[Elecraft] Fw: KPA500 - Advantage of min fan speed?

[Andy Durbin]

Don,

Two test cases -

Case 1:
Ambient temperature 28 deg C, KPA500 OPER mode but no TX in over 12 hours, fan speed zero, PA temp 35 deg C.

Case 2:
Ambient temperature 28 deg C, KPA500 OPER mode but no TX in over 12 hours, fan speed 1 run for long enough to stabilize PA temperature, PA temp 29 deg C.

Fan 1 continuous operation has pre-cooled the KPA500 PA by 6 deg C (measured data).

It's obvious that that the start of the the first high power "run" cycle will have a later onset of fan 2 if the KPA500 has been pre-cooled at FS 1.  What is not obvious is whether there will be any sustained advantage if the "run" continues.  If the "run" never allows the temperature to drop to fan  speed 1 there would appear to be no operational advantage to the pre-cool at fan speed 1.

For a S&P duty cycle each TX would likely have delayed fan speed increases.  However, that advantage has to be offset by the noise of fan 1 when no cooling was required.

Andy, k3wyc




________________________________
From: Don Wilhelm <donwilh at embarqmail.com>
Sent: Monday, September 30, 2019 10:28 AM
To: Andy Durbin <a.durbin at msn.com>; elecraft at mailman.qth.net <elecraft at mailman.qth.net>
Subject: Re: [Elecraft] KPA500 - Advantage of min fan speed?

Andy,

Physical fact related to any heat dissipating object -- if you apply an
air stream across the object, it will not come up to a given temperature
as quickly as having no air stream across it.

Specifically for the amp, if you run the fan speed minimum at 1, it will
heat to the 55 degC threshold more slowly before switching  to level 2.
Of course, from there on up to higher temperatures, there will be the
same time period between the higher fan speed steps.

In other words, the fan minimum will NOT shift the entire range of
thresholds, but it WILL delay the time to reach the level 2 threshold.

73,
Don W3FPR