from Maplins are virtually silent.

"virtually" being the operative word.

Unfortunetly i have the hearing of a 14 year old, i work in music production, and i can almost hear a pin drop on the moon! (or would if there was an atmosphere to transmit the sound  )

[andyboy1970]

2 hours ago, M106 said:

"virtually" being the operative word.

Unfortunetly i have the hearing of a 14 year old, i work in music production, and i can almost hear a pin drop on the moon! (or would if there was an atmosphere to transmit the sound  )

Working as an Aircraft engineer for the last 26 years my hearing is shot!!!!

What about listening to music on headphones while observing, now that's a great way to observe.

[M106]

3 hours ago, andyboy1970 said:

Working as an Aircraft engineer for the last 26 years my hearing is shot!!!!

What about listening to music on headphones while observing, now that's a great way to observe.

so its Your fault i have these damned planes waking me up at 5am

I very rarely use headphones any more, i have several friends who have the hearing of 80 year olds because of them, eep! I do love the silence though anyway

[M106]

neoprene slowed down the fogging, but didnt stop it

ive made a very simple heat tape as a prototype, 4 parrallel runs of nichrome 32awg, 80cm long, @ 12V  more than enough power to give me lots of control with PWM, will give it a test run before building the final version, will take pics and post up a howto when its tested and working

i *think* it was the primary which fogged, so ive made the heat tape for that initially

[iapa]

On 11/01/2017 at 12:39, andyboy1970 said:

Working as an Aircraft engineer for the last 26 years my hearing is shot!!!!

What about listening to music on headphones while observing, now that's a great way to observe.

dare I suggest the Pentateuch of the Cosmology ?

I just used a dew heater around the primary end of my 200p-DS which worked fine to to -10C or so.