My solution is an LM34 expoxied to the hottest part of the heatsink (For a T44, 4th-5th fin in from the right viewed from the back) connected to a PIC 12C675 microprocessor. The firmware in the PIC turns the fan on at 100 degrees F when there is PTT present, and runs it for 2 1/2 minutes before checking it again. If the temperature exceeds 140 degrees F, the PIC will interrupt the PTT line to the transmitter. My T44's stabilize at 104-107 degrees F with a 26CFM blower and duct directing the blower's flow over across all heatsink fins. The heatsink temperature stabilizes to 104-115 degrees at ambient (70-75 degrees F.).
Steve WA6ZFT > > From: Mike Morris WA6ILQ <[EMAIL PROTECTED]> > Date: 2005/02/17 Thu PM 01:26:12 EST > To: [email protected] > Subject: Re: [Repeater-Builder] What PA temp is too much? > > On the radios that do not have a flat, open heat sink surface > near the final transistor I drill and tap the base of the > exposed fin nearest to it. A drop of heat sink compound > between the thermal switch and the fin also helps the > responsiveness of the sensor... > > I've also seen a fan control diagram somewhere that used > a thermistor mounted along with the fan switch. The > CMOS timer was that chip that had the oscillator and a > dozen or so stages of divide-by-two. The thermistor was > wired in the RC network so that the hotter it got the longer > the timeout period was. This kept the fan on longer the > hotter the thermistor got. > The timer was set up to start with PTT and when it was > released the timing period started. The minimum was > 4 to 5 minutes, the longest was a few hours. > > A second fan switch set at a higher temperature turned > on second fan, in case the first fan died. The switch also > keyed a digital input on the controller, which changed the > courtesy beep from a single beep (normal) to 4 beeps > (Morse "H", meaning HOT). > > Mike WA6ILQ > > At 09:44 AM 2/17/05, you wrote: > > >OK, well I was going to incorporate a fan also onto the heatsink, which I > >had already planned but didn't mention. The fan is activated by the > >controller and comes on when the PTT activates and goes off 1 minute after > >the PTT drops. But, I have a feeling that the fan I have will not be > >adequate for long transmissions, but I am not sure. So I was going to > >hook up the thermal warning to the controller since I had a spare digital > >input. So, now with knowing I am using a fan, where on the heatsink > >should I place the sensor. Should I put it right near the heatsink bolt > >on the transistor or should I put it on on of the fins. I think closer to > >the transistor bolt, but let me know your thoughts. > > > >Larry, N8RDT > > > >[EMAIL PROTECTED] wrote: > >Henry Radio uses 125 degree thermo-switches on their commercial amps. If > >you check out their web page they sell the switches for $9.50 The > >switches are used to activate 12-V cooling fans on their amps. > > > > > > > > > > > > > >Do you Yahoo!? > >The <http://my.yahoo.com>all-new My Yahoo! � Get yours free! > > > > > > > > > > > > > > > >---------- > >Yahoo! Groups Links > > * To visit your group on the web, go to: > > * > > <http://groups.yahoo.com/group/Repeater-Builder/>http://groups.yahoo.com/group/Repeater-Builder/ > > > > > > * > > * To unsubscribe from this group, send an email to: > > * > > <mailto:[EMAIL PROTECTED]>[EMAIL PROTECTED] > > > > * > > * Your use of Yahoo! Groups is subject to the > > <http://docs.yahoo.com/info/terms/>Yahoo! Terms of Service. > > 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/
