VOVANE Electric Dust Blower, 150000RPM Air Duster Compressed Air Spray, 3-Speed Super Power Cordless Air Duster, Mini Blower Battery for PC Cleaning Kit, Keyboard, Car, Sofa (WHL #121)
This is puzzling.
Around two months ago, I bought one of these electric (cordless) air dusters. I do technically own some pressurized air equipment (14l tank, 12V pump and manual pump), but it’s always bulky and inconvenient to use. Since battery technology has advanced so much over the last couple of years…some nifty dude invented the server fan on a 18650. And aside from actually filling things up with a defined pressure, that’s basically good enough for most tasks that mainly consist of “dusting things off” needs.
I bought this on Amazon Germany instead of Aliexpress, for a multitude of reasons – number one being that the items on Ali were priced basically the same (strange!), number two being that I needed to order something from Amazon anyway (and they have this 40€ minimum order value nowadays for free shipping), number three was that the BS claims on Amazon were comparable to those “add some zeroes” seller dudes on Ali. I paid 29.99€, this included the unit, some charge cable and some gimmicky cleaning utensils, of which I have used exactly zero to this date, but they might come in handy some day. Original seller photo, since I cannot be arsed to take a photo of all these:
The unit itself is actually decent – of course it’s not the category 5 hurricane at your disposal that they’d like to claim, but the air flow and pressure is impressive for such a tiny device. The magnetic nozzle is holding on for dear life at full blast and jets away on the slightest contact, so I put some tape around, there’s no need to ever take it off (and it does improve the air stream significantly).
There’s three speed settings that can be adjusted with the round button on the back (also the ON switch), and the trigger-style button on the front activates the fan. The lower settings also sometimes stay on and need to be stopped with a second button press, while the top setting only stays on while pressed, but that’s a minor thing.
Item description from Amazon:
Strong electric dust blower: this air duster with 150,000 rpm motor speed immediately generates strong air flows that penetrate crevices and corners to thoroughly remove dust, chips and stubborn dirt. With 140g of wind pressure, it blows away dust from hidden areas such as keyboard cap crevices, camera keyhole slots, car vents, etc. – even tiny particles won’t go unnoticed.
Rechargeable and energy-saving: This dust blower has a long-lasting lithium-ion battery. Once charged, it can be used several times, so you no longer have to buy costly disposable air cans and save money in the long term. It has three adjustable ventilation modes that allow you to accurately adjust the wind strength according to your cleaning needs. This improves cleaning efficiency while contributing to energy savings.
Long-lasting battery and fast charging: the mini blower has a 5000 mAh high capacity lithium-ion battery, with which deep cleaning of several devices are easily implemented. With Type-C fast charging, charging efficiency improves significantly – fully charged in just 2.5 hours. Supports various chargers such as laptop, power bank, car charger, etc., so you can charge the battery at any time in the office, on the go in the car or during outdoor work.
Versatile application and simplicity: this dust blower battery is an all-rounder: it gently cleans gaps in keyboards, cameras and car seats without residue. It allows air mattresses/pool floats to inflate quickly, cleans picnic residual waste/floors and removes flea hair. With strong wind, it blows leaves/cobwebs away time-saving. After car washing, it dries crevices/wheels of water/mud. Whether for electronics, outdoors or at home – whether in the home, car or outdoors.
Portable and lightweight: this mini blower only 220 g and can be easily held with one hand – perfect for transport. Made of heat-resistant and shock-resistant ABS material and equipped with a non-slip grip sole, it allows safe use. Whether camping, clearing leaves in the garden, or spontaneous cleaning tasks at home, it’s always at hand and combines efficiency with portability.
Does it work (a very niche question in this post, I know): Yes, indeed. These pictures are from the third (!) round of dusting through bedroom and hallway, which are generally clean on the floor due to Helene Wischer, but this thing bursts out dust bunnies from below and behind furniture, and releases noticeable amounts of loose dust from e.g. the top of doors, rough walls (I got an outdoorsy kind of scratch coat in the bedroom), and of course, radiators. Charge it up, put it to full speed, hold your breath and get crackin. And fuck off and close the door behind you before taking the next breath…15 minutes later, that stuff sits around everywhere, again and again:
Now for the puzzling bit: The banner spec of 150000 RPM is most likely bullshit – and if I can prove that, Amazon might feel the need for a rebate, a full refund, or some other kind of goodie to make up for it. Same goes for the battery, which has a claimed capacity of 5Ah. Let’s do that first, that should be easy.
Well, the battery claims are actually true, charging this thing from empty to full after the video below used 25084mWh and 4773mAh (likely a little juice left, since this was the express discharge). Probably no DC-DC inside, but even that is so close to claimed 5000mAh specs that there’s no point in attacking it that way. 13 hours later, an additional 216mWh and 43mAh fit into the battery, so the self-discharge at absolutely peak 100% SoC isn’t THAT bad. I also haven’t had the feeling that vampire drain in general is a thing, it holds up well. Charging time 0->100% also only slightly exceeded the 3.5h claimed charge time (3.7 to 3.8ish hours, I didn’t check every minute), but it gets noticeably warm during the first two hours, and it could be faster in general.
Funnily enough, the sticker on the device itself only claims 2500mAh, so we’re far beyond that in any case, and maximum current draw is “only” 1.4A instead of the claimed 1.5A, that’s perfectly fine. Those 1.4A are still kept when 1 of the three status LEDs stops blinking during charge, and it drops to like 0.9A when two LEDs are static and only the last one blinks as charge indicator.
Then there’s the runtime claim: 13 minutes on full blast, and much more on the lower settings. Not only is the 13 minute claim quickest to check, it’s also the best one to test battery performance, since impedance will directly impact runtime. The slow test is only checking for total capacity and will likely not be affected by peak current degradation. To be clear: Both could be faked with gradually slower speeds (like over the years, not over the single test run, that would be easy to spot) if the air duster is tracking battery health – but I very much doubt it does.
So…I ran it on full blast. While it almost moved itself when I tried laying it down, the initial superspeed is quickly turned down to a very steady pace. Total runtime: Start at 0:25, sudden stop at 18:55, so that is 18 minutes and 30 seconds of runtime at maximum speed, very well inside the claimed specification again.
But what about those 150000 RPM? That’s the difficult bit.
I did extract the dominant frequency of that run with a little bit of ChatGPT-assisted python code and LOTS of RAM:
The rapidly dropping top line matches the listening experience pretty well, so I would assume this is directly proportional to RPM. I, however, do not know the scaling factor, and there has to be a factor, since 16500ish Hz translates to literally a million RPM. Is it 13, since the rotor has 13 blades? That’s still 75kRPM, which is FAR beyond everything that I have ever pulled out of a server chassis. Sure, the fan is only a 30mm one, and they typically come in 8 to 15kRPM flavours…but 75k? From a super generic gadget for 30 bucks (so cheaper than most high-end server fans) that also has a battery and case? Not convinced.
Next idea: The fan has three blue LEDs in front, for whatever reason. On low speed, I can tell from peripheral vision that those aren’t static, they do blink with several hundreds of Hertz. What if they’re actually tied to rotation, maybe one LED per motor phase? Let’s check, I got an old photo diode BPW34 that is specified up into the MHz region, and an oscilloscope.
That’s almost 21 cycles in 50ms, so somewhere in the 400 to 420Hz region, for the duster running on low speed. That’s in the ballpark of 24500RPM with no scaling factor, which again would match with the 27000RPM banner spec…but 24500RPM? On a cheapo plastic fan from a cheapo cordless gadget?
Checking this against another waterfall plot from some audio of the fan:
The dominant frequency with the little wobble at the start matches the fan (and its spin-up phase) nicely, it even got the little speed variations that are clearly audible: (there also is a line at half frequency, just not as strong, especially not at the very beginning – that’s the factor of two that will be too much in the next line)
Let’s say 10800Hz average and again scaling factor 1/13 due to 13 blades…that’s 830Hz or 49800RPM. That’s unrealistic again, but super close to x2 of the previously guessed 24500RPM via the LEDs. So they are coupled to rotational speed, I just need to figure out the correct scaling factor!
Different tool: Flashlight. Using the Triple XM-L2 from WHL #74 (which still is missing a comparison shot, I know…). That one is PWM-dimmed, also clearly visible to me, so I got to use it at full brightness only. PWM frequency apparently 330 Hz. Quick sanity check:
Super low intensity
Roughly half:
And full brightness, with the PWM gone as it runs on 100% duty cycle:
Sooo…if I shine light through the fan, and the fan LEDs point the other way and are so super dim compared to the flashlight at full blast anyway…shouldn’t the rotor-stator strobe effect be visible as well? Here we go, please ignore the readings of the Rigol, those are trash in this instance, we got 10.5ish cycles across the 2ms full span, or 5300Hz:
Again, given 13 blades (and I can move the photo diode very close to the fan, so that we only have strobes from one static piece of the fan), that is 405Hz or 24500 RPM.
Dangit. Reflections? Some other effect with the static air guide in there? I’d say the signal is very clear, but let’s try a more narrow beam…get the laser out!
Digged up some cheapo Dealextreme (?) laser pointer in green, since the blue 405nm version that I found first is so ungodly bright with the same barely half full batteries…
Sanity check again: CW laser, no PWM shenanigans: (AC coupling, in case you expect a voltage here)
Laser shining through the fan, it doesn’t get much more focused than this:
Almost 11 cycles in the same 2ms window, so let’s say 5400Hz this time, divide that by 13 is 415Hz or 24900RPM.
That still matches all the other results, but I cannot believe this is the real RPM.
…the fuck am I missing?
Bonus image: Medium speed setting, fan LED, 49 to 50 cycles over the span of 50ms. That is basically one kHz or 60000 RPM. What’s the advertised speed of that setting? 62000RPM. Fuck me!
