fan control 3 wire

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Dick60
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fan control 3 wire

#1 Post by Dick60 » 07 Jul 2022, 14:30

Can anybody help me how to control a 3 wire 12v fan connected to an esp8266. I prefer to use the IRF520 Mosfet.

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Re: fan control 3 wire

#2 Post by TD-er » 07 Jul 2022, 14:49

3-wire fan only has a speed-counter line.
So it only provides feedback on the speed.

This means you still need to supply a PWM signal to the 12V of the fan.
Make sure you have a diode over the fan as it may produce quite high voltage peaks when controlling it via PWM.

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Re: fan control 3 wire

#3 Post by jgrad » 07 Jul 2022, 15:01

it really depends on type of fan

see my experience in post viewtopic.php?t=8487#p51978

Dick60
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Re: fan control 3 wire

#4 Post by Dick60 » 07 Jul 2022, 15:14

So what I read in the 2 answers is, TD mentioned that the 3rd wire (yellow) is only a speed counter line. In that case I can only read the RPM. In the Jgrad post I read that there is a possibility to PWM the yellow wire or is that a wrong interpretation of the post?

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Re: fan control 3 wire

#5 Post by jgrad » 07 Jul 2022, 16:03

I dont know what type of fan you have.

i posted my experience with Helios fan (room recuperator/heat exchanger). i tested also PC processor fan - they are also PWM controlled from motherboard.

Do you have any documentation of your fan?

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Re: fan control 3 wire

#6 Post by TD-er » 07 Jul 2022, 18:17

The "old" standard for PC fans is 3 wires, where only the speed is reported back to the PC. (so called "tacho" pin)
The newer 4-wire standard has GND, 12V, tacho, PWM
N.B. the colors of these 4-wire fans is not always the same, but the black (GND) and blue (PWM) seem to be standard.

- GND (black)
- 12V (Yellow/Red)
- Tacho (Green/Yellow/White)
- PWM (blue)

There are also fans with 4 wires and 5p header.
If there is black and red, then those are always GND and 12V as far as I know.

Also there is a difference among 4-wire fans whether they accept 5V PWM of 12V PWM.

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Re: fan control 3 wire

#7 Post by Dick60 » 07 Jul 2022, 19:02

here is a link to the specs of the fan https://icecat.biz/p/tacens/3auraii12/h ... 50773.html
Hope you can do something with it otherwise I use the voltage control using the Mosfet

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Re: fan control 3 wire

#8 Post by TD-er » 07 Jul 2022, 22:34

How do you intend to control it using a mosfet?
A mosfet can be used as a near 0 Ohm resistance to switch it on and near infinite resistance to turn it off, but you can also use a mosfet as a variable resistor. (depending on the type)

I guess it is probably best to use it as a "digital" switch and thus power the fan via PWM. (not via a PWM input)

When using the mosfet as a variable resistor, you not only generate heat in the mosfet, but also may have trouble to start the fan or to keep it running if it accumulates some dust.

But running it as PWM, you have to add a diode over the fan to suppress the high voltages, just like you also need to do when driving a relay.

Dick60
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Re: fan control 3 wire

#9 Post by Dick60 » 08 Jul 2022, 06:22

It is clear for me, I use the PWM solution, tested it and works fine for me.
Thanks for the support

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