DC Motor 3rd Wire Use?

.."In a 3-wire fan, first two wires are the power supply wires of the fan. The third wire, comes directly from the output of the built-in ‘Hall Sensor’ chip generates output pulses during the fan rotation. With the help of this third wire, a monitoring circuit can ‘see’ the rotation. If the monitoring circuit sees no pulses (fan off) or weak pulses (very low rpm), then it raises an alarm to inform the operator/user about the mishap!"...

https://www.electroschematics.com/3-wire-cooling-fan-monitor/

The monitoring circuit is optional....it's used as a warning system if your fan is failing to keep the computer from overheating....

GREAT!

THANK YOU SIR

Hello Solar Eagle,

first of all I appreciate your reply, it has been very helpful.

now, I need some help. on the schematic drawing it shows 5 VCC, but obviously I have 12VCC, as the motor is rated 12VDC. can I use the 12VDC for the alarm circuit VCC. changing the 5VCC to 12VCC. if this is possible, what else has to be modified to get the circuit working on 12VDC.

thank you

This is a circuit for a typical computer power supply...the 5v output on the yellow wire is generated by the hall sensor(pwm) in the fan motor itself from the 12v supply...

If you are designing the fan for some other use we would need to know the components involved...

https://www.analog.com/en/analog-dialogue/articles/how-to-control-fan-speed.html#

https://www.maximintegrated.com/en/design/technical-documents/tutorials/1/1784.html

https://usa.banggood.com/DC-12V-Temperature-Speed-Controller-Denoised-Speed-Controller-for-PC-FanAlarm-p-1615782.html?rmmds=detail-left-hotproducts&cur_warehouse=CN

Here's my guess:

The 3rd wire (F type) is frequency (speed) indicator waveform...

https://media.digikey.com/pdf/Data%20Sheets/Sunon%20PDFs/DC_Brushless_Fan&Blower_Cat.pdf

G99 in part number means F type 3rd wire.

Mostly Brushless DC motors have 3 wires and use for the special driver circuits. But the wire gives the brushless motor added pulling power.