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Topic: 3 or 4 wire fan: How to? (Read 696 times) previous topic - next topic

Milou

Hello,

for a project I want to apply two 120 mm 12V fans (not for computer cooling). The ones I got have only two wires and work always on full speed (about 90 cfm). The full speed is not enough for me, so I looked for fans with about 150 cfm (at full speed). All I found have three or four wires (eg. this one http://www.frozencpu.com/products/12944/fan-858/Sunon_120mm_x_25mm_Precision_Ball_Bearing_Fan_-1500_CFM_PMD1212PTB1-A.html?tl=g36c435s1106). Since I have already done the wiring and don't want to change, I wonder if I could use such fans (my Arduino only controls, wether the fans will run or not, i.e. wether they get power or not). At the end of my wiring solution I added a box for the remaining wires. If necessary I could add some electronics inside to make the fans running at full speed, but if possible I want to avoid to send control signals through the third or third and fourth wire.

Can anyone help me solving my problem?

1ChicagoDave

Yes, those 3 & 4 wire computer fans will usually run at full speed just fine by only connecting the +V & GND wires. Mine do, anyway.


liudr

There is no spec sheet on the fan you provided the link to. I suspect the fan runs on 12V so there is a 12V pin, and gnd pin. Then there is an optical encoder that needs 5V input and output pulses to tell you how fast it is running at.

dc42

If it is a standard computer-type fan, then the red wire is power (+12V) and black is ground. On a 3-wire fan, the third (usually yellow) wire is an open-collector output from the tacho. Leave it disconnected if you are not interested in measuring the fan speed. On a 4-wire fan, the 4th wire is the PWM input, used to control the fan speed. If you leave it disconnected, the fan runs at full speed.
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liudr

Sorry my guess was wrong. Good to know. Thanks dc42

Milou

Thank you all for your information. This helps a lot.

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