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Axial Fan Parameters

Just got a stack of surplus fans for the heatsinks I’ll probably use in the disinsector: Cofan FP925HH12B. Either these are really old or there’s a typo in the model number printed on the fan label. I’d expect it to be …9225… to indicate a 92 mm frame x 25 mm thickness. It’s close enough to get to their specs page.

Cofan axial fan

Cofan axial fan

They draw 370 mA (rated 450 mA) in free air = 4.4 W. The “HH” designation means “Super High Speed” and wow are they noisy despite their 37.6 dbA spec. Fortunately, that won’t matter inside a closed box.

The label is downstream, which means the hub and bare blades are upstream. They’ll be under the shelves, so I think I can get away without guards.

The model number breakdown says that they have a “protection chip” which seems to be the thing that produces the status output. That output (yellow wire) is a square wave with a frequency twice the fan’s actual speed: 107 Hz → 6420 cycles / min → 3210 RPM. The open collector output requires a pullup resistor to +5 V. It take a while to spin up the fan enough to get a decent output waveform; don’t sample the status for maybe a second after power-on.

Putting a fan on that crude air flow straightener produces about 3.2 m/s across the exit end, which works out to 10.5 ft/s = 630 ft/min. There’s a distinct flow dent near the middle of the air column, so I suspect the baffles are too far upstream for this fan.

Making a number of barely justifiable assumptions, the output is around 1.4 m3/min = 50 ft3/min, which is close enough to the rated free air output of 1.8 m3/min = 64 ft3/min.

They will start and run at 5 V (below the 8 V minimum rating), draw 110 mA, spin at 1470 RPM, and push 1.1 m/s. For whatever that’s worth.

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