Kx3 heatsink

PAE-Kx31 for the Elecraft™ KX3

PAE-Kx31 Heatsink for the Elecraft™ KX3                           (click for new window)

P/N: PAE-Kx31    Price: $89.90   

Shipping Status: Immediate, In Stock.

There are less expensive heatsinks available, but buying them is like buying a half-price ticket that only gets you half way to your destination!  The PAE-Kx31 gives the Elecraft™ KX3 up to 400% longer key-down transmit time than stock (band dependent) when cooled by natural convection. Hundreds of happy KX3 owners who have installed the best-performing and best-selling Kx31 now enjoy the extended transmit time at full power desired on digital modes. The Kx31 is a billet-aluminum piece black-anodized to match and compliment the appearance of the rig. It is designed for the majority of operators and will allow for greatly extended transmit time in any digital mode or band at full output. It incorporates several features not found on competing heatsinks:

  • Designed using thermal modeling software for best performance.
  • Ratio of base mass to fin area optimized for the duty cycle of digital modes.
  • Rounded cross-section for no-snag use in fabric cases, and no sharp corners to cut or damage adjacent objects.
  • When mounted on Elecraft™ KX3 along with GemsProducts™ SideKX plates and cover, the combo will fit in a standard Rose’s KX3 case.
  • Custom-color black anodized instead of powder-coated for superior thermal performance.
  • Radiusing compliments the design of the Elecraft™ KX3 and the GemsProducts™ SideKX.
  • Its design interlocks with and greatly enhances the impact resistance of the SideKX Cover.
  • Custom fin spacing matches KX3 screw placement for a clean appearance, unlike others it does not look like a stock heatsink profile modified to fit.
  • Low profile at each end for an interference-free fit with the PAE-Kx35 Mobile Mount (in beta testing).
  • Optimum compromise for most all operators between stock appearance and enhanced transmit time.
  • The Kx31 is supplied with correct longer replacement black-oxide stainless steel screws and a packet of heat-transfer grease.
  • The PAE-Kx31 offers nearly the maximum dissipation allowed by the footprint of the KX3’s top surface.
  • In addition the PAE-Kx31 offers the highest performance in the minimal volume as proven by multiple tests.
  • The PAE-Kx31 offers the best performance value of any aftermarket KX3 heatsink, delivering more cooling per $ than all others.
  • Each heatsink is visually checked after machining, and again after anodizing to make sure there are no defects before being shipped to you.

Size: 7.125″ x 1.5″ x 0.625″

Weight: 5.5 oz., 156 g.

Color: Custom dye batch black to match the Elecraft™ KX3

Thermal Resistance: <3°C/W

Surface Area: 38in²

Warranty: The Kx31 is warrantied against all manufacturing defects.  Read all Warranty details here.

Key-down Transmit Time Improvement:

160M-350%, 80M-300%, 40M-300%, 20M-250%, 15M-250%, 10M-350%, 6M-450%

Draft-free chamber KX3 PA Temperature vs. Key-Down Time Chart (click to view):

PAE-Kx31 chart

Key-down time, stock vs. Kx31 Heatsink                                (click for new window)

In order to validate the design, we ran a complete set of stock and modified performance tests. The test was conducted with a air tunnel around the KX3 to restrict the air movement to the convective flow powered by the heatsink itself. This removes room air movement as a variable, since almost undetectable amounts of movement can greatly increase the heat removed from a heatsink.

NOTE! (Please be wary of other ‘s claims that the same size or smaller heatsink can dissipate more heat than can the PAE-Kx31. Their claims are often the result of poor experimental design or outright guessing. We know of no other test done with a shield to eliminate external air movement, which can increase the cooling by 100% or more but is an uncontrolled variable. In most normal environments the PAE-Kx31 will allow much more transmit time than our own data supports.)

Also, the object of the tests was to validate the performance of the Kx31 heatsink, not evaluate the thermal conductivity of powder-coating, the thickness of which is largely an uncontrolled variable. To test the heat flow through the coating would mean the results would not necessarily be reproducible. To reduce this variable the case was prepped by removing the powder-coating from a 1″ x 2″ area around the PA transistor mounting holes, and heatsink compound was used between the transistors and case, as well as between the case and heatsink. We ran the KX3 RF output into a Bird Termaline 50Ω load, and measured RF power output with a Bird 43 with a 25H element. The DC power was provided by a Xantrex HPD 30-10 supply and was monitored using an HP 3468B DVM. 3 trials were averaged on each band pre and post-heatsink mod, and the summary data is posted below:

https://secureservercdn.net/198.71.233.52/t6o.048.myftpupload.com/wp-content/uploads/2014/03/PAE-Kx31-chart1.jpg

From the chart you can see that the improvement in key-down time is as much as 300-400% or more, depending on band. Our goals were to be able to run 10W in digital modes for extended periods on all bands without power fold-back, and to do as little harm to the excellent appearance of the KX3. This heatsink achieves both goals without any fans and without being excessively large (pictures on this site are of the last prototype run, and appearance is subject to improvement, please bear with me!).

PAE-Kx31 front view

Kx31 profile compliments SideKX cover and KX3                (click for new window)

We spent quite a bit of time modelling the thermal situation with the KX3. In the stock configuration the entire case back is an important part of the thermal equation, but it is not with an external heatsink. At 0.062″ thickness the thermal impedance of the sheet aluminum case back is relatively high compared to a dedicated heatsink on top. An important design factor for heatsinks cooled by natural convection is the surface area upon which the heat can transfer to air by contact. The fin-height to space ratio should not exceed ~2:1 or the velocity of air will be slowed by viscous shear friction. Radiative efficiency is important as well, but in a parallel-fin heatsink, much of the heat radiated by the fins is merely absorbed or reflected back by adjacent fins.

PAE-Kx31 top view

Kx31 custom fin pattern perfectly matches KX3 screw locations.                                     (click for new window)

The models show, and our testing with three different designs has borne out that over the footprint of the KX3 top utilizing normal convection, and regardless of fin design, the maximum amount of heat which can be consistently removed at room temperature is in the 6 watt range without hitting the 60°C PA temp limit. Beware claims by others that their designs can dissipate more than this. They have obviously not tested for pure natural convection. Consider the KX3 PA rejects 10-15 watts of heat or more (band dependent) while outputting 10W, and you will see that infinite key-down is not possible without a fan. Power-reduction due to hitting the 60° thermal fold-back is inevitable. Elecraft themselves never claimed the unit was 10W with all modes on all bands, so for those of you who have not looked, here is their PA specification:

“10 W PEP, 160-15 m; 8 W PEP, 12-6 m; 2 m (KX3-2M): 2+ W, 144-148 MHz.
Supply voltage of 11 V or higher (on key-down) required for settings above 5 W.
5 W or less recommended for high-duty-cycle modes (FM, AM, DATA). Power will
automatically be reduced if PA temperature or current limits are exceeded.”

( from KX3 Owners Manual Rev C2 (August 13, 2013), pg.52)

The KX3 PA designers hit an excellent compromise for 90% of KX3 owners. Considering the PA is broadbanded and consistently achieves low IM distortion performance the design is nothing short of amazing. However, many owners would like to have the full 10W available on all bands for extended digital mode transmit time. As many have found out, the stock PA thermal solution is less than optimum for extended transmit time at 10W, and for common digital mode usage, especially on the 10M and 6M bands where the limitation is worst.

The recent appearance of several dramatically different heatsink designs shows there is certainly a market for more than one compromise of improvement in transmit time vs. change in appearance. The N8WTT flat design works mainly by providing thermal mass, with a relatively small increase in radiating area (~15 sq.in. vs. stock 7.5 sq.in.), so after the initial heat-soak, the key-down time will begin to decrease with each transmit cycle. On the positive side, it makes a minimal change to the KX3 appearance. We would posit that there are some digital ops who need more heatsink than the flat heatsink can deliver. VE7FMN’s heatsink at ~36 sq.in. radiating area is another design which has its own set of compromises, but I’m sure it too will meet many KX3 owner’s requirements.

PAE-Kx31 side view5

Kx31 interlocks with SideKX Cover                                          (click for new window)

If you are a Side-KX cover owner you will enjoy enhanced protection from the cover when you mount the PAE-Kx31 heatsink. It interlocks with, and stiffens the top edge of the cover and gives additional protection from impact without making the cover more difficult to install or remove.

The design of the PAE-Kx31 is optimum for natural convection, and at 38sq.in, it affords more convective air contact area than others. For both its performance and appearance many hams will find the PAE-Kx31 to be the right choice.

Since originally designing and offering the PAE-Kx31, imitators have come on the market, copying features we pioneered like the SideKX cover reinforcing lip which also allows for more heat dissipating heatsink area. Why buy a heatsink from a company copying the original and best? The PAE-Kx31 incorporates more engineering than the competition, so get the highest-performance of any comparably sized heatsink: the PAE-Kx31.

1) What is the difference in thermal conductivity between the different materials used with heatsinks?

When evaluating a thermal path it is important to not confuse ‘Thermal Resistance’ and ‘Thermal Conductivity.’  As quantified in the table below, one is simply the reciprocal of the other:

Thermal resistance is expressed as the degree Celsius rise per Watt of applied heat over a square meter of the material.
Thermal conductivity is expressed as the amount of heat in Watts which is applied to a square meter of the material to raise it one degree Celsius.

Here is a table listing the thermal characteristics of different materials found in the path of heat flow of an Elecraft KX2/KX3:

From http://www.engineeringtoolbox.com/thermal-conductivity-d_429.html and
www.bergquistcompany.com

One conclusion you can draw from this chart: It is prudent to exclude air from the thermal path wherever possible due to it’s extremely high thermal resistance.  Let’s follow the heat as it is generated by the KX3’s PA FETs as it flows through the various surface interfaces to its release into the ambient environment:

  1. PA FETs to Case Inner Surface:  As delivered by the factory the PA FETs are mounted dry to the inside of the KX3 case, so it is advantageous to apply a thin film of thermal transfer paste between the two to bridge the gaps, displace air and increase thermal transfer.
  2. KX3 Case to Heatsink:  The outer surface of the case of the Elecraft KX3 has a textured powder coating.  Due to the flexibility of the thin aluminum case, over 95% of the heat will be transferred through a 1″ x 2″ (25 mm x 50 mm) area centered on the two PA FET attachment screws.  In this area a thin application of gap filling thermal transfer paste on the powder coating surface is advantageous.  It will help to displace the air trapped in the valleys of the textured powder coat as well as bridge the flexed thin aluminum case surface between and around the screws.  The transfer can optionally be enhanced further by removing the high thermal resistance powder coating to expose bare aluminum. In contrast to a KX3, a computer CPU and heatsink have their mating surfaces very flat and smooth and very importantly rigid to facilitate thermal transfer, however the KX3s case is many time more rough and flexible, so filling the resulting air pockets and gaps is advantageous.
  3. Heatsink to Air:  From the table above you can see that the thermal conductivity of an Type III (hard coat) anodize is as much as 800 times more than that of polyester powder coating, or 200 times more than a typical acrylic paint base resin.   This is the reason why, if a coating is required, anodizing is the surface treatment recognized industry-wide as the best way to finish a heatsink.  The other reason PAE employs a Type III hard coat anodize on our heatsinks is to render the heatsinks far more resistant to damage, since a Type III anodized surface has a hardness of 60-70 on the Rockwell C scale.

2) I have a new KX3 with the Elecraft Enhanced heatsink.  I’ve removed the screws but it is stuck on very tightly.  How do I remove it to install the Kx31?

The Elecraft Enhanced heatsink is held on by a piece of thermal transfer tape.  The adhesive characteristics of this tape rapidly diminish when heated.  The good news is that a regular hair dryer can provide enough heat to reduce the adhesion sufficiently to release it.  Thermal fold-back for the KX3 is set by Elecraft at 60°C, and a hair dryer outputs air at about 50-60°C (122-140°F).  This will release the adhesion with no chance of damaging the powder coating on the KX3.  Powder coating softens at around 100°C (212°F), and melts at around 150°C (302°F).   We installed one here on a test KX3 and after thermal cycling to 60°C six times then allowing 48 hours for the adhesion to cure at room temperature we indeed found the heatsink to be stuck. 

Elecraft Enhanced heatsink removal 40°C

Elecraft Enhanced heatsink removal @ 40°C

Simply heating it with a hair dryer to 40°C and pulling up on the bottom part of the “L” shaped heatsink with steady pressure was enough to allow it to be removed.  If you are using a hair dryer, the temperature may rise to 60°C.  This poses no potential damage to the KX3 and will make the tape that much easier to release.

There was no damage to the powder coating on the KX3, nor should there have been given the high melting point of powder coating.

Some of the new enhanced heatsinks may be stuck more firmly than ours, and will require persuasion.  While heating, A small flat-bladed screwdriver wedged between the case and the heatsink on one side will provide the necessary leverage to begin separating the two.

Note in the picture at left the thin white thermal transfer tape still partially hooked to both the KX3 and heatsink. 

3) Why don’t you offer a thermal pad for mounting the Kx31, I read they make the KX3 run 3° cooler?

The reality of the statement: “using a thermally conductive pad between the powder-coated case and the heatsink is 3°C better than without” is using the pad is better than no thermal interface material at all. Both options are inferior to the Option #3 outlined in the PAE-Kx31 manual, or even the Option #2. While an exact analysis would be both lengthy and obfuscating to most people, I will attempt to summarize the situation regarding the KX3 heatsinking options. First we must understand the relative thermal impedance of the materials involved. Thermal impedance is a material’s resistance to conducting heat. The chart below is expressed in in2°C/ W, or the temperature drop per square inch per watt of applied heat:

Thermal compound<0.1mil: 0.02
Polyester powder coating, 5mil: 1.5
Silicone thermal pads: 0.4
Air: 50

Analyzing the numbers given in the chart, you would correctly conclude that you do not want to be transferring heat through air. This is why the science of thermally interfacing two surfaces is the science of eliminating the air layer between them. If two surfaces were perfectly flat the air would be excluded and no additional interface aids would be required. As it is in reality, the surface textures only allow the peaks of each surface (called asperities) to touch and directly transfer heat. The thermal interface aids fill the voids between the asperities and are designed to be lower thermal impedance than the air they displace. With this in mind:

Option #3:
If you follow the installation option #3 in the PAE-Kx31 manual (removing the powder-coating directly around the PA FETs) , the heat only has to move from the PA FETs through 2in2of 0.063″ thick aluminum before it is inside the heatsink and being spread throughout the fins for convective removal. Keep in mind that using this method, much of the heat is transferred directly from the FET base to the aluminum case to the aluminum heatsink with very little interface thermal impedance, the thermal compound merely fills voids to enhance heat flow across them. This is why the very best application of the compound is very thin…translucent. You want it thin enough to flow away from the high-pressure areas and let the aluminum surfaces directly touch. The thermal compound is there only to fill the microscopic scratches where there is no direct contact, and the bottom of the PAE-Kx31 is extremely flat (<100uin RMS) to ensure good contact.

Option #2:
If you leave the powder coating on and spread some thermal compound on top of it as described in the PAE-Kx31 manual option #2, the compound will fill the voids, replacing air with thermal compound and enhancing the thermal transfer across the powder coat layer.

Thermal Pad Option:
In thermal interface engineering the thermal pads were developed to address moving heat between surfaces which were non-flat, as well as providing electrical isolation, and they can also lower the cost of assembly compared to thermal compound. They were not developed to have lower thermal impedance than thermal compound.
If you leave the powder coating on and use a thermal pad the heat must first move through powder coating and then through the thermal pads, the best of which are 5-10 times higher thermal impedance than thermal compound. The powder coating thermal impedance itself is 3x higher even than the pad. Regarding the idea that the pad allows the whole back of the heatsink to be in contact with the case: PAE’s recommendation in installation Option #3 is to remove the powder-coating from a 1″ x 2″ area on the KX3 case back directly surrounding the PA FETs. This results in 2in2 of area to directly transfer heat. For heat to move out of this area along the case back, it has a path which is only 0.062″ thick by 3″ long, so the heat moving sideways along the case away from this area must move through less than 0.2in2 of additional heat transfer area. The thermal impedance of this heat path is 10 times that of the 2in2 surface the PA FETs are mounted on, so less than 1/10th of the heat conducted directly THROUGH the case back moves ALONG the case back. This means the case back outside of that 1″ x 2″ area will not be substantially used to transfer heat to the heatsink.
Still, using a thermal pad will outperform dry mounting the heatsink because the pad is compliant and fills the voids in the powder coating textured surface.

Executive Summary:
Method #3 of removing the powder coating and directly mounting the heatsink with added thermal compound is much better than a big thermal pad in series with powder coating. Second best would be to use the heatsink grease directly on the powder coating and then mount the heatsink, which is the method #2 in the manual. Exactly how much worse the pad is than Option #2 or #3 depends on the flatness of the case and the exact pad used. If you just plain don’t want to get thermal compound on your KX3, use a thermal pad, but be warned, over time and pressure they can stick and discolor surfaces as well.

4) Why aren’t more fins better?

On the surface if it, this would seem to make sense, the more fins, the more area for heat to be conducted from the base of the heatsink. So it stands to reason if more fins are better, carried to it’s extreme a solid block conducts heat from it’s base the best of all, which is true! The problem with a solid block is it has little surface area for the surrounding air to touch and remove that heat, so we accept the need to have fins to increase surface area.

Although we are normalized to moving through it every day without noticing it, air is a viscous substance. The standard unit of viscosity is the centipoise, and water at 68.4°F (20.2°C) has a viscosity of 1.0 centipoise. Air at this temperature has a viscosity of 0.01983 centipoise, or roughly 2% that of water. It sticks to surfaces as well as water does, so air flowing between fins is similar to water flowing through a pipe. The smaller the space it is flowing through, the higher the resistance to flow. This is because the air molecules touching the surface of the heatsink are stationary on it, they are literally attached. They also strongly interact with the air molecules next to them. It takes work to pull the molecules apart, a function called viscous shear. This work is the resistance to air flow. The other main factor determining the optimum amount of fins is fin height. The deeper the channel the air is flowing through, the more difficult it is for the viscous air to move to the base of the fins, and the result is a diminishing advantage to additional height at some point as the air stagnates at the fin’s base.

In a heatsink designed for natural convection (no fan) the force moving the air is merely the difference in density between the air heated by contact with the heatsink fins and the cooler air below it. The heated air rises, pulling cooler air into place behind it. Heatsinks designed for use with fans can employ closer and longer fins, because there is a fan opposing the viscosity and forcing the air, but these heatsinks, like CPU and GPU heatsinks make poor natural convection heatsinks. Some claim they work well, but any legitimate testing would show otherwise.

The equation for optimum spacing and height of fins ends up settling out with ~2:1 fin height to space ratio being optimum. One way to make the heatsink more efficient is to increase it’s length along the fins. This is where the PAE-Kx31 was the first to employ a heatsink more than 1-1/4″ long front to back. The PAE-Kx31 heatsink is 1-1/2″ long, which allows an extra 20% more heat dissipation than our competitors. This extra length would interfere with the Gems Products™ SideKX Cover, so we innovated the unique lip in the heatsink which helps reinforce the cover. Since we first introduced this performance enhancing feature, our competition have copied it, which acknowledges the superiority of the original PAE design. The PAE-Kx31 has other design features which have not been copied, and which make it the highest-performance heatsink of it’s volume on the market.

5) What do the results displayed in the VE7FMN test report on Aftermarket KX3 Heatsinks mean?

We are glad to see people doing testing, even if the methodology is sometimes less than optimum compared to a NIST-conducted test program it is an occasion for everyone interested to learn. In the results table in the report, they tested four different heatsinks, our own PAE-Kx31 being one. The KB8UHN heatsink having much smaller surface area was substantially less efficient than the top three heatsinks. The results for the top three heatsinks were presented as a matrix of three runs at two power levels or 18 trials total. Of these eighteen trials, the results obtained were within the resolution of the instrumentation for sixteen of the trials. We did not see any control experiments to document the repeatability of the test setup, so there was no margin of error expressed associated with any of the results. This being the case, we can only overlay the resolution of the instrumentation involved, that being the PA temperature indication in the KX3 itself, which resolves to 1°C. Since resolution establishes the lower bounds of repeatability, the repeatability can be no better than 1°C. That the author was able to get results as repeatable as he was indicates careful attention to test conditions which is laudable! The temperature at test terminus was at 48°C for the CoolerKXPlus, and 49°C for the other two. The 1°C difference for the CoolerKX Plus represents a 4% difference, if it is actually repeatable.

This being established, the results confirm our own calculations and testing which we described when we released the PAE-Kx31 six months ago: in the footprint of the top of the KX3, at 25°C ambient and under natural convection, the practical limit of power dissipation is about 6 watts to a 35°C temperature differential. That three different heatsinks of varying proportions (the PAE-Kx31 being the smallest) performed virtually identically verifies this statement. In thermal modeling terms: the thermal resistance (expressed in °C/watt) of the top three heatsinks between the base and the air were all extremely close, and it is not a coincidence. Their performances are all close to the theoretical limit for a parallel finned heatsink with the footprint of the top of the KX3.

Interestingly enough, the test reported on the VE7FMN site was initially announced on August 5th as:

From: “Gary W. Hvizdak” <[email protected]>

Subject: [Elecraft] [KX3] What Your Dollar Actually Buys You — was “JT/heatsinks”

Date: August 5, 2014 5:28:40 AM MST

To: <[email protected]>

The author promised to “compare the various offerings based on the ratio of their performance versus their cost,” in other words which heatsink gave the best bang for the buck. Having optimized our design for performance vs. volume, we were looking forward to seeing the results of that comparison. We were somewhat disappointed when a test which just verified the footprint dissipation limit was performed and reported. We can overlay the test results on the initial test intent, which was to show the relative value of each heatsink. This is more relevant and informative to people wanting to decide which heatsink to purchase.

The total cost includes the cost of shipping and therefore has separate results relevant to hams in the USA and foreign hams. It shows the results of these calculations, giving the CoolerKXPlus the benefit of the doubt and using the results shows in Round3, the only one where any difference was noted:

Improvement in °C per $ spent.

Improvement in °C per $ spent.

We see now why they changed the testing goals. The fact that this test merely reveals the fact that heatsinks with the same footprint can only dissipate about the same amount of heat.  The KB8UHN heatsink, having much smaller surface area does not approach this maximum.

This test does reveal that PAE Kx31 design offers the best value per dollar of any available heatsink. Based on their metrics, to a US ham the PAE-Kx31 offers 38% more performance per dollar than the CoolerKXLite, 30% more than the CoolerKXPlus, and 24% more than the KB8UHN heatsinks. To a foreign ham, the PAE-Kx31 is an even better value, offering 63% more performance per dollar than the CoolerKXLite, 44% more than the CoolerKXPlus, and 63% more than the KB8UHN heatsinks. Our attention to proper design allows us to get the best performance in the smallest volume so the weight and size of the KX3 system would be minimally impacted. Still, the VE7FMN heatsinks are a fine piece of machining, and there is a difference in the ultimate performance between different heatsinks. Unfortunately the test they conducted does not fully reveal them.

As Don Wilhelm has pointed out, the design of a test as well as the exact instrumentation and controls determines the accuracy and repeatability of the results. In order to ensure reproducibility between testing labs, calibration standards must be checked and maintained. We applaud the testing just performed, but like many of you would like to see a more comprehensive series of tests to quantify the differences in performance.

Sours: https://proaudioeng.com/products/pae-kx31-heatsink-kit/

Does the KX3 really need a heatsink

It appears the answer is almost always no given the compromises and assumptions made by the engineers at Elecraft as Wayne Burdick (N6KR) reminds us…

“[. . .] supplemental heatsinking of the KX3 is *not* needed for typical digital-mode operation with the KX3. PSK31, RTTY, etc. will all function “out of the box” on the lower bands (20 meters is by far the most common band for digital communications).

If you want to use JT65 or other extremely narrowband modes, I do suggest doing extended VFO temperature compensation.”[1]

Trading heft for convenience the KX3 provides ample heat dissipation for the “usual” SSB or CW operating environment and cleverly implements a software frequency stability mechanism should incidental oscillator warming occur. By usual of course I mean a transmission duty cycle or power low enough for modest heat generation by those two small final transistors.

Digital folks push the envelope

For any assumption anyone can make about how customers will use products, some make their gear Go to Eleven. So it goes with the 100% duty cycle digital crowd. I’ve not personally done digital with my KX3 yet, but am listening carefully to the threads on the KX3 forums about restricting power to accommodate digital modes.

Modularity breeds solutions

Thankfully the Elecraft customer base is a rather useful pool of talent resulting in the creation of various aftermarket mods for the KX3. Such is the case with the SideKX panels and cover which I immediately purchased the very instant they came out.

The discussion of heatsinks stimulates quite a number of various new modifications for the KX3. W7GJ is one prototype pioneer concerning the use of JT65 and the KX3…

KX3 Heat Sinks for WSJT
and other Digital Modes

There are two themes regarding the KX3 and heat: Handling heat flow form the final transistors and managing the heat around the oscillator to improve frequency stability. The narrowband digital folks are wary of any frequency stability issues, but the KX3’s built in compensation system is a good step forward. Regardless, W7GJ deals with both the finals’ heat and oscillator stability with two distinct solutions.

All that said, it appears the handling of the final transistor heat load is the more popular issue to address. This stimulates an ever growing Elecraft KX3 heatsink cottage industry with many heatsink approaches coming on the market. Here is a short list, heaviest first…

The one that caught my eye is the PAE-Kx31 from Pro Audio Engineering…

Pro Audio Engineering PAE-Kx31
“Basic Elecraft KX3 Heatsink”

Thermal Engineering

What appeals to me most about the PAE-Kx31 is the amount of actual thermal engineering backing up the design decisions along with test results. This combined with the no-sharp-edge design made the purchase of this make and model a no brainer… if I really need a heatsink.

Does my KX3 really need a better heatsink?

Again I venture to say the folks at Elecraft know what they are doing about thermal management. That said, I have been designing electronics long enough to have “blown a few” components due to heat. One Altera EPLD actually cracked open and spit out flame. Needless to say, I didn’t read the fine print about thermal management on page 18 of the Altera datasheet. I fixed that with a revision to the design, but I have always been a bit sensitive to the topic ever since.

In another instance I satiated some JPL folks’ concerns about moving a hot regulator with heatsink from directly over VME cage fans to just 5 inches away. I conducted an experiment where I proved a fan one YARD away provided well over half the cooling capability. The slightest breeze pays big dividends, but fins make this much more effective.

So… I have faith my KX3 is just fine, but… “cooler is cooler.”

While I commend Elecraft for designing their KX3 RF circuit to use transistors with “grounded” tabs, halleluiah, I never really got past the idea of not using heatsink compound between those two final transistors and the base heatsink. Shudder!

I knew I would eventually put some compound on those finals, but the well thought out PAE model makes good sense. For me an improved heatsink made the cut. I ordered a PAE-Kx31.

Installation

The installation instructions suggest three options for installing the PAE-Kx31 heatsink. I chose option 2. There are a few web sites out there documenting the steps, including this excellent review by WN8U, so I won’t repeat that here. A couple points include…

  • Heatsink compound gets everywhere. Keep a paper towel handy and only use little pieces of it to mop up smears and then throw it away. If you don’t you’ll forget and wipe the stuff over something else.
  • Option 2 requires some dis-assembly of the KX3 bottom portion. When I re-assembled everything with the new heatsink in place, I noticed the two-pin antenna connector below the board… sigh. I had to remove the heatsink and other things to get it out. When I did, the heatsink screw at the antenna end jammed. I had to fix the threads with my 4-40 die.

Elecraft KX3 Heatsink modification – Worth it?

It is for me. I know enough about electronic design and reliability analysis that cooler components last longer. Even if I never run digital, the tests at Pro Audio Engineering reveal the superior heat flow keeping those finals as cool as possible with a passive heat management system.

The Elecraft KX3 is shown with the PAE-Kx31 heatsink along with the parts it replaces.

Snag resistant

In case anyone wonders… yes this still slides into my orange satchel by Rose’s covers with great ease. The round, snag-free, lines of the PAE-Kx31 pay big dividends here.

Conclusion

I believe the aftermarket PAE-Kx31 KX3 heatsink by Howard (WA4PSC) of Pro Audio Engineering achieves the proper balance of performance, size, shape and mass for those seeking high duty cycle digital modes or high reliability for all modes from their Elecraft KX3.

For the “every gram is sacred” minimal mass folks, the careful engineering of the PAE-KX31 offers, in my assessment, the best performance per gram of the models I examined.  I don’t have hard data on this assessment, however.

Howard accomplishes this with a round-edge, snag free design that won’t tear or rip your preferred KX3 carrier.

The heatsinks from the other manufacturers likely provide similar benefits so let your conscious be your guide.  Some of the larger and seemingly more massive models do seem to achieve “slightly better” thermal performance as suggested in this independent test[4]; The top three are close in performance and likely within the unreported margin of error.  Assuming the results of the top three are basically identical, one can assess performance vs. other variables.  Some have examined performance vs. cost.  I’m more interested in performance vs. mass. The PAE-Kx31 keeps pace with its heavier and larger counterparts while maintaining sleek proportions, rounded edges and unobtrusive appearance; The engineering optimizations are obvious.

I know the value of thermal modeling in my line of work and the PAE-KX31 hit the right buttons for me. Any of the top three in the independent test will greatly improve the thermal characteristics of your KX3.  Viva la choice!

References

  1. Elecraft Mail Reflector – KX3 and Digital Modes
  2. Lance Collister, W7GJ – KX3 Heat Sinks for WSJT and other Digital Modes
  3. Pro Audio Engineering – PAE-Kx31 Heatsink
  4. Aftermarket Upgrade Heatsink Alternatives for the Elecraft KX3 Transceiver, Adrian Ryan, 5B4AIY.
Categories RadiosTags Elecraft, heatsink, KX3Sours: https://www.hamradio.me/radios/elecraft-kx3-heatsink.html
  1. Spear awning
  2. Dorchester paws
  3. The archibald project
  4. Imdb jan hooks
  5. Loopnet houston

KX3 Heatsink (ProAudio Eng KX31 and KX32)

Description

My friend and partner on the KX2 Heatsink Howard Hoyte of Pro Audio Engineering has developed  a winning pair of  KX3 Heatsinks.  Below are the specifications on these proven products, but make sure to visit Howards web site for even more details and testing data!  

I currently DO NOT Stock this product, but here is a link to Howards web site where you can connect with him and place an order for these heatsinks along with his Power Supply!  

Shipping Status: In stock, immediate delivery.

KX31 version:      P/N PAE-KX31   Price: $89.00   ProAudio Web page for ordering here

There are less expensive heatsinks available, but buying them is like buying a half-price ticket that only gets you half way to your destination!  The PAE-Kx31 gives the Elecraft™ KX3 up to 400% longer key-down transmit time than stock (band dependent) when cooled by natural convection. Hundreds of happy KX3 owners who have installed the best-performing and best-selling Kx31 now enjoy the extended transmit time at full power desired on digital modes. The Kx31 is a billet-aluminum piece black-anodized to match and compliment the appearance of the rig. It is designed for the majority of operators and will allow for greatly extended transmit time in any digital mode or band at full output. It incorporates several features not found on competing heatsinks:

  • Designed using thermal modeling software for best performance.
  • Ratio of base mass to fin area optimized for the duty cycle of digital modes.
  • Rounded cross-section for no-snag use in fabric cases, and no sharp corners to cut or damage adjacent objects.
  • When mounted on Elecraft™ KX3 along with GemsProducts™ SideKX plates and cover, the combo will fit in a standard Rose’s KX3 case.
  • Custom-color black anodized instead of powder-coated for superior thermal performance.
  • Radiusing compliments the design of the Elecraft™ KX3 and the GemsProducts™ SideKX.
  • Its design interlocks with and greatly enhances the impact resistance of the SideKX Cover.
  • Custom fin spacing matches KX3 screw placement for a clean appearance, unlike others it does not look like a stock heatsink profile modified to fit.
  • Low profile at each end for an interference-free fit with the PAE-Kx35 Mobile Mount (in beta testing).
  • Optimum compromise for most all operators between stock appearance and enhanced transmit time.
  • The Kx31 is supplied with correct longer replacement black-oxide stainless steel screws and a packet of heat-transfer grease.
  • The PAE-Kx31 offers nearly the maximum dissipation allowed by the footprint of the KX3’s top surface.
  • In addition the PAE-Kx31 offers the highest performance in the minimal volume as proven by multiple tests.
  • The PAE-Kx31 offers the best performance value of any aftermarket KX3 heatsink, delivering more cooling per $ than all others.
  • Each heatsink is visually checked after machining, and again after anodizing to make sure there are no defects before being shipped to you.

 

KX32 Version    P/N: PAE-Kx32    Price: $99.90   ProAudio web page for ordering here

With the advent of increased 15W power output for the Elecraft™ KX3, more owners than ever are finding it difficult to keep their rigs cool.  We are proud to announce the release of the ultimate heatsink for the Elecraft™ KX3:  The Pro Audio Engineering Kx32!  Like its Kx31 brother, it is designed using thermal modeling and offers the maximum cooling by natural convection.  Only slightly larger than the Kx31, the Kx32’s performance exceeds the Kx31 by 25% or more depending on band. The Kx32 is a billet-aluminum piece black-anodized to match and compliment the appearance of the rig. It is designed for serious digital mode operators and will allow for greatly extended transmit time in any digital mode or band at full output.   The Kx32 incorporates several features not found on competing heatsinks:

  • Designed using thermal modeling software for best performance.
  • Ratio of base mass to fin area optimized for the duty cycle of digital modes.
  • Rounded cross-section for no-snag use in fabric cases, and no sharp corners to cut or damage adjacent objects.
  • When mounted on Elecraft™ KX3 along with GemsProducts™ SideKX plates and cover, the combo will fit in a standard Rose’s KX3 case.
  • Custom-color black anodized instead of powder-coated for superior thermal performance.
  • Radiusing compliments the design of the Elecraft™ KX3 and the GemsProducts™ SideKX.
  • Its design interlocks with and greatly enhances the impact resistance of the SideKX Cover.
  • Custom fin spacing matches KX3 screw placement for a clean appearance, unlike others it does not look like a stock heatsink profile modified to fit.
  • Optimum compromise for most all operators between stock appearance and enhanced transmit time.
  • The Kx32 is supplied with correct longer replacement black-oxide stainless steel screws and a packet of heat-transfer grease.
  • The Kx32 offers the maximum dissipation allowed by the footprint of the KX3’s top surface.
  • In addition the Kx32 offers the highest performance in the minimal volume as proven by multiple tests.
  • The Kx32 offers the best performance value of any aftermarket KX3 heatsink, delivering more cooling than all others.
  • Each heatsink is visually checked after machining, and again after anodizing to make sure there are no defects before being shipped to you.

Only logged in customers who have purchased this product may leave a review.

Sours: https://gemsproducts.com/product/kx3-heatsink-proaudio-eng-kx32/

Kx32 Heatsink for the Elecraft™ KX3                           (click for new window)

Kx32 perspective

P/N: PAE-Kx32    Price: $99.90   

Shipping Status: In stock, immediate delivery.

With the advent of increased 15W power output for the Elecraft™ KX3, more owners than ever are finding it difficult to keep their rigs cool.  We are proud to announce the release of the ultimate heatsink for the Elecraft™ KX3:  The Pro Audio Engineering Kx32!  Like its Kx31 brother, it is designed using thermal modeling and offers the maximum cooling by natural convection.  Only slightly larger than the Kx31, the Kx32’s performance exceeds the Kx31 by 25% or more depending on band. The Kx32 is a billet-aluminum piece black-anodized to match and compliment the appearance of the rig. It is designed for serious digital mode operators and will allow for greatly extended transmit time in any digital mode or band at full output.   The Kx32 incorporates several features not found on competing heatsinks:

  • Designed using thermal modeling software for best performance.
  • Ratio of base mass to fin area optimized for the duty cycle of digital modes.
  • Rounded cross-section for no-snag use in fabric cases, and no sharp corners to cut or damage adjacent objects.
  • When mounted on Elecraft™ KX3 along with GemsProducts™ SideKX plates and cover, the combo will fit in a standard Rose’s KX3 case.
  • Custom-color black anodized instead of powder-coated for superior thermal performance.
  • Radiusing compliments the design of the Elecraft™ KX3 and the GemsProducts™ SideKX.
  • Its design interlocks with and greatly enhances the impact resistance of the SideKX Cover.
  • Custom fin spacing matches KX3 screw placement for a clean appearance, unlike others it does not look like a stock heatsink profile modified to fit.
  • Optimum compromise for most all operators between stock appearance and enhanced transmit time.
  • The Kx32 is supplied with correct longer replacement black-oxide stainless steel screws and a packet of heat-transfer grease.
  • The Kx32 offers the maximum dissipation allowed by the footprint of the KX3’s top surface.
  • In addition the Kx32 offers the highest performance in the minimal volume as proven by multiple tests.
  • The Kx32 offers the best performance value of any aftermarket KX3 heatsink, delivering more cooling than all others.
  • Each heatsink is visually checked after machining, and again after anodizing to make sure there are no defects before being shipped to you.

Size: 7.125″ x 1.75″ x 0.750″

Weight: 7.2 oz., 204 g.

Color: Custom dye batch black to match the Elecraft™ KX3

Thermal Resistance: <2.75°C/W

Surface Area: 48in²

Warranty: The Kx32 is warrantied against all manufacturing defects.  Read all Warranty details here.

Key-down Transmit Time Improvement:

160M-430%, 80M-350%, 40M-350%, 20M-300%, 15M-300%, 10M-430%, 6M-550%

In order to validate the design, we ran a complete set of stock and modified performance tests. The test was conducted with a air tunnel around the KX3 to restrict the air movement to the convective flow powered by the heatsink itself. This removes room air movement as a variable, since almost undetectable amounts of movement can greatly increase the heat removed from a heatsink.

NOTE! (Please be wary of other ‘s claims that the same size or smaller heatsink can dissipate more heat than can the PAE-Kx32. Their claims are often the result of poor experimental design or outright guessing. We know of no other test done with a shield to eliminate external air movement, which can increase the cooling by 100% or more but is an uncontrolled variable. In most normal environments the PAE-Kx32 will allow much more transmit time than our own data supports.)

Also, the object of the tests was to validate the performance of the Kx32 heatsink, not evaluate the thermal conductivity of powder-coating, the thickness of which is largely an uncontrolled variable. To test the heat flow through the coating would mean the results would not necessarily be reproducible. To reduce this variable the case was prepped by removing the powder-coating from a 1″ x 2″ area around the PA transistor mounting holes, and heatsink compound was used between the transistors and case, as well as between the case and heatsink. We ran the KX3 RF output into a Bird Termaline 50Ω load, and measured RF power output with a Bird 43 with a 25H element. The DC power was provided by a Xantrex HPD 30-10 supply and was monitored using an HP 3468B DVM. 3 trials were averaged on each band pre and post-heatsink mod, and the summary data is posted below:

160M-430%, 80M-350%, 40M-350%, 20M-300%, 15M-300%, 10M-430%, 6M-550%

From the data above you can see that the improvement in key-down time is as much as 400-500% or more, depending on band. Our goals were to be able to run 12-15W in digital modes for extended periods on all bands without power fold-back, and to do as little harm as possible to the excellent appearance of the KX3. This heatsink achieves both goals without any fans and without being excessively large.

PAE-Kx31 front view

Kx31 profile compliments SideKX cover and KX3                (click for new window)

We spent quite a bit of time modelling the thermal situation with the KX3. In the stock configuration the entire case back is an important part of the thermal equation, but it is not with an external heatsink. At 0.062″ thickness the thermal impedance of the sheet aluminum case back is relatively high compared to a dedicated heatsink on top. An important design factor for heatsinks cooled by natural convection is the surface area upon which the heat can transfer to air by contact. The fin-height to space ratio should not exceed ~2:1 or the velocity of air will be slowed by viscous shear friction. Radiative efficiency is important as well, but in a parallel-fin heatsink, much of the heat radiated by the fins is merely absorbed or reflected back by adjacent fins.

PAE-Kx31 top view

Kx31 custom fin pattern perfectly matches KX3 screw locations.                                     (click for new window)

The models show, and our testing with three different designs has borne out that over the footprint of the KX3 top utilizing normal convection, and regardless of fin design, the maximum amount of heat which can be consistently removed at room temperature is in the 6 watt range without hitting the 60°C PA temp limit. In order to bypass this limitation we decided to extend the Kx32’s design an additional 1/4″ to the back of the rig to achieve additional fin area.  This plus an additional 1/8″ of fin height gives the Kx32 ~8w of natural convective dissipation.  The Kx32 extends past the case but does not interfere with the rig laying flat. Beware claims by others that their designs can dissipate more than this. They have obviously not tested for pure natural convection. Consider the KX3 PA rejects 10-15 watts of heat or more (band dependent) while outputting 10W, and you will see that infinite key-down is not possible without a fan.  With the advent of the 15W power limit on some bands the amount of heat rejected to the heatsink is even higher, potentially in the 15-20W range. Utilizing natural convection power-reduction due to hitting the 60° thermal fold-back is inevitable. Elecraft themselves never claimed the unit was 10W with all modes on all bands, so for those of you who have not looked, here is their PA specification:

“10 W PEP, 160-15 m; 8 W PEP, 12-6 m; 2 m (KX3-2M): 2+ W, 144-148 MHz.
Supply voltage of 11 V or higher (on key-down) required for settings above 5 W.
5 W or less recommended for high-duty-cycle modes (FM, AM, DATA). Power will
automatically be reduced if PA temperature or current limits are exceeded.”

( from KX3 Owners Manual Rev C2 (August 13, 2013), pg.52)

In addition, with the release of MCU firmware 3.68 Elecraft now states:

“- Up to 15 W power output (all modes) on 80-20 meters…Note on 15 W output level: This requires a power supply voltage of 12.8 V or higher on key-down as indicated by the KX3 itself (on the VFO B display). All of the usual firmware protections apply, i.e. the KX3 will roll power back to a lower level if necessary to keep current drain and temperature within a safe range, or if supply voltage is too low. 12 W max is the generally recommended level, so 15 W should be used only when really needed…”

( Elecraft announcement 12/28/2015)

The KX3 PA designers hit an excellent compromise for 90% of KX3 owners. Considering the PA is broadbanded and consistently achieves low IM distortion performance the design is nothing short of amazing. However, many owners would like to have the full 12W available on all bands for extended digital mode transmit time, and use the 15W available when desired.  As many have found out, the stock PA thermal solution is less than optimum for extended transmit time at 12W, and for common digital mode usage, especially on the 10M and 6M bands where the limitation is worst.

PAE-Kx31 side view5

Kx31 interlocks with SideKX Cover                                          (click for new window)

As with the smaller Kx31, if you are a Side-KX cover owner you will enjoy enhanced protection from the cover when you mount the PAE-Kx32 heatsink. It interlocks with, and stiffens the top edge of the cover and gives additional protection from impact without making the cover more difficult to install or remove.

Since originally designing and offering the PAE-Kx31, imitators have come on the market, copying features we pioneered like the SideKX cover reinforcing lip which also allows for more heat dissipating heatsink area. Why buy a heatsink from a company copying the original and best? The PAE-Kx32 incorporates more engineering than the competition, so get the highest-performance of any comparably sized heatsink: the PAE-Kx32.

1) What is the difference in thermal conductivity between the different materials used with heatsinks?

When evaluating a thermal path it is important to not confuse ‘Thermal Resistance’ and ‘Thermal Conductivity.’  As quantified in the table below, one is simply the reciprocal of the other:

Thermal resistance is expressed as the degree Celsius rise per Watt of applied heat over a square meter of the material.
Thermal conductivity is expressed as the amount of heat in Watts which is applied to a square meter of the material to raise it one degree Celsius.

Here is a table listing the thermal characteristics of different materials found in the path of heat flow of an Elecraft KX2/KX3:

From http://www.engineeringtoolbox.com/thermal-conductivity-d_429.html and
www.bergquistcompany.com

One conclusion you can draw from this chart: It is prudent to exclude air from the thermal path wherever possible due to it’s extremely high thermal resistance.  Let’s follow the heat as it is generated by the KX3’s PA FETs as it flows through the various surface interfaces to its release into the ambient environment:

  1. PA FETs to Case Inner Surface:  As delivered by the factory the PA FETs are mounted dry to the inside of the KX3 case, so it is advantageous to apply a thin film of thermal transfer paste between the two to bridge the gaps, displace air and increase thermal transfer.
  2. KX3 Case to Heatsink:  The outer surface of the case of the Elecraft KX3 has a textured powder coating.  Due to the flexibility of the thin aluminum case, over 95% of the heat will be transferred through a 1″ x 2″ (25 mm x 50 mm) area centered on the two PA FET attachment screws.  In this area a thin application of gap filling thermal transfer paste on the powder coating surface is advantageous.  It will help to displace the air trapped in the valleys of the textured powder coat as well as bridge the flexed thin aluminum case surface between and around the screws.  The transfer can optionally be enhanced further by removing the high thermal resistance powder coating to expose bare aluminum. In contrast to a KX3, a computer CPU and heatsink have their mating surfaces very flat and smooth and very importantly rigid to facilitate thermal transfer, however the KX3s case is many time more rough and flexible, so filling the resulting air pockets and gaps is advantageous.
  3. Heatsink to Air:  From the table above you can see that the thermal conductivity of an Type III (hard coat) anodize is as much as 800 times more than that of polyester powder coating, or 200 times more than a typical acrylic paint base resin.   This is the reason why, if a coating is required, anodizing is the surface treatment recognized industry-wide as the best way to finish a heatsink.  The other reason PAE employs a Type III hard coat anodize on our heatsinks is to render the heatsinks far more resistant to damage, since a Type III anodized surface has a hardness of 60-70 on the Rockwell C scale.

2) I have a new KX3 with the stock Elecraft enhanced heatsink.  I’ve removed the screws but it is stuck on very tightly.  How do I remove it to install the Kx32

The Elecraft Enhanced heatsink is held on by a piece of thermal transfer film.  The adhesive characteristics of this tape rapidly diminish when heated.  The good news is that a regular hair dryer can provide enough heat to reduce the adhesion sufficiently to release it.  Thermal fold-back for the KX3 is set by Elecraft at 60°C, and a hair dryer outputs air at about 50-60°C (122-140°F).  This will release the adhesion with no chance of damaging the powder coating on the KX3.  Powder coating softens at around 100°C (212°F), and melts at around 150°C (302°F).   We installed one here on a test KX3 and after thermal cycling to 60°C six times then allowing 48 hours for the adhesion to cure at room temperature we indeed found the heatsink to be stuck. 

Elecraft Enhanced heatsink removal 40°C

Elecraft Enhanced heatsink removal @ 40°C

Simply heating it with a hair dryer to 40°C and pulling up on the bottom part of the “L” shaped heatsink with steady pressure was enough to allow it to be removed.  If you are using a hair dryer, the temperature may rise to 60°C.  This poses no potential damage to the KX3 and will make the tape that much easier to release.

There was no damage to the powder coating on the KX3, nor should there have been given the high melting point of powder coating.

Some of the new enhanced heatsinks may be stuck more firmly than ours, and will require persuasion.  While heating, A flat-bladed screwdriver wedged between the case and the heatsink on one side will provide the necessary leverage to begin separating the two.

Note in the picture at left the thin white thermal transfer tape still partially hooked to both the KX3 and heatsink. 

3) Why don’t you offer a thermal pad for mounting the Kx32, I read they make the KX3 run 3° cooler?

The reality of the statement: “using a thermally conductive pad between the powder-coated case and the heatsink is 3°C cooler” is that using the pad is better than no thermal interface material at all. Both options are inferior to the Option #3 outlined in the PAE-Kx31 manual, or even the Option #2. While an exact analysis would be both lengthy and obfuscating to most people, I will attempt to summarize the situation regarding the KX3 heatsinking options. First we must understand the relative thermal impedance of the materials involved. Thermal impedance is a material’s resistance to conducting heat. The chart below is expressed in in2°C/ W, or the temperature drop per square inch per watt of applied heat:

Thermal compound<0.1mil: 0.02
Polyester powder coating, 5mil: 1.5
Silicone thermal pads: 0.4
Air: 50

Analyzing the numbers given in the chart, you would correctly conclude that you do not want to be transferring heat through air. This is why the science of thermally interfacing two surfaces is the science of eliminating the air layer between them. If two surfaces were perfectly flat the air would be excluded and no additional interface aids would be required. As it is in reality, the surface textures only allow the peaks of each surface (called asperities) to touch and directly transfer heat. The thermal interface aids fill the voids between the asperities and are designed to be lower thermal impedance than the air they displace. With this in mind:

Option #3:
If you follow the installation option #3 in the PAE-Kx31 manual (removing the powder-coating directly around the PA FETs) , the heat only has to move from the PA FETs through 2in2of 0.063″ thick aluminum before it is inside the heatsink and being spread throughout the fins for convective removal. Keep in mind that using this method, much of the heat is transferred directly from the FET base to the aluminum case to the aluminum heatsink with very little interface thermal impedance, the thermal compound merely fills voids to enhance heat flow across them. This is why the very best application of the compound is very thin…translucent. You want it thin enough to flow away from the high-pressure areas and let the aluminum surfaces directly touch. The thermal compound is there only to fill the microscopic scratches where there is no direct contact, and the bottom of the PAE-Kx31 is extremely flat (<100uin RMS) to ensure good contact.

Option #2:
If you leave the powder coating on and spread some thermal compound on top of it as described in the PAE-Kx31 manual option #2, the compound will fill the voids, replacing air with thermal compound and enhancing the thermal transfer across the powder coat layer.

Thermal Pad Option:
In thermal interface engineering the thermal pads were developed to address moving heat between surfaces which were non-flat, as well as providing electrical isolation, and they can also lower the cost of assembly compared to thermal compound. They were not developed to have lower thermal impedance than thermal compound.
If you leave the powder coating on and use a thermal pad the heat must first move through powder coating and then through the thermal pads, the best of which are 5-10 times higher thermal impedance than thermal compound. The powder coating thermal impedance itself is 3x higher even than the pad. Regarding the idea that the pad allows the whole back of the heatsink to be in contact with the case: PAE’s recommendation in installation Option #3 is to remove the powder-coating from a 1″ x 2″ area on the KX3 case back directly surrounding the PA FETs. This results in 2in2 of area to directly transfer heat. For heat to move out of this area along the case back, it has a path which is only 0.062″ thick by 3″ long, so the heat moving sideways along the case away from this area must move through less than 0.2in2 of additional heat transfer area. The thermal impedance of this heat path is 10 times that of the 2in2 surface the PA FETs are mounted on, so less than 1/10th of the heat conducted directly THROUGH the case back moves ALONG the case back. This means the case back outside of that 1″ x 2″ area will not be substantially used to transfer heat to the heatsink.
Still, using a thermal pad will outperform dry mounting the heatsink because the pad is compliant and fills the voids in the powder coating textured surface.

Executive Summary:
Method #3 of removing the powder coating and directly mounting the heatsink with added thermal compound is much better than a big thermal pad in series with powder coating. Second best would be to use the heatsink grease directly on the powder coating and then mount the heatsink, which is the method #2 in the manual. Exactly how much worse the pad is than Option #2 or #3 depends on the flatness of the case and the exact pad used. If you just plain don’t want to get thermal compound on your KX3, use a thermal pad, but be warned, over time and pressure they can stick and discolor surfaces as well.

4) Why aren’t more fins better?

On the surface if it, this would seem to make sense, the more fins, the more area for heat to be conducted from the base of the heatsink. So it stands to reason if more fins are better, carried to it’s extreme a solid block conducts heat from it’s base the best of all, which is true! The problem with a solid block is it has little surface area for the surrounding air to touch and remove that heat, so we accept the need to have fins to increase surface area.

Although we are normalized to moving through it every day without noticing it, air is a viscous substance. The standard unit of viscosity is the centipoise, and water at 68.4°F (20.2°C) has a viscosity of 1.0 centipoise. Air at this temperature has a viscosity of 0.01983 centipoise, or roughly 2% that of water. It sticks to surfaces as well as water does, so air flowing between fins is similar to water flowing through a pipe. The smaller the space it is flowing through, the higher the resistance to flow. This is because the air molecules touching the surface of the heatsink are stationary on it, they are literally attached. They also strongly interact with the air molecules next to them. It takes work to pull the molecules apart, a function called viscous shear. This work is the resistance to air flow. The other main factor determining the optimum amount of fins is fin height. The deeper the channel the air is flowing through, the more difficult it is for the viscous air to move to the base of the fins, and the result is a diminishing advantage to additional height at some point as the air stagnates at the fin’s base.

In a heatsink designed for natural convection (no fan) the force moving the air is merely the difference in density between the air heated by contact with the heatsink fins and the cooler air below it. The heated air rises, pulling cooler air into place behind it. Heatsinks designed for use with fans can employ closer and longer fins, because there is a fan opposing the viscosity and forcing the air, but these heatsinks, like CPU and GPU heatsinks make poor natural convection heatsinks. Some claim they work well, but any legitimate testing would show otherwise.

The equation for optimum spacing and height of fins ends up settling out with ~2:1 fin height to space ratio being optimum. One way to make the heatsink more efficient is to increase it’s length along the fins. This is where the PAE-Kx32 is the first to employ a heatsink more than 1-1/4″ long front to back. The PAE-Kx32 heatsink is 1-3/4″ long, which allows an extra 50% more heat dissipation than our competitors. This extra length would interfere with the Gems Products™ SideKX Cover, so we innovated the unique lip in the heatsink which helps reinforce the cover. Since we first introduced this performance enhancing feature, our competition have copied it, which acknowledges the superiority of the original PAE design. The PAE-Kx32 has other design features which have not been copied, and which make it the highest-performance heatsink of it’s volume on the market.

Sours: https://proaudioeng.com/pae-kx32-ultimate-heatsink-kit-elecraft-kx3/

Heatsink kx3

WINDCAMP Heatsink Shield Kits+Cover case for ELECRAFT KX3 Transceiver ham Black (Black)

KX3 shield kit , total external radiator , with a handle left ,right side plates ,Canvas bag shields and other five components . The left / right side plate, a radiator are aluminum alloy material, the CNC precision machining, surface do black (or red) sand surface oxidation treatment, compared to KX3 the original host shell surface dusting treatment has better wear resistance, durability and texture. Handle about projection of the effective protection panel of the button, knob, covered with protective cover is convenient to pack and carry

Packing include:
LEFT-SIDE PLATE*1PC
RIGHT-SIDE PLATE*1PC
RED EXTERNAL RADIATOR*1PC
PROTECTIVE COVER*1PC
CANVAS BAG*1PC
Note :
1/Products are external radiator, with a handle on the left panel and right side plates, shields does not contain the ELECRAFT KX3
2/that this suite contains no screws, still use the KX3 assembly of the original screw.

Sours: https://www.amazon.com/WINDCAMP-Heatsink-Shield-ELECRAFT-Transceiver/dp/B015X7FJ6O

Hi everyone,

I mainly do QSOs in digital modes. Mainly PSK31 and JT65. Recently I’m also using WSPR to test my setup efficiencies.
Each of those modes (as most of the digital modes) work by pushing all power for a certain amount of time, usually about 1 or 2 minutes. Even working with “only” 5 Watts, the internal temperature of the KX3 quickly rises, and when it goes to 60° C tha KX3 stops working full power.

Also, even most important, as the temperature rises the VFO tends to drift. For most of the digital modes, drifting too much, means no decoding on the other side.

It is crucial to keep temperatures as low as stable as possible.

Recently a few people decided to build heatsink add ons for the KX3. All very well done, an most very good looking to perfectly suit the KX3 look.

The main problem is that they are not cheap… they all cost around $100 + shipment.

Being a “maker” (I like to build things myself) and thanks to my experience with PC modding, I decided to go with a cheap and effective solution that is also not ugly.

I bought 5 graphic CPU heatsink 35×35 mm (14 mm high)

heatsink

and some thermal adhesive tape (by Akasa 80×80 mm)

akasa

I dismantled the “heatsink” bar of the KX3 and took all the paint out with sandpaper on both sides. The attached the 5 square heatsinks with the thermal tape to the Elecraft heatsink bar.

Part list

The thermal tape is this one:
http://www.amazon.com/Akasa-ak-tt12-80-Thermal-Adhesive-Tape/dp/B001GIM9V8

You just need one of this thermal tape. It is 8x8cm and it’s enough to cover the heatsink surface.

While the heatsink are those one:
http://www.ebay.com/itm/35x35x14mm-High-Quality-Aluminum-Green-Heat-Sink-For-Electronic-Computer-H80-/200922118534
or
http://www.ebay.com/itm/35x35x14mm-High-Quality-Aluminum-Green-Heat-Sink-For-Electronic-Computer-H80-/181110944574

You need 5 of them.

 

Total cost less than 30 Euros and 20 minutes of work.

Here are a few images of what it looks like.

IMG_20140710_083321
IMG_20140710_083222

It’s like my KX3 now has hairs 😀

Anyway, the important is that tests say that performances are very close (if not better) of most of the “commercial” solution. With 5W it never goes above 45°C.

If you want something “professional” go for the commercial solutions, you won’t regret it. But if you are low on budget and/or like to do things yourself then this is a nice and working option 😉

72/73, Andrea IU4APC

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