[Elecraft] Cooling in the K2

[David Robertson]

With due respect to both Ken and Bill

Ref below:
 I used a 5 volt regulator on my MFJ 4225 to slow down the fan. This allows
>> the fan to start reliably at any voltage. I have run mine and my K2-100 this
>> way for at least 5 years with no problem on SSB, CW and DIGITAL.
>>
>> 73
>> Ken W0CZ
>>
>> Bill NZ0T Wrote
>> <As I'm not a very technical person I just used a couple of resistors in
>> <parallel to slow the fan down in my 4225.  I can't remember the values this
>> <early in the morning but it seems to be working just fine.  The supply does
>> <run a little warmer but not hot and the fan is no longer heard.
>> <
>> <Bill NZ0T

The K2 fan has two major differences in cooling then the K3 fans.

1, The K2 fan is much smaller and has limited air flow capacity then the two larger K3 fan(s).

2, The k2 Fan cools only the underside of the heat sink and components mounted nearby. It's cooling capacity is greatly diminished when cooling the KPA-100's heat sink.. (mounting an 80 MM fan on top of the K2 really helps). In addition the K2's fan really only removed the hea fro beneath the KPA100 heat sink.  In normal operation when you are making large demands of your 100 watt amplifier that little K2 fan has GOT to move a lot of air thus will make noise.

The K3 cooling fans draws needed amounts of cool air from the top of the K3's case (which means it is not a good place for a book or magazine to be resting when operating). The air flow directly draws air over the K3's power amplifier heat sinks and underside components at the same time and exhausts the hot air out the rear. This results in much more efficient cooling with relative slow fan rotational speed. 

In a test I ran my K3 key down with 100 watts out in a dummy load  for 15 minutes. I could only could barely hear the fans though there was lots of warm air coming out of the rear vents.

It also may be a good idea to order some spare fans from Elecraft or directly from the manufacturer with the same model number. They get dirty and go bad in time.

Because Elecraft electronically controls it's fan speed by either adjusting the fan's operating voltage or duty cycle pulses. Using a "Temperature controlled fan has a good chance of working against the Elecraft fan control speed because Elecraft controls fan speed by heat sink temperature, not air temperature at the fan itself.

Silent fans are designed to operate at slower speeds which reduce nose but when Elecraft needs lots of cooling these quiet fans cannot put out the needed flow



The bottom line is don't miss with the K2 fan speed in any way which could reduce it's speed. You are looking for trouble if you do. I would leave the K3 fans alone also.

If you have a lot of fan noise usually it a result of a misplaced wire or a bad fan.

I work on a lot of computer systems and have lots of experience with cooling fan problems

73
KD1NA

PS I really love my Elecraft K2 and K3

.