Nice little dew controller kit

[Rocket Pooch]

Hi,

I've read up about using a vellman 8004 kit as a dew heater controller, looks like it only needs a VR, box and cables to make it astro compatible, not bad for £10, probably £15 in total with all the bits.

Chris

http://www.rapidonline.com/productinfo.aspx?tier1=Educational+Products&tier2=Projects+%26+Robotics&tier3=Project+Kits&tier4=DC+to+pulse+width+modulator&moduleno=73984#

[Mike]

Yeah that would do the trick. You'd just need to add a box and the heating element.

[Ian]

not too dissimilar to one I put together for Tony a while back.

Did you have any success with it Tony? It might need some tweaking if not...

[Rocket Pooch]

I made one a while ago with an IC555 timer, it all works ok, but I'd like to do some more soldering so I'll give this a go, will give you an update.

I also made a dew strip for my 8" SCT yesterday, MK2 version much has insulation on the outside of the band and it feels a lot better than the MK1 version.

Chris

[RobertM]

Looks ideal, it's smaller and much cheaper than the maplin version too.

[The Thing]

Chris,

Did you use resistor ladders for your dew band of nichrome wire? I have always used nichrome but its a pain to insulate the 2.5m needed to get the right resistance.

Duncan

[Mike]

Duncan, you can get different thickness of nichrome which are obviously different resistances. Did you try shrink wrap tubing?

[The Thing]

I just haven't shopped around for different gauges, just got what Maplin had on the shelf (a while ago now).

Heatshrink is good but bulky. My last design was to create a dewshield 'liner' for my SKyWatcher 80mm which meant I could wind the nichrome around the plastic former I used and cover it with another layer of plastic. Welded the sheets together with a few soldering iron spot welds. Works nicely.

[Mike]

eBay is the best place for nichrome wire.

Heat shrink can be purchased in really small diameters too.

[Rocket Pooch]

Hi Dunc,

I use 330ohm 1/4 watt resisters in a ladder approx 20mm appart around the scope.  This really kicks off heat, on the MK2 version I have used double sided number plate foam on the back to act as insulation so less of the heat goes out side the tube, the dew heater is also positioned the heater behind the corrector and not on it, or in front of it, this way a) I use less heat and b) it causes less heat turbulance.  I shortened and put my mk1 strip on the ED80 and its allways clear with only a 15% power setting on the heater controller.

This is where I got the design from.

http://www.dewbuster.com

http://www.dewbuster.com/faq/3_heaters-sensors.htm

Chris

P.S. Tesco are selling 5mm thin black (with silver coating on one side) roll matts, these would make a nice dew sheild.

[RobertM]

P.S. Tesco are selling 5mm thin black (with silver coating on one side) roll matts, these would make a nice dew sheild.

I'm after a couple of dew shields.  Have you used one of these Tescos mats?

[MarkS]

I used a Maplin drill controller (http://www.maplin.co.uk/Module.aspx?ModuleNo=30310) but it cost 15 quid and only goes to 3A - works really well for dew strips and Peltiers.  Would definitely go for the Vellman next time.

For some time I used a silver coated roll mat on my C11 (silver side out).  Worked really well but eventually wanted something a bit blacker on the inside so I ended up buying a dedicated one.

[Rocket Pooch]

I'm after a couple of dew shields.  Have you used one of these Tescos mats?

No, but I would not put one on a C11 or something large but if its a refractor or camera lens then yes they would be good.

Chris

[Mike]

This is how you make nice flexible strips :-

http://www.myastrospace.com/DIY_Dew_Heater.htm

[RobertM]

That's what I did using solder braid but you have to be really quick making the joints.  The solder braid is rather too good at what it's designed for...