Discussion in 'Hardware' started by LennyRhys, 22 Apr 2020.
Damn man... that really blows (sorry, couldn't resist)!
But if you flip it round and look at it from the other side, it sucks too!
I'm trying to plan as far ahead as possible for fan testing, making sure I have bits and pieces at the ready to make all the measurements less time-consuming. I made this on the fly yesterday evening, and it will allow me to test the power of any of my fans with a DMM accurate to 10mA. I have a second (el cheapo) DMM on order so I can measure voltage and current simultaneously.
I saw a guy on Youtube use his smartphone as a sound level meter... if I was ever to go down the route of measuring fan noise, I'd get a dedicated meter.
A thought I just had, if you're curious you could post them down to me and I could image them with our thermal camera, as I'd be curious how hot they're getting when they run!
Probably not even warm - I'm guessing not much above room temp for most PC fans. Will definitely keep it in mind for when all my testing is done.
Most fans arent 50W however
Being stupid and doing something stupid, always sucks but, as Marge Simpson said, "Stupid is, as stupid does."
Idiots always blame someone else for their own inadequacy, as they don't understand how it can be their own fault.
Its more that a fan blows and sucks.......
Infrared Thermometers are reasonably cheap on eBay. I've got a couple of them and both are accurate to around 2ºC
They're severely limited by the material though. I have access to some fairly expensive Thermal imaging cameras, so could easily image them which would give great thermals
The sound level meter was just delivered by UPS - that's impressive, all things considered.
I now have the equipment to measure the following values:
PWM duty cycle from 0-100%
Speed (laser tachometer)
It's gonna take some time to set up a suitable test "station" but I'll do some provisional testing as soon as I get a chance.
Here's a wee "family shoot" of some of the gear for testing. I put a new 9v battery in the Tenma and it works like a dream.
Here's a quick test with my 3,400rpm Delta AFB fan (25mm version). Nominal power is 600mA.
in free air: 3,430rpm, 510mA
on the box: 3,030rpm, 610mA (inrush current 1.1A... yowza - don't plug this one into your mobo)
From 1m away, I'm measuring 54dBA (max.) with the fan running in free air. This is compared to the spec sheet stat of 49.5 (max.) in an anechoic chamber, so it's not bad. If I measure the SPL when the fan is on the box, it jumps to 63dBA.
A high-speed fan like this which develops a lot of pressure will obviously see a more pronounced increase in power draw than "standard" PC fans, but the negative correlation between speed and power is interesting nevertheless.
I also did a quick SPL test with the Gentle Typhoon. I notice that Nidec measure from 25cm and then subtract 12dB, and they measure 42dBA... I get 42.5dBA from beside the fan and 46dBA in front. I'm pretty sure the fan manufacturers measure from the side, and this seems like a good way for me to standardise my testing of fans (rather than doing it at 1m). I should really re-test the Delta above this way, but I'm tired and it's 10pm!
I'm pretty excited to test various fans when equipped with filter / grating or when on a rad or heatsink. I think I'll probably draw the same conclusions as other testers who find that two fans with the same or similar sound level may not have the same sound quality... and at that point it becomes a matter of preference.
You're not messing about - fair play
There are some interesting correlations around fans and their properties. I have to admit I deal mainly with centrifugal fans and blowers (Roots, Screws), but I believe the physics transpose. Please understand there is a bit of simplification going on here
I'm considering 'free running' to be pretty much a design condition for the fan and the start point.
Essentially, a blanked output (i.e. dead head) is the highest pressure/load condition of a fan. The dense air will slow the fan as there is more resistance over the blade area. Also usually the noisiest - due to the high air pressure.
A blanked input on the other hand will reduce the air pressure around the fan blades. Maintaining this depression will increase the load on the fan, but not by as much as dead head. This will usually cause the fan to speed up slightly due to the thinner air around the blades.
Interestingly the size of chamber you use will also have an affect - mainly on the time taken to reach these conditions, but also the overall noise level. A bigger chamber takes longer to fill, a smaller chamber the reverse. Like loud speakers, the size/shape of the chamber will also affect the acoustic properties (I'm unsure of the acoustic properties from a fan that is totally dead head using a flat plate vs a chamber)
I suspect with the size chamber you are using, and the calibre of the fans, reaching the condition isn't going to take long. You may well find that different size chambers affect the level and spectrum of the noise produced.
I popped back through the thread to have a look at your chamber - I couldn’t remember if you had a damper fitted. Fitting a damper with the same or larger free area than your fan would allow you to vary the load on a fan. You could even have it fully open to test blanking the input, which may help you with results on filter testing (You could flip the fan - but who doesn't like a damper?)
Nice work on the test gear - appreciate that a lot
@cobalt6700 Nice observations - I think it's essential to simplify things because the complexity of what's going on at a molecular level is quite something. For those who don't know, in just one cubic centimetre of air there are around 5.3x10^18 oxygen molecules, or 5,300,000,000,000,000,000, which makes up a little over 20% of the volume. The rest will be Nitrogen, Argon, Methane, Hydrogen and so on. The aperture of a standard 120x25 square fan has approximately 220cm^3 of volume (not including the motor hub), and if you multiply both numbers together and then again by the average air velocity in metres/sec or feet/sec, you will get the total number of molecules passing through the fan every second.
Back OT, you're right about the chamber effectively amplifying the sound, and it will be different for each fan depending on the fan's resonant frequency (or frequencies). You mention a damper, and I'm assuming you mean some sort of exit valve to allow air to pass through the chamber at varying rates, right? This would be really interesting as it would be a way of establishing some sort of PQ curve for the fans.
I've been reading how the manufacturers do their axial fan testing using a double chamber, and they have an auxiliary blower mounted at the "output" which allows them to create a zero static pressure condition within the chamber for measuring maximum airflow.
@LennyRhys Cheers - no problems. Fluid mechanics are indeed a complex thing!
Sorry - yeah I am refering to an exit valve - damper is what we call them in industry. Yep, spot on. It could be something as simple as a sliding plate/plates or hinged door/doors. Indeed - you would be able to pretty much repoduce a fan curve.
Ah, yeah that makes sense. Sounds like you're building youself quite the setup with an adjustable damper and an aux blower
Probably won't bother with an auxiliary blower as for my testing it would be sufficient to have maybe 1/2 to 2/3 of the air exiting the chamber. In that scenario it would be a good approximation of a high impedance heat sink or grill, and it will give me an entirely new set of parameters for comparing the best-performing fans. Will be doing it this afternoon and hope to make a short video of the "finished" setup with a little demonstration!
I'm going to use a 54mm hole cutter, and two such holes will give me approx half of the surface area of a fan aperture, which is perfect.
Say hello to my little friend!
@LennyRhys that's fair enough
The reason I suggested an apature larger than the fan area is down to the relationship between airflow and pressure and it not being linear Having 1/2 the area of the fan for the exit aperture wont eqaute to 1/2 the fan flow, it will be slightly less due to the restriction and increase in pressure the fan has to deal with. I'm unsure as to how much in your application without doing the maths. That said, any adjustable opening is going to allow you to get a better set of results.
Airflow through fins is a whole thing in itself. Due to the thin, long apatures, velocity and the induced eddy currents are the main factors affecting airflow pressure (which as we know, is why fans should 'push' through a finstack). I have no idea on the restriction/pressure drop values of types of air coolers. This is different again for mesh's, where surface area reduction is the main factor.
Having the full sized opening would allow you to mount a cooler on the back, you could then meaure the resistance with your rig
I hope you take my comments as friendly - you seem to know what you're talking about and don't want to come across as patronising
Very much looking forward to a video demo later
No problem at all - all your insights are extremely valuable as you're the one with the knowledge and I'm the hobbyist! I'm learning more as I go, and I'm realising why fluid dynamics is a discipline in itself... it's crazy.
I didn't realise that the relationship between area and airflow was non-linear, however as you say any type of exit for the airflow will allow me to measure the static pressure below maximum, which is much more meaningful when comparing actual / real-world performance. I'm suspicious that with the dampers open, I'll struggle to measure any pressure at all because it will be <1mmH2O with most low rpm "silent" type fans. I don't really want to do thermal tests, because introducing a test system just makes the number of variables go through the roof... at least with my current setup, the variables are kept to a minimum and are relatively easy to control.
Here's what I did, and I'm going to paint up the box to finish it off. The doors are 2mm sheet styrene with a pretty tight fit and should be substantial enough to stop any airflow in the closed position. I also re-mounted the front of the box because the previous solution wasn't durable.
Cool That;s good to hear. I love learning new stuff too, and as for fluid dynamics.... yeah. Fluids do some mad things!
So pretty much all airflow relationships are non-linear. As you can see on the datasheet for the G1238B12BBZP-00, most of the graphs are curves or 'wiggles'. The only one that is fairly linear is the 'with filter installed'. AFAIK this a result of the depression created directly infront of the fan and the affects on the blades. We very rarely do this in industry, so, not 100% on that one.
As for dampers open - you may well be right for the low rpm fans you have. I do however think you are going to discover some interesting relationships .
For thermal tests I guess you were refering to me suggesting a heatsink - I was intending to suggest measuring PQ with heatsink
Nice dampers! I see you have left space underneath them too
Some quick maths: Force = Pressure / Area, so with your G1238B at full tilt the enclosure would be subject to an internal pressure of 51mmH20, or 500Pa. 1 pascal is 0.102Kg/m2, which means the Nidec is exerting 50.98Kg/m2. Your 54mm hole cutter has created an opening of 0.0023m2, which means each damper will have 117g pusing it out. (This is slightly incorrect, as as the damper lifits off slightly the pressure will be applied over more of the surface area of the damper - I'm guessing these are 65mm*95mm, which would equate to around 300g)
I would say that 2mm styrene will cope with 300g, lets see how the glue gets on
Good guess - the dampers are 70x105, and they are held firmly against the MDF by the rails so it takes a fair bit of force to slide them. I did think I might need to seal the edges with something but the max static pressure reading with my AFC is spot on at 15mmH2O so it's worked out really well, which is great.
I was mentioning thermal tests as a way to obtain performance numbers when the manometer is effectively out of range, e.g. with sub-1,000rpm fans.
Anyway here's a quick and scrappy video just to show the setup in action with one of my AFC1212DE Deltas. The static pressure at the lowest speed (around 1,200rpm) is pretty much bang on 1mmH2O. I bumped the duty cycle just a little to show the jump in static pressure, and you can see the pressure drop by about half a mil on the scale when I open one of the dampers.
With a little more time (and preparation) I'll get a proper video put together as there's a lot to cover!
Separate names with a comma.