Mark AJ6CU released a fan shroud for the “tall” Sunil case a short while back. See https://www.thingiverse.com/thing:3790450
He was curious to check out its effectiveness, against just using the supplied heat sinks or using the heat sinks with a fan. So here are the results….
- ubitx v4 with stock PA transistors and the new larger heat sinks being shipped with the case
- Noctua 1800RPM 80mm 12V fan (Blowing in)
- Little Volt/Temp gauge that was mounted on the front panel (measurements in Fahrenheit)
Search for: ” DROK Car Voltage Temperature Display” on amazon if you want one!
Unfortunately Mark took the “shroud measurements” on a different day than the”no shroud measurements”. So focus on the temperature gain over “ambient temperature, for a true comparison.
The first set of tests were for 5 minutes on 40m into a dummy load.
The second set was on FT8 CQ into a dummy load, until the FT8 watchdog timer terminated transmissions.
No Shroud Ambient After 5 Min Xmit Temp Gain
Fan Off 81F 128F +47
Fan On 76F 94F +18
With Shroud Ambient After 5 Min Xmit Temp Gain
Fan Off 83F 128F +45
Fan On 81F 98F +17
Operating for 5 minutes into a dummy load suggest that a fan is probably as good as a fan and a shroud.
On FT8 CQ (into Dummy load, until the watchdog kicked TX off):
WITH Shroud Ambient After 5 Min Xmit Temp Gain
Fan Off 84F 105F +21
Fan On 82F 88F +6
Of course the missing measurement is the FT8 CQ with just a Fan. Mark thought of this test *after* he had put everything back together. 🙁 .
Mark AJ6CU has made a 3D template for a fan cowling for your µBITx. The 3D template for the fan shroud can be found on thingiverse here:
It basically bolts onto the 80mm fan at the rear of the case (you might recognize the “tan” of a Noctua fan — much quieter than the one supplied). It sits on the uBitx motherboard with two slots straddling the heat sinks.
Marks notes that he has not powered on his µBITx yet, but suspects it will keep things nice and cool even in digital modes. This was designed with Fusion 360. There have been several other suggestions for adding ducts for cooling some of the hotter spots in our radios.
I was inspired in this effort by the work by another cooling shroud for the “shorter” of Sunil’s cases. See:
It is better to have a quiet fan that meets all of the requirements without any extra circuitry that can fail. You can make a fan more quiet by adding a series resistor. Experiment to find the right value, but perhaps start with around 500 – 1000 ohms.
Another easy solution is to simply run the fan from the 12V transmit power, assuming that is not what you are already doing. No reason to run the fan while receiving.
If a noisy fan is the only choice, then putting in a controller to minimize the noise while still removing the heat is the next best solution. If properly designed, installed, and tuned, then there would not be a change in the amount of heat that can be removed as the heat sinks get hotter. The response time can get in the way of keeping the finals cool quick enough to not cause an issue. An always on at max fan does not have this issue.
Woody KZ4AK suggests fan controllers are easy to build and minimize noise when not needed.
Arvo KD9XLC has put one of these 12v fans that cost less than a dollar on the back of his Excelway case from Bangood (which apparently now on sale for $8.88).
You could attach the fan to the cabinet with hot glue, or use the correctly sized bolts/nuts.
And if you don’t want those fans to run on receive connect them to the TX 12v line, namely at pin 3 on U2, which is what Arvo did.