A rail-mounted enclosure for a Telescope Dew Heater PWM Controller. The rail clip was designed to slide onto the Celestron NexStar 8SE dovetail rail, but may fit others (friction should keep it from sliding). The enclosure cover should slide into the slot (also meant to be held on by friction; the cover in the STL file is scaled to 98.5% of the opening size but fit will depend on the print quality).

The mini PWM controller was purchased from Amazon. I hot-glued a female barrel connector inside, lined up with the Vin hole. For Vout, I used a cable with a male barrel connector on the end that plugs into my Celestron dew heater ring. There are no air holes in the box, on the assumption that the PWM doesn't get too warm.

SCAD file attached for additional customization.

Celestron dew heater ring I'm using with this:
https://www.celestron.com/products/dew-heater-ring-8in

NOTE that there is a red LED on many PWM controller boards, including the one in my photo. You may want to cover it before you put the lid on, or use a darker filament color, if you prefer that the enclosure isn't glowing when the dew heater is on.

Incidentally, do you know why it's better to use a PWM instead of just a variable resistor to control the dew heater? Answer: Because with a variable resistor, much of the heat would be dissipated by the resistor instead of by the dew ring. For example, if the resistor was the same resistance as the dew heater ring, there would be 6V across the dew heater ring and 6V across the resistor, and half of the heat would be dissipated by the resistor. In contrast, a PWM set to 50% duty cycle provides a near 12V-peak-to-peak square wave to the dew heater, producing the same amount of heat in the dew ring, with very little energy wasted in the PWM itself since it's low resistance in the On state.