Re: K3 cooling fan cycling

Posted by Guy, K2AV on Apr 13, 2011; 9:10pm
URL: http://elecraft.85.s1.nabble.com/K3-cooling-fan-cycling-tp6270057p6270674.html

> As I understand it, the K3's final transistors are quite robust with
> regard to temperature.

The transistors are robust temperature-wise because they are so
heavily heat-sinked and heavily fanned, and the fans dig in quickly to
hold the line with small temp differences.  Off the heat sink those
transistors will go toast at about the same temp as other kinds.

Your suggestion of spreading out the speed increases will undo the
stepped fan/heatsink dissipation holding the transistors at a narrow
temperature range until the fourth speed has cut in.  This design is
not too unlike the function of an automobile radiator thermostat which
varies the speed of water circulation with the BTU heat output of the
engine. The radiator thermostat actually goes from almost closed to
full open in something like 15 degrees. The narrow temp range is by
design, on purpose in both the K3 and automotive case.

Running the fans at speed 1 or 2 all the time will postpone the
transistors arriving at the narrow temp zone. Running transistors
cooler won't hurt them that I know of.  In the automotive case running
the engine colder lowers fuel mileage.

> The thermal Achilles heel of the K3 appears to be
> the amplifier's multipin connector, at least according to other posts.

The pins in question for some time now have been converted to gold
plated.  The issue was corrosion causing raised contact resistance
which then overheated to the point of oxidizing to non-conduction.
Currently shipping units and retrofitted units do not have this
problem.

> The fans don't seem to be able to cool that connector adequately.  Less
> fan cycling will neither solve nor exacerbate that problem.

The pin corrosion issue is in no way related to the fans.  Onset of
the pins becoming non-conductive often happened first when the rig was
stone cold.  Refer to the web site's public list of modifications for
further information.  Dinking with the fan speed is NOT a means of
addressing the old pin problem.

73, Guy

>
> 73, Paul W8TM
>
> ***********************
>
> K2AV sed:
> If cycling bothers you try setting CONFIG:KPA3 to FAN1 or FAN2.  If
> you are operating SSB, that may remove most cycling.  This adjustment
> sets the MINIMUM fan speed.  "NOR" is fan off until called for.
>
>
>
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