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Re: KPS1500 fan noises

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Roy Koeppe

Re: KPS1500 fan noises

"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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Clay Autery-2

Re: KPS1500 fan noises

Roy, contrary to what the other guy said, that is a perfectly logical
supplement to the OE cooling system. ANYTHING that reduces the pressure
at the exit venting will improve airflow over the heatsink.
Increase inlet and exit free area and/or increase inlet pressure or
reduce outlet pressure..... all will increase flow volume.

Alternatively/additionally, the industrious owner might also consider a
custom duct in the back that would provide for adding multiple 120mm or
140mm high-quality fans set to blow air IN. I prefer Noctua fans these
days. They are quiet, come with anti-vibration mounts built in, and
there are full anti-vibe gaskets available on some models that prevent
flow short circuits. They also come in 3-pin or 4-pin models. 3-pin
models can generally be set to run at full speed or at 1 or 2 slower
speeds. The trick solution would be to use 4-wire fans and your own
feedback loop controller to adjust the speed dynamically..... albeit,
you need to test and modify any of the ready-built controllers to make
sure you aren't broadcasting RF birdies with the PWM.

The benefit to putting fans in back blowing through the stock
screen/fans is that you get the slight added benefit of over-pressuring
the chassis which tends to keep the chassis interior cleaner. Assuming
adequate rear spacing, you can hide the fans a bit more....

I could go on... I love thermal control stuff... I'd be interested to
see the numbers on how much power/heat is dissipated at 1500W key down...

73,

______________________
Clay Autery, KY5G
(318) 518-1389

On 05/21/18 14:32, Roy Koeppe wrote:

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Bob McGraw - K4TAX

Re: KPS1500 fan noises

In reply to this post by Roy Koeppe

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
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to [hidden email]
>