I made the cover from the interesting red material Rhonda gave me and with one of her (repaired) sewing machines.
Flipped the cover right-side out. That went easier than I thought, thanks to a pencil. The white twist tie, by the way, is in place as a means of securing the strap to eyepiece or camera lens, an alternate means than an elastic band.
I remembered at the last second to install some foil, shiny side inward, to redirect some of the heat energy toward the ocular or lens.
I made it the cover a tad small and found it quite tight but after a couple of goes, and clearing a snag, I got the sheath over the entire assembly.
Done! Woo hoo! Well, all but done. The very last thing I need to do is sew up the opening, by hand. As I do that, I'll pick up the wire jacket, so to secure and stabilise the whole strap.
Really happy with the way this looks and feels.
3 comments:
Thank you for your informative posts and video on building a dew heater. I have started to work on this project for my 12-inch Dobs, which I have wanted to do for years. A few questions: 1) You used the foil strip to reflect heat back to the inside of the heater band. What about a strip of foam insulation behind it to reduce heat escaping to the outside of the band? 2) Did you base your calculations for required power with a target of 0.3 watt/cm (or some other value) or did you start with a particular length of wire and base the required current and resistance from there? 3) Have you had any problems with breakage of the nichrome wire due to wear at the notches where it is mounted to the plastic strip? 4) If the calculated length of wire seems longer than should be necessary due to a high calculated resistance and low current, can you increase (say double) the current and reduce the resistance to shorten the calculated wire length without ill effects? Thank you for any help with these questions.
hi WU...
Q: What about a strip of foam insulation behind it to reduce heat escaping to the outside of the band?
A: Sure. I supposed anything with good insulating characteristics would work. I used foil thinking it would be good at reflecting the infrared energy. My objective was to get as much heat going in, not out.
Q: (Paraphrased) On what did you base your calculations for required power.
A: I started with a target wattage. And that came from examining what other similarly sized heaters or straps were producing. That then determine the resistance value. I had the length of wire required based on the design. So then I knew the target ohms/metre. I selected the resistive wire to match this target value, as closely as possible.
Q: Any problems with breakage of the nichrome wire due to wear at the notches?
A: No. And I'm not anticipating any. Where I have trouble is at the junction ends! I need better strain relief where the power lead wire connects to the heater strap.
Q: If [the wire is] longer than necessary due to a high calculated resistance and low current, can you increase the current and reduce the resistance to shorten the calculated wire length without ill effects?
A: I think you want to consider the maximum wattage that will be produced. You don't want to set anything on fire! You also want to ensure there's sufficient power output for heavy dew or frost. I bench-tested things before assembly.
Good luck with your project!
Also, WU, have you seen this?
https://www.youtube.com/watch?v=frE3ETTkBys
Might give you more info...
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