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Topic: 5v pins vs I/O pins (Read 926 times) previous topic - next topic


Hi Arduino community, I could use some help on my first project.

I have four small, 5 volt computer fans that I want to control with my Uno.  Here is the datahseet-
http://www.evercool.com.tw/categories/global/fan/imges/3010.pdf The model is the EC3010M05CA, in the fourth row.

The problem I have had is that when I connect one fan up to a 5v pin and to the ground, the fan spins at high speed and creates an ideal air flow.  However, when I connect it to one of the I/O pins, it spins far slower, and even requires a push to get it started spinning.  What could be causing this difference? I thought the pins would be the same voltage and that they would have the same effect on the fan. 
Any guidance would be greatly appreciated!  I have very limited knowledge of electronics and arduino, but I'm eager to learn!


Feb 28, 2013, 06:28 am Last Edit: Feb 28, 2013, 06:30 am by JimboZA Reason: 1
Yes you have enough voltage, but nowhere near enough current... I/O pins can supply 40mA, but that motor needs 0.18A which is 180mA.

Motors should be run along these lines, through a transistor and with a flyback diode. There, the Arduino's involvement is limited to supplying control, not power.
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Your answer may already be here: https://forum.arduino.cc/index.php?topic=384198.0


Ok, that makes sense.  Thanks for your quick help!  Looks like I've got some more orders to make...

Just out of curiosity, do you know what the max current for the 5v pins is?

Coding Badly

The absolute maximum per pin is 40mA.  At 40mA you will shorten the life of the processor.  There are per-port and per-processor limits as well.

Folks on this forum generally recommend 20mA maximum.

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