I went this road a few years ago using the small button thermal switches (Switch Craft - etc.) that are available in a variety of on-off temperatures settings, but it didn't prove overly successful. The small thermal switches have to be heat sinked to the PA, so you have to route AC for the fan up to some location on the PA heat sink, this is messy, not easy to implement, and requires extra AC (hum) wiring running around the station. The switches don't have an impressive life cycle and many started going intermittent and erratic in a year or so. The new approach I implemented is to use a solid state relay, they require nothing more than a logic level to drive them, which is easy to find about anywhere in the station or controller (most controllers have logic outputs that can be controlled by writing a simple macro command controlled by the PTT command). This isn't temp controlled, its time controlled, so fan comes on with PTT command from the controller, fan continues to run for 4 minutes after PTT drops. ( I use this control scheme for PA and general cabinet fan cooling operations on all my repeaters using SCOM 7K controllers) This has proven much more reliable over time than temp. control and you will likely find the fans can do many more on-off cycles during their usable life than the thermal switches. Solid state relays last a lifetime and cost less than the thermal snap disc switches in many cases. The fan starts PA cooling process w/o waiting for PA to heat up before cooling can start and then try and play catch up; a 3 to 4 minute post PTT run time on the fan is plenty of time to allow for more than sufficient cool down of any residual heat; this is where a thermal control switch can often cycle on-off several times depending on the proximity of the thermal switch-fan-main heat sources, and size/density of the heat sink. The power consumption of a good muffin fan is about 4 to 8 watts, so even if you have more run time using the timer approach it isn't going to amount to 20 cents of electricity a month and you end up with something from my experience which has proven much more reliable in the long run. A side benefit to having the fan come on with PTT other than PA cooling is it supplies immediate air movement inside the cabinet for some cooling to the power supply, circulators, etc. So hope this is some help or insight for your application - Good Luck
Rob K7EI -----Original Message----- From: dave_g7uzn [mailto:[EMAIL PROTECTED] Sent: Tuesday, April 06, 2004 9:02 AM To: Repeater-Builder@yahoogroups.com Subject: [Repeater-Builder] Thermostaticaly controlled fan cctt please ? Hi All, Can anyone point me in the right direction for a site with a variable temp controlled fan cctt please for use on mobiles/base stns please ? Any help appreciated.....Cheers Dave UZN Yahoo! Groups Links Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/Repeater-Builder/ <*> To unsubscribe from this group, send an email to: [EMAIL PROTECTED] <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
