Electronics > Beginners
How to measure RPM of DC fan?
shai:
I have a fan that is 30x30mm diameter and the hub is about 16mm diameter (when looking from the top). I read that you can use a Tachometer, but after searching for those on Amazon, I see that you need to apply tape to the object you're measuring RPM of and I'm not sure if there's enough space for the tape size required. Is there a better way to measure a small DC fan's RPM? My fan only has 12v/GND leads, no yellow wire for hall effect sensor. Any help appreciated!
Reason for this is because I tore out a regular 30x30x10 fan's DC "magnetic motor" and fitting my own bearing on it for a custom fan. So I want to swap bearings and see how they affect RPM. (but this is a separate topic :))
ogden:
In case you have oscilloscope, you need straight core (thru-hole vertical) inductor. No need to glue magnet to rotor, because fan have built-in one :)
http://paulorenato.com/index.php/electronics-diy/113-measuring-rpm-with-an-oscilloscope
Other way of measuring: flashlight+photodiode+scope. Note that LED can be used as photodiode as well.
David Hess:
The DC ripple current can also be used to measure the RPM of a DC brushless fan. Areca uses this trick on their RAID controllers to monitor the cooling fan RPM. Small expansion card sized fans with a tachometer output are not common.
Sudo_apt-get_install_yum:
Couldn’t you use the current draw of the motor to get some sort of indication of the motor speed? Higher load = higher current draw, since you know the voltage and the max RPM for that voltage.
I don’t know how accurate this is but for rough estimation it should be fine!
ogden:
--- Quote from: Sudo_apt-get_install_yum on November 26, 2018, 11:23:41 am ---Couldn’t you use the current draw of the motor to get some sort of indication of the motor speed? Higher load = higher current draw, since you know the voltage and the max RPM for that voltage.
I don’t know how accurate this is but for rough estimation it should be fine!
--- End quote ---
Waste of time. Low friction bearings can lead to faster RPM, yet lower consumption. Even audio spectrum application for mobile phone is way better tool. This looks good
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