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.
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