[Elecraft] KPS1500 fan noises

Bob McGraw K4TAX rmcgraw at blomand.net
Mon May 21 19:49:26 EDT 2018


There are basically two types of radial blade fans and specific 
application for each one.   Those that "blow" and those that "suck".  
There is a difference in the design of the fan blades and the 
application for a specific fan.   Also some are designed to have "air 
over the motor".  This is a point affecting motor life and bearing 
lubrication.

Those that "blow" are designed to pressurize a box or enclosure to a 
specific  pressure measured in inches or millibars of H²O. Reducing the 
air exhaust area or restricting air exhaust flow, thus increasing 
internal pressure, can cause a blade stall.  This actually reduces the 
amount of air measured in CFM that a given fan can deliver.

The other type  of fan, those that "suck" are designed to exhaust air 
from a box or enclosure to a specific value measured in inches or 
millibars of H²0.     There is always some amount of restriction to 
airflow entering, usually being contributed by the obstruction i.e. air 
vents,  to air entering the box.  The perforated air vent on top of the 
KPA500 as an example.

While I agree that increased airflow is beneficial to keeping 
electronics cool, one must assure that added cooling efforts do not 
create a vortex in the given area to be cooled.   This could cause a 
void of air movement and thus reduced cooling.    The KPA500 {I can't 
speak for the KPA1500} are surely engineered and evaluated {brick on the 
key}  to work within design limits of the solid state devices along with 
cooling other components.    In some cases, ones added cooling efforts 
which may actually cause a partial blade stall, same as the stall effect 
of an airplane wing, and thus cooling is actually reduced and, in many 
cases.  In some instances, overall fan noise being increased.

Take care in the application of added cooling efforts.

I run my KPA500 with the FAN CTL at Normal.   It will step through all 6 
levels as needed, otherwise it is off.    I find no reason for it to run 
all of the time at the lowest speed. Depending on mode and length of 
transmission, I find the fan comes on and will ramp up as needed.    
I've not seen any reported temperature above 65ºC with a heat sink upper 
limit of 90ºC.

73

Bob, K4TAX



On 5/21/2018 2:32 PM, Roy Koeppe wrote:
>
> "Do the KPA1500 fans push air into the box? If so, why doesn't the 
> KPA500 fan do that. If the KPA1500 fans pull out of the box why would 
> it be appropriate to use an additional fan that opposes this airflow?"
>
> Yes, they do...which is also opposite of airflow in K3s. The idea of 
> the additional fans is that they are much more quiet than the built 
> ins, even when they are on speed #1 . And they prevent the built ins 
> from running so much or not at all. Simpleminded, I admit.
>
> Roy   K6XK
>
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