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KX2: testing two different cooling techniques

NOTES ON THERMAL TESTING of KX2: Two configurations tested: (a) aluminum heat sink, thermally coupled with heat sink paste, held in place with bungee cords; (b) pair of small 12 vdc fans (blowing onto rig), current draw 170 mA. Details: 10m cw; 10w; calling “cq sota cq sota cq sota de k7zoo k7zoo k” 20 wpm with 10 sec repeat time; ambient air temp 38-40 C; freshly charged stock batteries used for each test; no wind; no sun. RESULTS: The heatsink cooled about 1.5 deg C, while the fans cooled just over 6 deg C. PERSONAL CONCLUSIONS: (1) heatsinking is – in general – less effective than blowing air; (2) keep the rig in the shade; (3) keep the rig in the wind; (4) use 5 watts if possible; (5) transmit duty cycle for this test exceeded my normal operating style. (6) most of my activations use only 1 amp-hour, so the fans (at 170 mA) are actually a viable solution. de K7ZOO

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Last year I noticed while operating my KX2 it was getting crazy hot. I tried the shade, wind thing which as times could not achieve both at the sametime. I ended up going with that heat sink now sold by Gem products. It works but pricey but seems to work well. So far (knock on wood) I have not seen any high temps from it.


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Malen – I am hoping that someone with a commercial solution (such as the GEMS SideKX product) could reproduce the test conditions as a comparison. It would be informative to know how many degrees of cooling are achieved by this product. I should add that the ambient temp here in Tucson was about 38-40 deg C.

Excellent start, Curt. An integrated fan / heat sink combo will be better still. On my company’s laser beam dump products, which had large area-per-weight heat sinks, adding a fan doubled the rated allowable power for the same delta T, if memory serves. Paul, K9PM, and I have been discussing this issue for awhile. Another low tech solution is to use some circuit freeze (spray is -60F) in an aerosol can (some cans are only 4 ounces) to drop the heat sink to just cold-to-the-touch temps every few minutes. Good project! As we say in the antenna business, a measurement is worth many expert opinions!
Best, Ken

Hi Ken, thanks for the feedback. Pretty much any use of a heatsink would require either diving back into the innards of the KX2, or using heatsink paste. Both of these activities, from my perspective, are not attractive, so while there might be some thermal advantage I’d prefer to use only a fan. Very interesting and informative would be similar measurements of a commercially available solution.

Curt, did you see KH2SR’s little fan he posted over on the KX2 FB page last week? Looks interesting.

Thanks for the test info…

73, Todd KH2TJ

Hi Todd,

No, I didn’t use a fan with an associated heatsink. That approach looks very convenient, merely using adhesive to attach the fan. However, I wanted a removable solution.

I purchased a couple of stand-alone fans from a local electronics store. Using an adhesive I combined the two fans into one assembly. I will be designing a fixture to hold both fans next to the rig, also holding a stock KX2 battery pack, and have it 3D printed. This is certainly not a simple approach, but I enjoy designing widgets.

These data confirm my experiences on numerous summits: a lack of wind is a key contributor to the rig overheating.