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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