Electronic – What properties vary with the number of blades on a BLDC fan

Here's some examples:

• M0802512 -- "Life Time: On-going testing"
• Sunon Maglev -- N/A (two sources)

In comparison to these non-magnetic bearing statistics:

• Sintec sleeve: 45'000h @ 20^oC; 15'000h @ 60^oC
• Superflo: 50'000h @ 40^oC
• Ball: 70'000h @ 40^oC; 40'000h @ 25^oC
• HydroWave: 50'000h @ 40^oC
  _{Note: 1 year = 8766 hours.}

Looks like traditional bearing MTTF wins! My point is that at the moment this technology is marketing fluff, regardless of its merits. Real MTTF numbers will tell the story... not that these are real numbers: take them with a grain of salt, as they are subject to lawyer jibbajabba and marketing hype. ^{(And no, that doesn't mean manufacturers have to wait 70'000h+ to characterize MTTF -- it is characterized much earlier using techniques to speed up the working hours.)}

EDIT: Thanks to fuggetaboudit, I did some more research, and the pinout, I'd guess, is:

Black = GND

Red = +12V

Yellow = Trip-Point Alarm (see option -04 in the document)

Green = PWM (option -06 in the document)

The document I'm referring to is here. In it, it says a suffix of -09 means:

PWM speed control circuit (option -06 or -56) terminated in a third lead wire (standard = blue) and an open-collector, non-latching, low-pass/high-fail, trip-point alarm circuit (option -04 or -54) terminated in a fourth lead wire (standard = yellow).

Given that your yellow wire acts like an open-collector output and your green wire controls the fan speed depending on an applied voltage, I'd bet this is the correct pinout.

Somewhat relevant: http://www.nidecamerica.com/apps_pwm.htm

I would be very certain that Mark is correct:

Black = GND

Red = +12V

Yellow = Tach Trip-Point Alarm (After checking the Nidec Datasheet)

Green = PWM

Every Nidec fan I've encountered has followed this color scheme, and most common 4-wire PWM fans in desktop computers also use the same color scheme. Empirical evidence, but given your measurements, I'd be willing to bet they're correct.

If you have access to a signal generator, try generating a 25kHz, square-wave, 0-5V signal to the green wire, and seeing how the duty cycle of that signal affects the fan speed.