I have built a 3D printer from parts. It is using a standard 12V power supply, an Arduino Mega 2560 replica and a RAMPS 1.4 board. The hotend cooling fan is connected to the 12V-AUX pin (the one right next to the x axis stepper driver) on the RAMPS board so that it continuously receives power as long as the machine is turned on. The printer is controlled by the Marlin firmware.

When I give power to the board, the cooling fan starts spinning with a lot of noise. It sounds like it is receiving a higher amount of current than it should. Moreover, the noise is not steady, but fluctuates slightly. After about 30 seconds, it gets slightly quieter; after about 40-50 seconds, there is a sudden break. From then on, the fan spins quietly and regularly.

According to measurements with a multimeter, the power supply is keeping a constant and correct voltage of slightly over 12V right from the beginning. Hence, I suspect the issue is somewhere on the RAMPS board.

I am worried about this being more than a problem of unpleasant noisiness. What could be the cause and is there more to worry about?

You can listen to a recording of the sound: 3D printer hotend cooling fan noise

Note that I am not talking about a fan for cooling the extruded plastic, but the one sitting on the extruder heatsink.

Shutting down the printer (even literally unplugging the power supply) and plugging it back in does not lead to the startup noise appearing again. Only when waiting for multiple minutes before reconnecting does it happen again.

The voltage to the fan is measured to be constant. The current, on the other hand, correlates with the sounds heard. It starts at 110 - 115 mA. When the fan is quiet, it is at about 90 mA.

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    $\begingroup$ After the fan has stabilized; if you power cycle the printer, will it then start all over again with the high speed? Something tells me this could be a software / control system thing, and that the first few seconds is just the software adapting to the situation. $\endgroup$ – Tormod Haugene Jul 16 '18 at 11:56
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    $\begingroup$ Note: this is not a PWM fan. (thanks to @Oscar for mentioning this. Answer deleted) $\endgroup$ – OyaMist Jul 17 '18 at 21:43
  • $\begingroup$ @TormodHaugene I edited the question to add some more details. $\endgroup$ – meyfa Jul 19 '18 at 9:39
  • $\begingroup$ @OyaMistAeroponics You are right, it isn't a PWM fan. The 12V should go straight from the power supply to the board and from there to the fan. $\endgroup$ – meyfa Jul 19 '18 at 9:39
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    $\begingroup$ I have had similar experience, but that was for the part cooling fan which is controlled over PWM, so in that respect it is different from your problem. Can you measure the voltage of the fan during startup with a multimeter and report back? This is not a simple problem; possibly be caused e.g. by a faulty voltage regulator? $\endgroup$ – 0scar Jul 19 '18 at 9:43

Now that you have done some measurements, you could make some conclusions.

The voltage over the fan is reported to be constant, but the current starts at 110-115 mA and reduces to 90 mA over time.

With limited knowledge of electronics you can conclude that the resistance of the fan is not constant as the resistance determines the amount of current through the fan. So the fan resistance increases over time. This could just be a manufacturing problem or characteristics of the fan. You could try to replace the fan with another fan to see if this fixes your problem.

  • $\begingroup$ Please excuse the super late reply. Yes, this is it. A fan from a different brand does not have the same issue. I guess I learned that if there's a problem with the fan, then the first place to look for a solution might be that very fan... Duh. Thanks for your patience! $\endgroup$ – meyfa Aug 15 '18 at 22:11
  • $\begingroup$ The discussion about resistance is a bit misleading. A fan does not have a well-defined "resistance". It makes about as much sense to talk about resistance of a fan as it does to talk about the resistance of a diode. If you try to measure the "resistance" of a fan you'll get a nonsense value that depends on the multimeter you're using. $\endgroup$ – Tom van der Zanden Jan 9 at 17:29

Late to the party but still...

The noise could be caused by the lubrication of the fan ...when you turn on the fan, the lubrication is seated down. As the fan spins, the lubrication gets all over the bearing thus centering the fan reducing the vibrations aka noise.

  • $\begingroup$ It could also be the lubrication/grease offering resistance to the fan's rotation and gradually heating up from the friction until it no longer creates (excess) resistance. This also explains why the current decreases after a while, as the resistance to rotation decreases. $\endgroup$ – Tom van der Zanden Jan 9 at 20:57

I propose examining the current voltage of the motor and the arm. The fluctuation of voltage causes the noise.

  • $\begingroup$ The voltage is constant, but the current is not. Do you know what could be causing the higher current in the beginning? $\endgroup$ – meyfa Jul 21 '18 at 10:48

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