What does FG stand for?

Question

I have an old 12V cooler master fan that I am converting into a fume extractor for soldering and am connecting it to a standard 12v computer power supply. I am trying to wire it and am confused about one thing.

On the fan's label it has a coding for the different wire colors (red, black, and white) and it says:

red +

black -

white FG

I have looked up FG on google all over the place but can't seem to find anything that says what it stands for. I was thinking that it might be "Ground" but then what would the black negative wire be? Maybe I just have a fundamental misunderstanding (pretty new to all of this electronics stuff)

I did connect the black wire on the fan to a black wire on my power supply and the red wire on the fan to a yellow wire on the power supply (white wire connected to nothing) and it turned on and seemed to be working fine but I want to make sure that this is actually a correct wiring and isn't going to cause any problems in the future.

..which is used to determine how fast the fan is rotating. You can just leave the FG wire unconnected. That will not cause any problems. — Bimpelrekkie, Feb 02 '16 at 16:00

score 19 · Accepted Answer · edited Feb 02 '16 at 16:51

19

FG stands for Frequency Generator (or Feedback Generator), it has an output with a frequency proportional to the fans speed. It is used by the CPU to determine the fans speed.

Some (older) fans have an extra winding internally and the FG signal is a sinusoid with both amplitude and frequency proportional to fan speed.

Modern fans almost exclusively use a Hall-Effect sensor and the signal is an open-collector square-wave signal where the frequency is proportional to fan speed. Peak voltage is determined by the magnitude of the power supply that feeds the pull-up resistor.

edited Feb 02 '16 at 16:51

Dwayne Reid

23,792
2
38
70

answered Feb 02 '16 at 15:54

Steve G

5,305
1
14
24

2

great! so just to be clear, if i'm using this just as a fan to pull soldering fumes out, i can safely leave the FG wire unconnected? – celeriko Feb 02 '16 at 15:59
4

@celeriko yes. Leave it disconnected. – Steve G Feb 02 '16 at 16:01

Jose Enrique Calderon · Answer 2 · 2019-03-21T09:41:15.173

2

Be careful. I seen AC-DC power suppliers labeling "FG" for the frame ground. That means, attaching to the metal of the device.

edited Mar 21 '19 at 09:41

answered Oct 14 '18 at 00:35

Jose Enrique Calderon

139
7

score -1 · Answer 3 · answered May 10 '20 at 01:32

-1

I'm pretty sure that FG here stands for "floating ground", which is an isolated ground for the analog circuits inside the power supply.

answered May 10 '20 at 01:32

BlackPenguin

171
1
6

2

It's a fan, not a power supply. See the accepted answer. – Transistor May 10 '20 at 07:12

What does FG stand for?

3 Answers3