Running a 12V DC blower having 3 wires - Page 1
Forum section: electronics / beginners

author: Adhith
author_rank: Frequent Contributor
timestamp: November 05, 2019, 03:50:51 pm
content: Hello there,I'm trying to run this blower (12V, 2.94A rated) with a DC wall adapter. I have seen a couple of post on the internet showing that the 3rd wire is a tachometer output and could be left alone while running it on a DC source. But, unfortunately I cant run this in that way. Could anyone help me out here?The second pic shows the connection terminals on to the onboard circuit in the blower. black- ground, red- input, blue- output

author: Gyro
author_rank: Super Contributor
timestamp: November 05, 2019, 06:54:55 pm
content: Hi,The markings on the PCB look quite clear. Yes, the blue wire does look like just a tachometer output. If it isn't working with +12V on the red lead relative to the black one, then the blower is probably dead (I can't see the rating label but you say it is 12V). Make sure that the blue wire is safely insulated so that it can't accidentally contact either of the other wires (shorting it could have damaged the internal circuit). Reverse polarity would probably also kill it.Does the fan make any attempt to start? Any small wobble from the impeller? Have you tried giving it a push with the power applied? - just in case the PSU isn't able to support the starting current. Is it actually drawing any supply current?

author: ArthurDent
author_rank: Super Contributor
timestamp: November 05, 2019, 09:04:48 pm
content: There isn't a lot of consistency in color coding of fan leads but quite often yellow is for the tach and blue is marked PWM for a pulse width modulating control lead to the motor. You can check this by connecting about a 1K small resistor to the blue lead and touching the other end of the resistor to either common or +5 and see if the fan runs. I've run some like this at full speed by just connecting the lead through a resistor to the positive supply. If you want to control the speed, you probably should use PWM instead of applying a lower D.C. voltage to the blue lead because if the control transistor isn't full on/off at about 25Khz, it will now be dissipating heat and might fail.Here's a wiring diagram I found on line that also has the yellow 4th lead for a tach.

author: Adhith
author_rank: Frequent Contributor
timestamp: November 06, 2019, 11:52:49 am
content: Quote from: Gyro on November 05, 2019, 06:54:55 pmThank you very much for the reply. The blower is surely 12V rated. I have connected the red and black wires respectively to the DC adapter but it didn't worked. Checked with another adapter and got the same result. The adapters are 5A rated ones which I believe, would be enough for this 3A rated blower. While connecting the multi meter, its found that there is no current draw while powering the blower. I was wondering whether the tacho meter output is acting as any kind of relay to power the blower.

author: Adhith
author_rank: Frequent Contributor
timestamp: November 06, 2019, 11:55:40 am
content: Quote from: ArthurDent on November 05, 2019, 09:04:48 pmThank you very much for your help. I have checked the method you mentioned with the 1K resistor. Still nothing. Since the blue wire terminal is labelled as output on the board, Is there a chance that it could be a PWM signal input?

author: mikerj
author_rank: Super Contributor
timestamp: November 06, 2019, 12:38:37 pm
content: That fan looks like aDelta BFB1012EH(or a clone) in which case the third wire is a tachometer output. If the impeller spins freely by hand (i.e. bearings not seized) then it sounds like there is a fault within the motor drive circuit.

author: pcmad
author_rank: Regular Contributor
timestamp: December 06, 2019, 12:09:05 am
content: looks like a standard pc cooling fan the third wire (blue) is a tachometer output aka rpm