Re: Re: [Repeater-Builder] What PA temp is too much?

Thu, 17 Feb 2005 14:36:47 -0800

I have another solution.  AirPax makes a TO-22 style snap switch in the 6700 series.  Can be NO or NC and you can order the temp you want.  Newark has them for about $7.50.  I would mount it on the stud for the RF device if you can.  That way, the temperature of the device is monitored and not the thermal resistance of the mount and heat sink.  A thought.

[EMAIL PROTECTED] wrote:


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 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/
> >
> > *
> > * To unsubscribe from this group, send an email to:
> > *
> > [EMAIL PROTECTED]
> >
> > *
> > * Your use of Yahoo! Groups is subject to the
> > 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/




Do you Yahoo!?
Yahoo! Search presents - Jib Jab's 'Second Term'






Yahoo! Groups Links

Reply via email to