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Don Rasmussen

K3 Cooling

Don (FPR type),

Do you really think it matters in K3 - with micro fan motors and such a simple cage?

If a K3 is setup to run TX RTTY in a controlled environment,
and then repeat the test with the fan direction reversed, how much
of a temperature delta would you expect?

[Elecraft] K3 Cooling
Don Wilhelm w3fpr at embarqmail.com
Mon Apr 5 15:20:41 EDT 2010

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--------------------------------------------------------------------------------

Don,

In my fluid mechanics labs it became apparent that exhaust cooling is
much more effective than forced cooling for situations that are similar
to the K3 PA 'cage'.
First is that the exhaust fan does not add to the temperature of the
air, and second, the flow can be more easily controlled. The exhaust
fans remove heated air from the hottest spots - who cares where the
cooler makeup air comes from, it can be supplied from any vent holes in
the cabinet.

As humans, this is counter-intuitive because we feel cooler with air
blowing onto us, but that is mainly because of evaporation cooling, not
air flow. We do not usually feel cooler standing on the other side of a
fan. Electronics do not have that evaporative cooling effect (unless
you have poured a liquid on the electronics!), so in most cases, exhaust
cooling near the heated areas does a better job.

If you question the fact that a fan adds heat to the air-stream, measure
the temperature on the upstream side of a fan and the downstream side.
I can assure you that the downstream air is warmer - the fan provides
work to move the air, so it must heat the air because of that work-force
(it is not the heat of the fan motor that I am referring to, but the
motor heat may be present too.

One can design to contain the flow on the downstream side of the fan,
but I see no air channel (pipe) in the K3 to accomplish that. With old
vacuum tube designs, we often used fans to pressurize the area below the
chassis and direct the flow up around the tubes with chimneys around the
tubes.

73,
Don W3FPR

Don Rasmussen wrote:
> I've seen this thread on every ham list I've read - goes on forever.
>
> I always wonder - how does the K3 know which are the intake holes in the cabinet and which are exhaust? The cool air comes in replacing the hot air, right? ;-)
>
> On tube transceivers, the finals may be oriented at the rear of the chassis near the fan, so a pulling fan will bring the cool air to the finals first, then that warmed air goes to the rest of the smaller tubes on the chassis. Reverse the air flow, the finals dont get the room temp air first, the smaller tubes on the chassis do. This -may- be important on some rigs, guess it depends. I have the Drakes setup for exhaust.
>
> K3 has these fins. I am going to take a poll with my fins and find out which ones care about the direction of the air travelling across them. ;-)
>
>

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lstavenhagen

Re: K3 Cooling

Dont mean to jump in but I'd be the difference would be significant. Air flow into a low pressure area causes it to expand and thus cool down (similar to the heat exchange method used in air conditioners), and the reverse for air stuffed into a high pressure area (compresses, heats up).
Also, in any air cooling system the most important item is arguably the design of the _exhaust_ port - it has to be configured in such a way as to most efficiently produce a pressure differential (which is what actually moves the air) in area of the thing you need to keep cool. This is a critical design factor in engine cooling systems in aircraft for example (interestingly enough, most of the attention is on the holes in the bottom/side/top of the cowling, not the big holes in the front).

In the K3 box, it doesn't look like air getting pushed in from the back has as many clean escape areas as it would the other way around. Just eyeballing mine that is. But even if so, you still have to consider the contribution of the heat exchange situation introduced by the fan in all that too.

I'd be willing to bet it'd be a noticeable difference....

73,
LS
W5QD

Don Wilhelm-4

Re: K3 Cooling

In reply to this post by Don Rasmussen

Don,

I suspect it would make a big difference, especially with the SubRX
installed - it would be worse with the air flow inward.
In order to provide effective cooling, the air flow needs to be laminar
across the heat sink. If there is turbulence, the cooling effectiveness
will be reduced. By blowing air onto the heat sink, first each fin
would create its own bit of turbulence as the air strikes it, and then
when the air flow reaches the blockage presented by the SubRX enclosure,
additional turbulence is bound to occur, and that would create
backpressure for the movement of the air stream. More turbulence means
less cooling. With the exhaust fans, the air will come from wherever it
can within the K3 enclosure and should flow in a more laminar fashion
toward the fans, and then exit at the back.

Again, I believe this is counter-intuitive to our normal senses. If we
were to stick a finger into the air path, it would seem like the air is
cooler if it is blowing on our finger. The heat sink cooling is
different than the sensation of our finger, cooling of a surface is
highly dependent on a laminar flow where our 'finger test' would surmise
that the turbulent flow should cool better.

Because of the effects of turbulence, there is also a point of
diminishing returns when increasing the air flow with faster fans.
Turbulence can also be created with exhaust fans, but not as readily
(per volume of air moved) as with air pumped into the assembly.

I have not done any air flow studies of my K3 cooling, and I don't know
to what extent Elecraft has done that during the development process,
but it seems to be quite OK. The highest temperatures I have seen
reported is somewhere in the vicinity of 60 to 65 deg C, and if I recall
correctly, Eric has stated that there is no problem below 80 deg C.
(Someone correct me on that number if my memory is not correct).
15 deg C is a lot of margin.

73,
Don W3FPR

Don Rasmussen wrote:

> Don (FPR type),
>
> Do you really think it matters in K3 - with micro fan motors and such a simple cage?
>
> If a K3 is setup to run TX RTTY in a controlled environment,
> and then repeat the test with the fan direction reversed, how much
> of a temperature delta would you expect?
>
> [Elecraft] K3 Cooling
> Don Wilhelm w3fpr at embarqmail.com
> Mon Apr 5 15:20:41 EDT 2010
>
> Previous message: [Elecraft] K3 Cooling
> Next message: [Elecraft] sound card recommendations
> Messages sorted by: [ date ] [ thread ] [ subject ] [ author ]
>
> --------------------------------------------------------------------------------
>
> Don,
>
> In my fluid mechanics labs it became apparent that exhaust cooling is
> much more effective than forced cooling for situations that are similar
> to the K3 PA 'cage'.
> First is that the exhaust fan does not add to the temperature of the
> air, and second, the flow can be more easily controlled. The exhaust
> fans remove heated air from the hottest spots - who cares where the
> cooler makeup air comes from, it can be supplied from any vent holes in
> the cabinet.
>
> As humans, this is counter-intuitive because we feel cooler with air
> blowing onto us, but that is mainly because of evaporation cooling, not
> air flow. We do not usually feel cooler standing on the other side of a
> fan. Electronics do not have that evaporative cooling effect (unless
> you have poured a liquid on the electronics!), so in most cases, exhaust
> cooling near the heated areas does a better job.
>
> If you question the fact that a fan adds heat to the air-stream, measure
> the temperature on the upstream side of a fan and the downstream side.
> I can assure you that the downstream air is warmer - the fan provides
> work to move the air, so it must heat the air because of that work-force
> (it is not the heat of the fan motor that I am referring to, but the
> motor heat may be present too.
>
> One can design to contain the flow on the downstream side of the fan,
> but I see no air channel (pipe) in the K3 to accomplish that. With old
> vacuum tube designs, we often used fans to pressurize the area below the
> chassis and direct the flow up around the tubes with chimneys around the
> tubes.
>
> 73,
> Don W3FPR
>
> Don Rasmussen wrote:
>
>> I've seen this thread on every ham list I've read - goes on forever.
>>
>> I always wonder - how does the K3 know which are the intake holes in the cabinet and which are exhaust? The cool air comes in replacing the hot air, right? ;-)
>>
>> On tube transceivers, the finals may be oriented at the rear of the chassis near the fan, so a pulling fan will bring the cool air to the finals first, then that warmed air goes to the rest of the smaller tubes on the chassis. Reverse the air flow, the finals dont get the room temp air first, the smaller tubes on the chassis do. This -may- be important on some rigs, guess it depends. I have the Drakes setup for exhaust.
>>
>> K3 has these fins. I am going to take a poll with my fins and find out which ones care about the direction of the air travelling across them. ;-)
>>
>>
>>
>
>
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W8JI

Re: K3 Cooling

Let me throw a few things into the mix.

1.) About compression and temperature. There isn't enough
pressure to make a difference. The fan in the K3 is not
running at 40 PSI, or even at 0.4 PSI. I would bet the
static pressure is less than 0.1 inches of water (.0036
PSI). It takes a pretty big centrifugal blower to make .036
PSI (1 inch of water), and the heating from that pressure is
negligible.

2.) We really don't want laminar flow across a heatsink. We
want some turbulence so the air isn't stagnant along the
fins. The AL600 and ALS1300 have deflectors that add
turbulence because the fins are 6" long, straight, smooth,
flat, and far from the fans. Adding deflectors to create
turbulence almost doubled the cooling. I doubt this is the
case with the K3.

3.) I would not blow hot air from a heatsink or high
dissipation area into the more sensitive electronics, nor
would I do anything the engineers at Elecraft didn't suggest
or approve. Generally people designing air systems know far
more about the systems than casual observers. If I wanted a
cooler heatsink and was left to my own devices, I would
change to a higher airflow fan of the same style. I can see
all sorts of problems that might occur from reversing, and
even a few from adding a "blow into the case" helper fan.

The heatsink is probably warming the air with 150 watts of
heat dissipation at times. I haven't looked at current drawn
by the rest of the radio, but I doubt the other components
in the radio dissipate 25 watts total. Why would I blow a
150 watt heater into a 25 watt heated area? It would make a
whole lot more sense to draw the slightly heated air across
the heatsink than bake the rest of the radio.

73 Tom

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Guy, K2AV

Re: K3 Cooling

In reply to this post by Don Rasmussen

I believe that if you examine the intake slots above the PA heat sink,
you will see that cool intake will come in equally across the fins,
with the fins farthest from the fans getting cool air directly from
above, and the portion of fins closest, though pulling warm air from
parts of the fins away from the fans, pulls the air with increasing
velocity as the fans are approached, cooling the heat sink near
equally. That does NOT happen if the flow is reversed as the fins
farthest away get the LEAST velocity with the hottest air. Flow
should definitely PULL over the fins and exhaust out the back.

In a minor disagreement with Don, I think that the unequal cooling is
the killer issue not the fan raising the air temp blowing in.

I'm not going to do it on mine (I like it working), but if someone
actually reverses that and goes, I'd guess +10 to +20C in the temp and
kicking in the overtemp protection.

As to how good the cooling is, just to see what happened, I let the K3
transmit at 100 watts for a half hour into a dead band. It never hit
60C. I set there watching it the whole time waiting for a temp spike
that never happened. It got up to the high fan speed and blew fairly
warm air out the back, but stayed steady. K3 is brick on key.
Something must be correctly engineered.

After that was over it occurred to me that I could have fried my
Astron RS35A, but that held up as well. : >)

73, Guy.

On Mon, Apr 5, 2010 at 7:08 PM, Don Rasmussen <[hidden email]> wrote:

> Don (FPR type),
>
> Do you really think it matters in K3 - with micro fan motors and such a simple cage?
>
> If a K3 is setup to run TX RTTY in a controlled environment,
> and then repeat the test with the fan direction reversed, how much
> of a temperature delta would you expect?
>
> [Elecraft] K3 Cooling
> Don Wilhelm w3fpr at embarqmail.com
> Mon Apr 5 15:20:41 EDT 2010
>
> Previous message: [Elecraft] K3 Cooling
> Next message: [Elecraft] sound card recommendations
> Messages sorted by: [ date ] [ thread ] [ subject ] [ author ]
>
> --------------------------------------------------------------------------------
>
> Don,
>
> In my fluid mechanics labs it became apparent that exhaust cooling is
> much more effective than forced cooling for situations that are similar
> to the K3 PA 'cage'.
> First is that the exhaust fan does not add to the temperature of the
> air, and second, the flow can be more easily controlled. The exhaust
> fans remove heated air from the hottest spots - who cares where the
> cooler makeup air comes from, it can be supplied from any vent holes in
> the cabinet.
>
> As humans, this is counter-intuitive because we feel cooler with air
> blowing onto us, but that is mainly because of evaporation cooling, not
> air flow. We do not usually feel cooler standing on the other side of a
> fan. Electronics do not have that evaporative cooling effect (unless
> you have poured a liquid on the electronics!), so in most cases, exhaust
> cooling near the heated areas does a better job.
>
> If you question the fact that a fan adds heat to the air-stream, measure
> the temperature on the upstream side of a fan and the downstream side.
> I can assure you that the downstream air is warmer - the fan provides
> work to move the air, so it must heat the air because of that work-force
> (it is not the heat of the fan motor that I am referring to, but the
> motor heat may be present too.
>
> One can design to contain the flow on the downstream side of the fan,
> but I see no air channel (pipe) in the K3 to accomplish that. With old
> vacuum tube designs, we often used fans to pressurize the area below the
> chassis and direct the flow up around the tubes with chimneys around the
> tubes.
>
> 73,
> Don W3FPR
>
> Don Rasmussen wrote:
>> I've seen this thread on every ham list I've read - goes on forever.
>>
>> I always wonder - how does the K3 know which are the intake holes in the cabinet and which are exhaust? The cool air comes in replacing the hot air, right? ;-)
>>
>> On tube transceivers, the finals may be oriented at the rear of the chassis near the fan, so a pulling fan will bring the cool air to the finals first, then that warmed air goes to the rest of the smaller tubes on the chassis. Reverse the air flow, the finals dont get the room temp air first, the smaller tubes on the chassis do. This -may- be important on some rigs, guess it depends. I have the Drakes setup for exhaust.
>>
>> K3 has these fins. I am going to take a poll with my fins and find out which ones care about the direction of the air travelling across them. ;-)
>>
>>
>
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
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Rick Prather

Re: K3 Cooling

On 4/5/2010, at 9:11 , Guy Olinger K2AV wrote:
> >> Snip
> As to how good the cooling is, just to see what happened, I let the K3
> transmit at 100 watts for a half hour into a dead band.

>>

I wish you had said "In to a dummy load"..

As an aside, it's amazing how many engineering papers a simple question about which way the fans should be blowing in the OP's K3 can generate!

Rick
K6LE

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Brett Howard

Re: K3 Cooling

I don't get why it needs to generate any papers or studies or anything.
Its a really easy experiment to do. Transmit into a known load and plot
temperature rise vs time. Do it under the same conditions and better
yet do each experiment several times and average results. Then all you
have to do install the fans in the direction that generated the best
performance. I'd even be willing to bet that Elecraft did just this.

~Brett (KC7OTG)

On Mon, 2010-04-05 at 21:40 -0700, K6LE wrote:
> wish you had said "In to a dummy load"..
>
> As an aside, it's amazing how many engineering papers a simple
> question about which way the fans should be blowing in the OP's K3 can
> generate!

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W8JI

Re: K3 Cooling

I don't get why it needs to generate any papers or studies
or anything.
Its a really easy experiment to do. Transmit into a known
load and plot
temperature rise vs time. Do it under the same conditions
and better
yet do each experiment several times and average results.
Then all you
have to do install the fans in the direction that generated
the best
performance. I'd even be willing to bet that Elecraft did
just this. >>>

That tells us **nothing** about the temperature of other
components in the radio. It only tells us about the PA at
the point where temperature is being sensed.

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Grant Youngman

Re: K3 Cooling

In reply to this post by Brett Howard

I suspect, like any good engineering team, they did it during design. I'd be really surprised if they just did it to verify if their design was any good :-)

Grant/NQ5T

On Apr 6, 2010, at 4:35 AM, Brett Howard wrote:

> I don
> yet do each experiment several times and average results. Then all you
> have to do install the fans in the direction that generated the best
> performance. I'd even be willing to bet that Elecraft did just this.
>

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alsopb

Re: K3 Cooling

In reply to this post by W8JI

Cooling of the amp aside, blowing 60C air from the amp into the other
components (off and on) doesn't seem like what one would want to do!

73 de Brian/K3KO
Tom W8JI wrote:

> I don't get why it needs to generate any papers or studies
> or anything.
> Its a really easy experiment to do. Transmit into a known
> load and plot
> temperature rise vs time. Do it under the same conditions
> and better
> yet do each experiment several times and average results.
> Then all you
> have to do install the fans in the direction that generated
> the best
> performance. I'd even be willing to bet that Elecraft did
> just this. >>>
>
> That tells us **nothing** about the temperature of other
> components in the radio. It only tells us about the PA at
> the point where temperature is being sensed.
>

Bob McGraw - K4TAX

Re: K3 Cooling

In reply to this post by Rick Prather

OH heavens, the idea to transmitting into a "dead band" for an hour would
most assuredly be considered a violation of FCC regulations. Yes, a dummy
load should always be used for any type of testing.

As to fans, they either BLOW or SUCK, your choice. A fan with blades
performs better sucking or evacuating a cavity while a centrifugal type
blower or a fan with vanes will be better suited for pressure applications.
In any event, all fans are noisy either due to tip speed of the blades or
bearing noise of the motor. Convection or conduction cooling is much
preferred.

73
Bob, K4TAX

----- Original Message -----
From: "K6LE" <[hidden email]>
To: "Elecraft Elecraft" <[hidden email]>
Sent: Monday, April 05, 2010 11:40 PM
Subject: Re: [Elecraft] K3 Cooling

>
> On 4/5/2010, at 9:11 , Guy Olinger K2AV wrote:
>> >> Snip
>> As to how good the cooling is, just to see what happened, I let the K3
>> transmit at 100 watts for a half hour into a dead band.
>
>>>
>
> I wish you had said "In to a dummy load"..
>
> As an aside, it's amazing how many engineering papers a simple question
> about which way the fans should be blowing in the OP's K3 can generate!
>
> Rick
> K6LE
>
>
>
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
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>
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> Please help support this email list: http://www.qsl.net/donate.html
>

Rick Prather

Re: K3 Cooling

I dislike fan noise in my shack, one of the many reasons I love my iMac, and before I considered a K3 I made a trip to Aptos and they were kind enough to let me play with one for a bit including running the fans through their paces.

Then, and now on my own K3, I find it nearly impossible to hear the first 3 speeds and the 4th speed is barely detectable. That, plus the fact the the fans rarely come on at any speed means the K3 passes my personal "quiet test".

Rick
K6LE

On 4/6/2010, at 6:22 , Bob McGraw - K4TAX wrote:

> >>>Snip
> In any event, all fans are noisy either due to tip speed of the blades or
> bearing noise of the motor. Convection or conduction cooling is much
> preferred.
>
> 73
> Bob, K4TAX
>

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Guy, K2AV

Re: K3 Cooling

There was some serious engineering going on there. It would have been
SO easy to save some money and cut down on the fin size, and leave the
cabinet room for something else. It's clear that the temperature
performance was a priority in the design.

73, Guy.

On Tue, Apr 6, 2010 at 10:43 AM, Rick Prather <[hidden email]> wrote:

> I dislike fan noise in my shack, one of the many reasons I love my iMac, and before I considered a K3 I made a trip to Aptos and they were kind enough to let me play with one for a bit including running the fans through their paces.
>
> Then, and now on my own K3, I find it nearly impossible to hear the first 3 speeds and the 4th speed is barely detectable. That, plus the fact the the fans rarely come on at any speed means the K3 passes my personal "quiet test".
>
> Rick
> K6LE
>
> On 4/6/2010, at 6:22 , Bob McGraw - K4TAX wrote:
>
>> >>>Snip
>> In any event, all fans are noisy either due to tip speed of the blades or
>> bearing noise of the motor. Convection or conduction cooling is much
>> preferred.
>>
>> 73
>> Bob, K4TAX
>>
>
> ______________________________________________________________
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Eric Swartz - WA6HHQ

Re: K3 Cooling [ END of thread]

Administrator

In reply to this post by Grant Youngman

Ding! This thread has hit the list daily posting limit threshold for a
single topic. ;-)

Let's end this thread. If you wish to discuss the general topic of
cooling and direction of fan air flow, please take it to direct email.

73, Eric WA6HHQ
Elecraft list moderator.

P.S. The cooling on the K3's PA and fan air flow is very conservatively
designed and keeps it well below our design maximums.
====

On 4/6/2010 3:17 AM, Grant Youngman wrote:
> I suspect, like any good engineering team, they did it during design. I'd be really surprised if they just did it to verify if their design was any good :-)
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Joe Planisky

Re: K3 Cooling

In reply to this post by Rick Prather

This seems to be another one of those extremely variable things about
the K3. Some folk's rigs seem to be extremely quiet and others not so
much. The fans in my K3 are clearly audible at all speeds. At the
highest speed it competes well with the old tower PC I use for digital
modes. I've replaced the fans once with very little difference in noise.

Most (but not all) of the reports of very quiet fans I've heard of
were from rigs with low serial numbers. I suspect Elecraft may have
used different brands of fans at different times, which might account
for differences in reported noise.

As for how often they come on, from an idle temperature of 26C, it
takes about 1:15 of 20WPM CW at 50W into a dummy load for the fans in
my K3 to kick on.

73
--
Joe KB8AP

On Apr 6, 2010, at 7:43 AM, Rick Prather wrote:

> I dislike fan noise in my shack, one of the many reasons I love my
> iMac, and before I considered a K3 I made a trip to Aptos and they
> were kind enough to let me play with one for a bit including running
> the fans through their paces.
>
> Then, and now on my own K3, I find it nearly impossible to hear the
> first 3 speeds and the 4th speed is barely detectable. That, plus
> the fact the the fans rarely come on at any speed means the K3
> passes my personal "quiet test".
>
> Rick
> K6LE