finder scope heater done

Built a heater for my Celestron 6x30 finder scope!

I used nichrome wire from an old toaster. The particular wire has a resistance of 25.8 ohms per metre.

I cut a piece 48 centimetres long for the objective; 37 cm for the eyepiece.

I placed a strip of black electrical tape around the barrel of the finder scope, inside out, i.e. with the sticky side out. I carefully coiled the nichrome wire around the barrel so each loop was near to the previous but not touching it. I was able to go around 4 times (both for the objective and eyepiece) while leaving about 1 cm at each end for the leads.

I layed another piece of tape, this time right-side up, sticky side down, atop the nichrome wire. I pressed the two pieces of tape together to seal the nichrome wire in place. Hopefully this approach will ensure the nichrome wires do not touch each other and short out.

On top of the heater coil, I pressed some closed-cell neoprene self-adhesive foam tape (purchased some time ago from Canadian Tire). This is to keep as much heat in as possible, instead of giving it away to the surrounding air. I placed another strip of electrical tape on the heater, around the perimeter of the foam, to hold the foam in place.

I had heard that soldering to nichrome was difficult so, to the leads of the coils, I attached tube terminals, crimping them in place. I considered attempting to solder these in place but realised this would prove futile later on.

I connected a short length of some red-jacketed 20-gauge wire between the front and rear heaters, crimping this into the terminals as well. I made sure this wire was long enough to allow for one of the heaters to be removed from the finder scope while the other one was attached. This manoeuvre will be required as the finder scope is mounted in the telescope brackets and I need to slip on or off the heater.

I remembered to pre-install on some heat shrink tubing. Fired up my heat gun (on the low setting this time) to tighten up the tubing.

Then I attached a one metre length of the professional grade 4-wire (24-gauge?) microphone cable, again using 2 wires for each side of the circuit. This I terminated with a red RCA plug.

Did a quick bench test, connected to the Kendrick dew controller, in turn, driven from the portable car battery. Works. Good heat at high power.

I look forward to trying the new custom heater during the next damp session! Bring on the dew!