[Elecraft] KPA100 Temp/Fan

[Don Wilhelm]

Jim,

The fan does go on and off by sensing the temperature of the heat sink 
(Q3 is the sensing element).
The temperature that the fan transition occurs is fixed, but will 
operate at that fixed temperature only if CAL TPA is set correctly.  CAL 
TPA must be set to the actual temperature of the heat sink, and that is 
easily done by allowing the KPA100 to cool (an hour or more) to the 
ambient temperature and setting the parameter to match the ambient 
temperature (in degrees C).

If you think the fan is coming on too soon, you might try running the 
fan at the Hi/Lo setting rather than normal - the fan is not very noisy 
at low speed.  Another solution is to add a muffin fan on top of the 
heat sink to draw air away from it - the means of keeping the fan in 
place can vary - if the KPA100 is not tilted, it will likely just sit 
there unaided, but if tilted, some fastening device may be required.  
You can see Tom Hammond's implementation at www.n0ss.net.  The speed of 
an external 12 volt DC fan (salvaged from a defunct PC) can be slowed by 
inserting a series resistor.

73,
Don W3FPR

Jim Stoneback wrote:
> I searched the archives and didn't find anything on this, but from 
> what I've read, I think I may have a problem with my KPA100.  When 
> operating CW the fan turns on high during every transmission and the 
> heat sink gets hot to the touch.  I'm a ragchewer so my transmissions 
> do run to several minutes and, regardless of power setting, the fan 
> will kick on high after several minutes of transmitting.  Fan is set 
> to 'nor'.  Sending speed ranges from 15-20 wpm.  Ambient temperature 
> in the shack is around 74F.  The fan has never kicked up to high when 
> on SSB but I don't operate fone much, and generally don't talk for 
> very long when I do.  The K2/100 (recent build, sn 6194, KPA100 
> Version F1.10) operates well in all other respects.  Does anyone have 
> an idea what may be wrong?
>
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