Heating the secondary on a 200mm Newt

[palebluedot]

I am in the process of dew proofing, as much as possible, my 200P using heaters I am having problems finding a solution for the secondary mirror. I am aware of the age old DIY camping mat dew shields and hair dryer solutions often suggested, but the dew shield only delays the onset of dew (for me at least) and the hairdryer in my opinion is not a good idea as well as being a pain in the rectum.

I had my mind set on the Kendrick split heater, but these are not made for secondaries with a diameter less than 71mm on the minor axis. So, I was thinking of heating the mirror by wrapping a small heater strap around the stalk, insulating and running on low power, has anyone tried this? I am quite aware of the air currents that can be caused by not insulating sufficiently, other than this, can anyone think of a reason why this might not be a good approach?

[cs1cjc]

I now run a fan on the primary continuously while observing. For me, the airflow has been enough to keep the secondary clear, so far at least.

[cotterless45]

I hear than a more elegant solution is to get a torch bulb (not led) , wrap it in silver foil and connect it up to an AA battery and fix the whole thing securely beneath the 2ndry. The heat from the bulb will be just enough to keep clear of dew.Neat,

Nick.

[Breakintheclouds]

There are various commercial secondary dew heaters out there, such as this one. Why not have a look at these and either buy one (the easy, lazy solution!) or base your design on what seems to have worked for these designers?

[Velvet]

I have seen a mod where a resistor has been attached and wired to the rear of secondary to provide heat for it. Maybe

this would help? It was on a 200p because they do not produce anything of the right size for a 200p secondary i dont think

velvet

[palebluedot]

I hear than a more elegant solution is to get a torch bulb (not led) , wrap it in silver foil and connect it up to an AA battery and fix the whole thing securely beneath the 2ndry. The heat from the bulb will be just enough to keep clear of dew.Neat,

Nick.

Liking it. But would like something a little more permanent.

[palebluedot]

There are various commercial secondary dew heaters out there, such as this one. Why not have a look at these and either buy one (the easy, lazy solution!) or base your design on what seems to have worked for these designers?

Thanks. That'll be the Kendrick split heater that I had my mind set on and my strap heater idea is a variation on their 'wrap-around secondary heater', both in my OP.

[palebluedot]

I now run a fan on the primary continuously while observing. For me, the airflow has been enough to keep the secondary clear, so far at least.

I assume the the fan is situated under the primary on the outside? How does that keep the secondary clear?

[dark knight]

I fitted out my wifes 12" dob with 2 resistors to the back of the secondary, the secondary acts like a large heatsink, it works a treat and is permanent, it has no effect on the scopes visual use, is fairly simple to do and can run off a 9v batterry if required, although we use a celestron power tank at 12v. If I get the chance I'll put some photos up later

[Damo636]

I have a simple dew shield made from camping mat foam, & a fan running continuously behind the primary. The combination of the two works well.

[palebluedot]

Velvet/Carl,

Interested in the resister concept. Carl, what tolerance resistors have you used? I have a mixture right up to 2.2 M Ohm.

Pictures would be appreciated.

[palebluedot]

I have a simple dew shield made from camping mat foam, & a fan running continuously behind the primary. The combination of the two works well.

Cheers Damo, but this thread is really about heating the secondary. Thanks anyway

[dark knight]

think the resistors either provided 1 Watt each or 1/2 Watt each, they are square and have a metal back on one side, this metal side is attached to the back of the secondary using heat sink sticky pads. On the lightbridge the secondary mirror holder is a plastic housing so I had to use a Dremell to cut small apertures for the resistors to gain access to the glass surface of the mirror. I'll do the photo's later today.

[dark knight]

In fact here's the thread I followed, it has all the info and parts you need. This works very well and have not found it detrimental in any way in the use of the telescope

http://stargazerslounge.com/topic/51656-diy-dew-heater-80-complete-and-working/

[palebluedot]

In fact here's the thread I followed, it has all the info and parts you need. This works very well and have not found it detrimental in any way in the use of the telescope

http://stargazerslou...te-and-working/

Nice... Muchas Gracias! I assume some insulation is required to direct the heat into the mirror and not out into the tube? I'm thinking maybe some thermal grease on the side in contact with the mirror, fixed into place with some neoprene on the outside to provide the insulation.

[lukebl]

Have you looked at these complete DIY kits: http://www.dewityourself.com/. Haven't tried them myself, but they look pretty good and very affordable.

[dark knight]

the power resistors were attached to the secondary with some really sticky special pads that are used to transfer the heat, they act just like thermal paste., not found any need to insulate them from the tube on their outer face. Not found any noticeable thermal currents inside the tube affecting it's use.

This was an easy and cheap mod to carry out, and best of all it works., BTW you can omit the LED if you want, it is only included to show power is getting to the power resistors and they are switched on.

[palebluedot]

Have you looked at these complete DIY kits: http://www.dewityourself.com/. Haven't tried them myself, but they look pretty good and very affordable.

dewityourself.com... that's funny! I'll take a look, thanks Luke.

Sent from my Nexus 7 using Tapatalk 2

[cs1cjc]

I assume the the fan is situated under the primary on the outside? How does that keep the secondary clear?

The fam is indeed under the primary. It means that there is a constant gentle breeze on the secondary. Further, for much of the evening in the UK the breeze will have been warmed (very slightly) by the cooling primary.