Thermostatically Controlled Fan for OrionI/II

Posted to Ten-Tec Reflector June 2, 2011

I just recently acquired my Orion II and was surprised that the optional cooling fan that was installed ran all the time. My other transceivers going back 20 years all had thermostatic fan control so you didn't have to listen to the fan running if you're just listening to the receiver.

While combing through the Far Circuits stuff at Dayton, I picked up one of their little circuit boards for building a thermostatic fan controller. The circuit is from an article in June 1994 QST by Bertram Kolts, WA0WZI, titled: "An Automatic Temperature-Controlled Fan" and I've used it a few times in the past, usually building it on a small piece of perf board.

This provides a no-holes, plug-in mod that I used to prevent the Orion fan from running unless the heat sink reaches the adjustable turn-on temperature. I secured the board to the side of the fan housing with velcro, and the fan gets its power from the board which gets its power from the 13.8V jack you'd plug the fan into normally. The only other item to mount is the thermistor, which you can glue into a 1/2" long, 1/4" diameter piece of metal tubing, which is then force-fit between the two top fins on the heat sink. The Orion fan mounting bracket is such that air is not drawn between those two fins, so the thermistor will not be cooled directly by the fan's air flow.

The circuit includes a temperature set mini-pot on the board and I set it so that the fan is off after the Orion has been powered on for several hours. With that setting, the fan came on a couple of times during operation in the CQ WPX CW contest. It would be easy to adjust the pot so that the fan comes on only when operating the digital modes for extended periods.

Total cost would be in the area of $15 even buying everything new. The mod can be easily removed, leaving no trace.

73, Floyd - K8AC

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