I’ve 3 dobs and dew can be a problem. With commercial products being a bit pricey and unavailable, I wanted to try my hand at making few heaters for the secondaries.
For the heat strap, I 3-d printed a replica of the mirror using PETG. This will also serve as something to insulate the back of the mirrors with. I used 0.25mm nichrome wire and calculated that I needed between 1.0 and 1.6m of wire for my 4” secondaries. I settled on 1.1m as a trial. This was encased in 0.6mm heatshrink and then hot glued to the printed backing. Nichrome doesn’t solder well so was connected to the copper cable using aluminium crimps (available from fishing stores as it’s used in trace making) which was then reinforced with more heatshrink.
For the controller, I used a cheap motor governor. Has the advantage of showing the % power, but the LED could possibly be too bright.
I aim to attach to my mirrors using thermally conductive double-sided tape. This is used for 3d printers to stick beds to heat plates.
How well does it work? Very well! At full power, the wire gets very warm, but not too hot to touch. 50% likely enough for normal use.
I still need to design and print a case for the controller, but at least it works!
There will be leftovers so there is scope
to make some eyepiece dew heaters as well.
How much? I paid around $60 total (AliExpress, but shop where you prefer), including postage and some Velcro strips to mount the controler to the telescopes…so $20 each for something that commercially costs around $180.
