I mostly agree. My thinking is that a fan that runs continuously wastes power and draws dust and dirt into the equipment. I also believe that a fan that runs only during PTT is not doing much good except on very long transmissions- when the heat of the PA has made it to the fins. It may take several minutes of key-down time before the fins start getting warm, so running the fan before then is ineffective.
My practice is to fix a normally-open thermal switch to one of the heat-sink fins, using heat-sink compound for good heat transfer. I have found that a switch that closes at 122 degrees Fahrenheit (50 degrees Celsius) works best, since it opens about ten degrees lower, and provides near-ideal hysteresis. The thermal switch directly controls a small AC or DC fan that blows on the fins. Not only is this an extremely simple solution, but it ensures that the fan will run only when needed and for as long as needed. I use a Cantherm switch that Digi-Key sells under catalog number 317- 1094-ND for about $7. 73, Eric Lemmon WB6FLY --- In Repeater-Builder@yahoogroups.com, "Chuck Kelsey" <wb2...@...> wrote: > > Maybe it's just me, but I've never understood the need for a special circuit > to run cooling fans. > > I run my fans from the PTT line using a relay. I have also used a simple > chassis thermostat, but prefer using PTT. I suppose you could easily use > both methods so that in the event that the equipment remained too warm when > PTT halts, the thermostat could keep it running longer. However, I contend > that if this is happening, your fans are inadequate and not keeping up with > the demand right along. > > Why the need to continue cooling after the QSO has ended? Just because you > can? > > Chuck > WB2EDV > > > > ----- Original Message ----- > From: "skipp025" <skipp...@...> > To: <Repeater-Builder@yahoogroups.com> > Sent: Sunday, December 21, 2008 12:24 PM > Subject: [Repeater-Builder] Re: fan timer circuit > > > > Re: fan timer circuit > > > > I've seen a number of fan delay, time on, time off circuits > > posted on web. The "neat'o web page" url I just posted here > > on the group has one and it might be the one you're looking > > for. > > > > http://www.w1ghz.org/small_proj/small_proj.htm > > > > .... and the fan controller information is about half way > > down the page with a picture and down-loadable zip file. > > > > My own personal preference is to run everything warm and even > > a lot higher temp than most of you would expect. In a repeater > > station operation only an RF PA and un-modified Astron Power > > Supply with an undersized heat sink might get a fan. Never a > > failure of a well planned installation. > > > > Some of our local "start-up" radio clubs throwing repeater > > packages in place often start out using and stay with an > > external RF amplifier designed for mobile operation. Sometimes > > the amp runs so hot you can't keep your hand on the heat sink > > but I've yet to see one fail. > > > > > > cheers, > > skipp > > >
