Important: updated assembly guide (v1.1) for the aluminum enclosure
There is an updated assembly guide (version 1.1) for those of you who have purchased the new aluminum enclosure. Corrections to the parts list, clearer photos and an important note about removing one of the two pieces of sticky tape attached to the fan. Special thanks to Dave, PJ4VHF, from Bonaire for discovering the issue.
I have on my "short list" of things to do to re-lubricate one of the noisiest of the lot (which happens to be on my ham shack) them with PTFE oil (which lasts much longer than the terrible stuff typically used by the manufacturer) to see if this helps: If it does, I'll have to reconsider what to do about the fans - and when - as that would not bode well for longevity.
Having powered down my Kiwi for a week or so due to other work in my shack, I powered it up again a while back, hearing it "shudder" as it tried to spin up. In the past, I've noted that this can often happen with a cold fan with an "Oilite" (sintered bronze) bushing that is dry. These sorts of "bearings" are very common in inexpensive fans, but they have a few weaknesses, including:
- The oil used in cheap Chinese fans seems to "dry out" rather quickly. It seems that the volatiles slowly evaporate, leaving behind heavier fractions. (I've noticed that it often smells slightly of naptha - not usually a sign of quality...)
- Oilite, by its nature, often tends to be "dry" when cold: Warming up, the embedded lubricant will often come to the surface, but this may take a while.
- If it goes on too long, the bearing surfaces can become worn and/or "coked" (e.g. surface lubricant may be cooked to a sludge/solid from friction) and reduce the ability of the embedded lubricant within the oilite to surface - if there's even any left.
* * *
Over the past 15 years, in non-critical applications (and because I may not have had a new fan of the same size - or because I was cheap...) I've actually "fixed" sleeve-bearing fans just to see what would happen over time. Sometimes this "fix" was simply re-lubricating it, but other times it required disassembly and cleaning with denatured alcohol to remove gum from the "dried" oil, reassembling and re-lubricating. In particularly tough cases, I would heat up the oilite bushing with a soldering iron before applying the new lubricant to help work it into the pores.
Unless the sleeve bearing or spindle shaft was physically damaged (due to galling, perhaps) the "rebuilt" fan has lasted far longer than the time before the fan had failed - and almost none of these have failed since. Some of these re-lubed sleeve fans have out-lasted ball-bearing fans, which often have lubricant that is of no better quality than is found in the sleeve bearings and offers little benefit in longer life: Typically, when this happens to ball-bearing fans, they cannot be fixed because the balls/races have been damaged/spalled from running dry.
* * *
Such seems to be the case of many of these very inexpensive fans, including the fan that comes with the Kiwi case: Insufficient/poor quality oil that evaporates quickly (within a year or so) resulting in noisy operation.
Carefully peeling the sticker back, I put a few small drops of a PTFE (Teflon) based synthetic lubricant - the same that I have used to "fix" fans in the past (as well as "un-gall" potentiometer shafts on an audio amplifier at my work about 20 years ago - none of which have "re-galled" since). This stuff is sold in the U.S. as "Super Lube" (made by Synco) which is a liquid in a bottle or a small pen-sized dropper - readily available on Amazon.
After working the new lubricant into the bushing (sliding it back and forth to distribute it) I cleaned the plastic housing with a cotton swab and alcohol and covered it with a round piece of plastic tape (the reason for cleaning the plastic) to keep dust out of it. (Note that "Household oil" or "3-in-1 oil" should not even be considered for this purpose - and is probably similar to what was originally used. Don't even think of something like WD-40!)
Since it was re-done, the fan's noise has been only a slight whine of the fan's BLDC driver and air movement - it wasn't this quiet when it was new.
I have three more Kiwis at a remote site, all of which are getting noisier every time that I go there, and they will all get the same treatment on the next site visit and will be observed in the long term.
I found unsticking the fan from the PCB and sticking it instead to the side and bottom of the case stopped all the noise. Only slight air movement noise now.
I just received my KiwiSDR Enclosure, and I have noted two things: It appears to have been made for the version of KiwiSDR that uses the Beaglebone Green. I have a Beaglebone Black, and notice the front plate of the enclosure in the area marked "USB Host" collides with the power connector of the Black.I suppose I can mill that out. Also, no connection for the fan on the Black. Again, I can cut the connector and wire it to the board in some manner. The fan is marked as 5 Volt, but the directions indicate it is connected to a 3.3 Volt supply. Since I am wiring the fan myself, any suggestions about using 5 Volts or 3.3 Volts for the fan? Thanks,
The enclosure was designed for the BeagleBone + Kiwi kit which is indeed the green. It can be used without the end plate so why not try it first and cut the plate later?
The fan is run at 3.3V, as the air movement does not require full speed and that should give less fan noise and longer life.
On the BBG the fan is run at 3.3V. But it's a 5V fan and will run fine at that voltage (not as quiet of course).