General > General Technical Chat
US Ceiling Fan Efficiency Rule Proposal
<< < (7/13) > >>
NiHaoMike:

--- Quote from: coppice on September 04, 2023, 01:43:07 pm ---Really? There are huge numbers of BLDC motors which make considerable noise at quite low frequencies, presumably a beating sub-multiple of the switching frequency.

--- End quote ---
Harmonics from the square wave switching. The quiet fans like Noctua use sine waves for that reason.
Siwastaja:

--- Quote from: Zero999 on September 04, 2023, 01:30:36 pm ---
--- Quote from: Nominal Animal on September 04, 2023, 11:28:08 am ---
PC fans were always BLDC, with the PWM frequency between 21 kHz and 28 kHz (25 kHz typical).  RPMs vary between 300 and 3000, i.e. between 5 and 50 rotations per second (although smaller, 40mm fans as used in servers can be significantly faster – and horribly loud with a whiny sound spectra).

--- End quote ---
I've never seen a BLDC motor driven in that manner.  All the fans I've seen have a Hall effect sensor, connected to some transistors which emulate a mechanical commutator.

--- End quote ---

Higher-end PC fans have been using PWM for quite some time, and this is actually to reduce noise, namely torque ripple and the related low-frequency vibration and low-frequency noise (which, in case of small fans with high RPM, is not that low of frequency, but in several hundreds of Hz, is annoying to filter out, requiring soft mounting materials etc.) This is because in a simple hall-based, directly switched BLDC, a two-phase motor is out of optimal drive angle by +/- 45 degrees and three-phase motor by +/- 30 degrees. (It's just like if you had a clock which only had a hours hand and advanced one full hour click every hour, it would be off by +/- 30 minutes).

Using more sophisticated drive circuitry (FOC or something similar), you can add resolution into rotor position sensing (maybe just by interpolation), which allows you modulate the drive sinusoidally (or whatever happens to be the optimal wave shape based on motor design), creating torque vector which is always 90 degrees in advance compared to real physical rotor angle, producing smooth torque without ripple. The downside is that unless you build a linear amplifier (which would be quite crazy, and inefficient), you have to create the smoothly changing current levels by PWMing the motor windings, and you create a new noise problem. But it can be at higher frequencies, beyond the human's hearing.
Zero999:

--- Quote from: coppice on September 04, 2023, 01:43:07 pm ---
--- Quote from: Zero999 on September 04, 2023, 01:30:36 pm ---I can't say I've ever noticed any whine from a BLDC motor, even when I was much younger and could hear over 20kHz.

--- End quote ---
Really? There are huge numbers of BLDC motors which make considerable noise at quite low frequencies, presumably a beating sub-multiple of the switching frequency.

--- End quote ---
Yes, the noise predominately comes from the blades cutting through the air.


--- Quote from: Nominal Animal on September 04, 2023, 01:41:40 pm ---
--- Quote from: Zero999 on September 04, 2023, 01:30:36 pm ---I can't say I've ever noticed any whine from a BLDC motor, even when I was much younger and could hear over 20kHz.

--- End quote ---
Nevertheless, it is a well known phenomenon.  Microchip even made an appnote (AN771: Suppressing Acoustic Noise in PWM Fan Speed Control Systems) about it in 2002.  Feel free to ignore me (many do, and that's okay), but please do read that appnote to understand the issue I'm trying to bring up.  It affects slow high-current/high-load (large fan assembly) fans in particular, so therefore definitely does apply to BLDC ceiling fan motors also (or rather, their control circuitry, which is basically the only part manufacturers can cost-cut anymore, with just about everything else being basically standard).

--- End quote ---
I didn't know anyone in real life actually tried to control a BLDC motor in that manner. I've seen people talk about it here, but I haven't seen it in a commercial product. It's not very reliable because the motor driver has to keep restarting and it will draw large current spikes, due to the decoupling capacitors.

Variable speed fans inside computers and ventilation systems, have a separate PWM input, which is decoded internally by the motor driver and doesn't PWM the whole thing, so there's no noise.
coppice:

--- Quote from: Zero999 on September 04, 2023, 08:11:59 pm ---
--- Quote from: coppice on September 04, 2023, 01:43:07 pm ---
--- Quote from: Zero999 on September 04, 2023, 01:30:36 pm ---I can't say I've ever noticed any whine from a BLDC motor, even when I was much younger and could hear over 20kHz.

--- End quote ---
Really? There are huge numbers of BLDC motors which make considerable noise at quite low frequencies, presumably a beating sub-multiple of the switching frequency.

--- End quote ---
Yes, the noise predominately comes from the blades cutting through the air.

--- End quote ---
Please try to make sense. Reading comments before responding might help. Where did I mention blades? The subject was motors, not their specific use in fans.
Dacian:

--- Quote from: tszaboo on September 04, 2023, 12:33:38 pm ---TBH I saw a few American Youtuber do solar installation, and they always go with ridiculous numbers.
"I'm paying 10 cents a KWh and my monthly bill is 1500 USD" or something like that. And then they install a 100.000 dollar solar installation with enough batteries to run a small European city.
So yeah. You could use more regulations on the efficiency, especially on HVAC.

--- End quote ---

Is that a typo or is your monthly bill 1500USD ?At $0.1/kWh that means 15MWH per month.
Navigation
Message Index
Next page
Previous page
There was an error while thanking
Thanking...

Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod