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I have a project involving a 200mm 12VDC PC cooling fan (FS-200RB) that will be used for cooling me - not a computer.

The fan is labeled: 12V DC / 0.42A / 5.04W

With a source of 12V, it is not moving enough air for my taste.
I don't need the fan to last a long time, it will only need maybe 20hrs of use for my project, but I'd of course prefer to avoid destroying it.

With 12V applied, I measured the current in-line to only be about 0.13A. And if I hold the blades to stall it, the current only rises to 0.18A.
With 15V applied, and the current was 0.17A full speed, 0.22A stalled.

I want to overvolt this fan even more, but I'm not sure where to draw the line. I could continue raising the voltage past 15V, but I don't know how quickly it can be expected to fail.

I'm also not sure why the current would be so much lower than the 0.42A rating. Is this common for DC motors? Is 0.42A only for the instant it starts up? Stalling it doesn't even reach near that much current. This makes me feel like the fan is not reaching its normal potential, let alone an "unsafe" potential.

Why would the fan be using such little current and how can I theoretically/numerically determine an over-voltage limit?

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    \$\begingroup\$ Unless this is an expensive fan, buy two and sacrifice one to the gods of pragmatic engineering. Then back off by 20% in the other one... \$\endgroup\$ – Brian Drummond Mar 7 '16 at 10:53
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Stall current probably does not do what you think it does b/c most fans are stall protected. This means that they limit current when the motor is stalled and won't actually apply the full current.

The upper limit on overvolting depends almost entirely on the components selected and the architecture of the circuit. If you have 20V MOSFETs, they will probably function reasonably well at 15V (although that is too close for comfort for me). If you don't know, then I wouldn't go any further.

Depending on the architecture, there may also be a linear voltage regulator involved. If this is the case, then you would be placing a higher thermal load on the regulator and coming closer to failure here as well.

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  • \$\begingroup\$ Could you guess as to why the fan was using nowhere near the stated "0.42A"? \$\endgroup\$ – Bort Aug 5 '16 at 13:00
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    \$\begingroup\$ There are lots of potential reasons, but a couple of guesses. 1. The manufacturer had to put a number on it that would be true over all of productions units - say 1million fans. That 'o.42A' should cover a lot of fans and still be 'in-spec'. 2. Aerodynamic - different fan blades draw different torque/speed from the motor based on the fan curve (pressure vs. flow) and you might not be at a high power point. Most axial fans are most efficient at or near 'free air', or at very low pressure. 3. The manufacturer is taking startup current into account in their labeling. \$\endgroup\$ – slightlynybbled Aug 5 '16 at 23:02

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