I have an application where I want to control the speed of an instrument
type axial fan to achieve the least noise and only turning on or
speeding up the fan when the inside of a case starts warming up.

I've played with a few two wire brushless fans with series resistors and
they don't start up reliably with enough series ohms to get low running
speeds. It appears that the brushless switch does not like this - fair
enough, I can understand that might happen.

I've also seen three wire fans online from places selling PC bits. Does
Anyone know what the third wire does please?

Is it just an output back to the PC telling it that the fan is running?
Is it a tacho output so the software can display fan speed for nerds
that like that sort of thing?
Is it a control input? Is is PWM to control the speed or even an
analogue voltage input to vary the speed?

I have yet to find any design info on these fans as I suppose they are
sold as fit and forget PC replacements.

TIA

Bob

On Wed, 29 Jun 2016 12:11:35 +0100, Bob Minchin
wrote:

I have an application where I want to control the speed of an instrument
type axial fan to achieve the least noise and only turning on or
speeding up the fan when the inside of a case starts warming up.

I've played with a few two wire brushless fans with series resistors and
they don't start up reliably with enough series ohms to get low running
speeds. It appears that the brushless switch does not like this - fair
enough, I can understand that might happen.

Have you tried putting a reasonably size (capacity) across the
resistor Bob? It would have to be of sufficient voltage to deal with
the supply line (so 12+ V)

I've also seen three wire fans online from places selling PC bits. Does
Anyone know what the third wire does please?

Is it just an output back to the PC telling it that the fan is running?

Typically yes So when you run something like SpeedFan you can see the
fan revs.

Is it a tacho output so the software can display fan speed for nerds
that like that sort of thing?

Yes.

Is it a control input? Is is PWM to control the speed or even an
analogue voltage input to vary the speed?

I think they can do that with 3 wire fans yes.

I have yet to find any design info on these fans as I suppose they are
sold as fit and forget PC replacements.

http://www.pcbheaven.com/wikipages/How_PC_Fans_Work/

Cheers, T i m

Bob Minchin wrote:

I've also seen three wire fans online from places selling PC bits. Does
Anyone know what the third wire does please?

I think the 3-wire have GNV/12V/PWM-in and 4-wire additionally have
TACHO-out.

To quieten my HTPC I used a variable fan controller which gives finer
control than the old 12V-5V=7V trick, I can't remember where I got mine
from, I should imagine eBay has several on offer, if not I can soon whip
the lid off ...

On Wednesday, 29 June 2016 12:12:58 UTC+1, Bob Minchin wrote:
I've also seen three wire fans online from places selling PC bits. Does
Anyone know what the third wire does please?

2-wire fans /can/ be controlled by PWM on the power wires but there is no feedback loop.

3rd wire is a tacho sensor reporting fan speed back to the PC.

4th wire is a PWM control wire.

http://www.pcbheaven.com/circuitpage...an_Controller/

http://www.pcbheaven.com/circuitpage...an_Controller/

http://www.overclockers.com/pwm-fan-controller/

Owain

On Wed, 29 Jun 2016 12:11:35 +0100, Bob Minchin
wrote:

I have an application where I want to control the speed of an instrument
type axial fan to achieve the least noise and only turning on or
speeding up the fan when the inside of a case starts warming up.

I've played with a few two wire brushless fans with series resistors and
they don't start up reliably with enough series ohms to get low running
speeds. It appears that the brushless switch does not like this - fair
enough, I can understand that might happen.

I've also seen three wire fans online from places selling PC bits. Does
Anyone know what the third wire does please?

Is it just an output back to the PC telling it that the fan is running?
Is it a tacho output so the software can display fan speed for nerds
that like that sort of thing?
Is it a control input? Is is PWM to control the speed or even an
analogue voltage input to vary the speed?

I have yet to find any design info on these fans as I suppose they are
sold as fit and forget PC replacements.

TIA

Bob



--

Graham.

%Profound_observation%

On 29/06/16 12:11, Bob Minchin wrote:
I have an application where I want to control the speed of an instrument
type axial fan to achieve the least noise and only turning on or
speeding up the fan when the inside of a case starts warming up.

I've played with a few two wire brushless fans with series resistors and
they don't start up reliably with enough series ohms to get low running
speeds. It appears that the brushless switch does not like this - fair
enough, I can understand that might happen.

I've also seen three wire fans online from places selling PC bits. Does
Anyone know what the third wire does please?


Is it a tacho output so the software can display fan speed for nerds

This one ^

There are 4 wire fans (rarer) with speed control.

T i m wrote:
Have you tried putting a reasonably size (capacity) across the
resistor Bob? It would have to be of sufficient voltage to deal with
the supply line (so 12+ V)
Thanks Tim,
I have indeed done this successfully on other jobs. The capacitor
differentiates the rising edge of the supply voltage and kicks the fan
into life and it then slows with the time constant of the parallel R-C
network. down to a speed set by the resistor

However for this application, the fan will might well run 24-7 or for
long periods and so won't get regular start up pulses.

I suppose I could do something clever with the tacho output to give it a
kick if it stops.


Bob

On Wed, 29 Jun 2016 12:11:35 +0100, Bob Minchin
wrote:

I have an application where I want to control the speed of an instrument
type axial fan to achieve the least noise and only turning on or
speeding up the fan when the inside of a case starts warming up.

Try google or ebay for "fan temperature control", maybe?

For instance: 6 US dollars gets you "12V PWM PC CPU Fan Temperature Control
Speed Controller Module High-Temp Alarm" http://r.ebay.com/8RSVdT, which used
the 3rd wire for a stall alarm, adjustable temperature ranges, minimum PWM
output and PWM characteristic.


Thomas Prufer

Bob Minchin wrote:
I have an application where I want to control the speed of an instrument
type axial fan to achieve the least noise and only turning on or
speeding up the fan when the inside of a case starts warming up.

I've played with a few two wire brushless fans with series resistors and
they don't start up reliably with enough series ohms to get low running
speeds. It appears that the brushless switch does not like this - fair
enough, I can understand that might happen.

I've also seen three wire fans online from places selling PC bits. Does
Anyone know what the third wire does please?

Is it just an output back to the PC telling it that the fan is running?
Is it a tacho output so the software can display fan speed for nerds
that like that sort of thing?
Is it a control input? Is is PWM to control the speed or even an
analogue voltage input to vary the speed?

I have yet to find any design info on these fans as I suppose they are
sold as fit and forget PC replacements.

TIA

Bob
Thanks for all the replies chaps and no one mentioned Brexit

DIY is getting back to its old self again.

I'd like to know this as well, as speedfan seems to suggest my machine has
the right chips to detect the temperatures and so one supposes with the
right fans and connections the motherboard should be capable of it, but the
current fans seem to be set to flat out and the thing runs mega cool, but
sounds like a hovercraft.
Brian

--
----- -
This newsgroup posting comes to you directly from...
The Sofa of Brian Gaff...

Blind user, so no pictures please!
"Bob Minchin" wrote in message
...
I have an application where I want to control the speed of an instrument
type axial fan to achieve the least noise and only turning on or speeding
up the fan when the inside of a case starts warming up.

I've played with a few two wire brushless fans with series resistors and
they don't start up reliably with enough series ohms to get low running
speeds. It appears that the brushless switch does not like this - fair
enough, I can understand that might happen.

I've also seen three wire fans online from places selling PC bits. Does
Anyone know what the third wire does please?

Is it just an output back to the PC telling it that the fan is running?
Is it a tacho output so the software can display fan speed for nerds that
like that sort of thing?
Is it a control input? Is is PWM to control the speed or even an analogue
voltage input to vary the speed?

I have yet to find any design info on these fans as I suppose they are
sold as fit and forget PC replacements.

TIA

Bob

On 29/06/16 12:11, Bob Minchin wrote:
I have an application where I want to control the speed of an instrument
type axial fan to achieve the least noise and only turning on or
speeding up the fan when the inside of a case starts warming up.

I've played with a few two wire brushless fans with series resistors and
they don't start up reliably with enough series ohms to get low running
speeds. It appears that the brushless switch does not like this - fair
enough, I can understand that might happen.

I've also seen three wire fans online from places selling PC bits. Does
Anyone know what the third wire does please?

Is it just an output back to the PC telling it that the fan is running?
Is it a tacho output so the software can display fan speed for nerds
that like that sort of thing?
Is it a control input? Is is PWM to control the speed or even an
analogue voltage input to vary the speed?

I have yet to find any design info on these fans as I suppose they are
sold as fit and forget PC replacements.

TIA

Bob
Check out model brushless motor controllers.


--
Those who want slavery should have the grace to name it by its proper
name. They must face the full meaning of that which they are advocating
or condoning; the full, exact, specific meaning of collectivism, of its
logical implications, of the principles upon which it is based, and of
the ultimate consequences to which these principles will lead. They must
face it, then decide whether this is what they want or not.

Ayn Rand.

Bob Minchin wrote:
I have an application where I want to control the speed of an
instrument type axial fan to achieve the least noise and only turning
on or speeding up the fan when the inside of a case starts warming up.

I've played with a few two wire brushless fans with series resistors
and they don't start up reliably with enough series ohms to get low
running speeds. It appears that the brushless switch does not like
this - fair enough, I can understand that might happen.

I've also seen three wire fans online from places selling PC bits.
Does Anyone know what the third wire does please?

Is it just an output back to the PC telling it that the fan is running?
Is it a tacho output so the software can display fan speed for nerds
that like that sort of thing?
Is it a control input? Is is PWM to control the speed or even an
analogue voltage input to vary the speed?

I have yet to find any design info on these fans as I suppose they are
sold as fit and forget PC replacements.

TIA

Bob
Use a 2 wire fan with an ntc thermistor?

On Wed, 29 Jun 2016 14:22:09 +0100, Bob Minchin
wrote:

T i m wrote:
Have you tried putting a reasonably size (capacity) across the
resistor Bob? It would have to be of sufficient voltage to deal with
the supply line (so 12+ V)

Thanks Tim,

I have indeed done this successfully on other jobs. The capacitor
differentiates the rising edge of the supply voltage and kicks the fan
into life and it then slows with the time constant of the parallel R-C
network. down to a speed set by the resistor.

Yeah, that's what I meant. ;-)

However for this application, the fan will might well run 24-7 or for
long periods and so won't get regular start up pulses.

But it only needs one doesn't it? As long as you set the minimum revs
such that it doesn't stall it won't need to re-start?

I suppose I could do something clever with the tacho output to give it a
kick if it stops.

Like a lot of the later CPU fans do in fact. You stop them, they sit
there for a couple of seconds and re-start again. ;-)

Cheers, T i m

Capitol wrote:
Bob Minchin wrote:
I have an application where I want to control the speed of an
instrument type axial fan to achieve the least noise and only turning
on or speeding up the fan when the inside of a case starts warming up.

I've played with a few two wire brushless fans with series resistors
and they don't start up reliably with enough series ohms to get low
running speeds. It appears that the brushless switch does not like
this - fair enough, I can understand that might happen.

I've also seen three wire fans online from places selling PC bits.
Does Anyone know what the third wire does please?

Is it just an output back to the PC telling it that the fan is running?
Is it a tacho output so the software can display fan speed for nerds
that like that sort of thing?
Is it a control input? Is is PWM to control the speed or even an
analogue voltage input to vary the speed?

I have yet to find any design info on these fans as I suppose they are
sold as fit and forget PC replacements.

TIA

Bob
Use a 2 wire fan with an ntc thermistor?
No this will not work as I have indicated above. Too high a resistance
and the fan won't start.
Selecting the resistor so it will start reliably (with out a capacitor
differentiator) does not drop the speed by very much.

Bob Minchin wrote:
Capitol wrote:
Bob Minchin wrote:
I have an application where I want to control the speed of an
instrument type axial fan to achieve the least noise and only turning
on or speeding up the fan when the inside of a case starts warming up.

I've played with a few two wire brushless fans with series resistors
and they don't start up reliably with enough series ohms to get low
running speeds. It appears that the brushless switch does not like
this - fair enough, I can understand that might happen.

I've also seen three wire fans online from places selling PC bits.
Does Anyone know what the third wire does please?

Is it just an output back to the PC telling it that the fan is running?
Is it a tacho output so the software can display fan speed for nerds
that like that sort of thing?
Is it a control input? Is is PWM to control the speed or even an
analogue voltage input to vary the speed?

I have yet to find any design info on these fans as I suppose they are
sold as fit and forget PC replacements.

TIA

Bob
Use a 2 wire fan with an ntc thermistor?
No this will not work as I have indicated above. Too high a resistance
and the fan won't start.
Selecting the resistor so it will start reliably (with out a capacitor
differentiator) does not drop the speed by very much.
How about a PTC and NTC parallel combination. The PTC uses the
motor current for heating, the NTC increases the voltage available.

Alternatively use a 3 wire fan and use the tacho output to switch a
fet across an NTC thermistor.

On 29/06/2016 12:11, Bob Minchin wrote:
I have an application where I want to control the speed of an instrument
type axial fan to achieve the least noise and only turning on or
speeding up the fan when the inside of a case starts warming up.

I've played with a few two wire brushless fans with series resistors and
they don't start up reliably with enough series ohms to get low running
speeds. It appears that the brushless switch does not like this - fair
enough, I can understand that might happen.

I've also seen three wire fans online from places selling PC bits. Does
Anyone know what the third wire does please?

Is it just an output back to the PC telling it that the fan is running?
Is it a tacho output so the software can display fan speed for nerds
that like that sort of thing?
Is it a control input? Is is PWM to control the speed or even an
analogue voltage input to vary the speed?

I have yet to find any design info on these fans as I suppose they are
sold as fit and forget PC replacements.


Google will let you find out about 4 wire PC fans often used for CPUs.
They appear to use PWM.


--
Michael Chare

---
This email has been checked for viruses by Avast antivirus software.
https://www.avast.com/antivirus

On Wed, 29 Jun 2016 19:53:06 +0100, Bob Minchin wrote:

Use a 2 wire fan with an ntc thermistor?

No this will not work as I have indicated above. Too high a resistance
and the fan won't start.

Choose the type of thermistor that is low resistace cold but high
hot. Low at start provides the required start umpf, once running the
current draw warms the thermistor which increase it's resistance,
drops more volts, slows the fan. That's a PTC type isn't it? Might be
tricky to find one with suitable cold/hot resistances though

Failing that use the MIC502 PWM speed control chip, or some other PWM
method.

As for the various forms of PC fans has google disappeared in your
part of the world? "3 wire pc fan":

http://www.pcbheaven.com/wikipages/How_PC_Fans_Work/

--
Cheers
Dave.

On Fri, 01 Jul 2016 21:41:23 +0100 (BST), "Dave Liquorice"
wrote:

snip

Failing that use the MIC502 PWM speed control chip, or some other PWM
method.


Or an Arduino Nano, a FET and thermistor and make it do exactly what
you want. ;-)

Cheers, T i m

On Wednesday, 29 June 2016 12:12:58 UTC+1, Bob Minchin wrote:
I have an application where I want to control the speed of an instrument
type axial fan to achieve the least noise and only turning on or
speeding up the fan when the inside of a case starts warming up.

I've played with a few two wire brushless fans with series resistors and
they don't start up reliably with enough series ohms to get low running
speeds. It appears that the brushless switch does not like this - fair
enough, I can understand that might happen.

I've also seen three wire fans online from places selling PC bits. Does
Anyone know what the third wire does please?

Is it just an output back to the PC telling it that the fan is running?
Is it a tacho output so the software can display fan speed for nerds
that like that sort of thing?
Is it a control input? Is is PWM to control the speed or even an
analogue voltage input to vary the speed?

I have yet to find any design info on these fans as I suppose they are
sold as fit and forget PC replacements.

Modern chips function quite well in clean cases even when a fan is not running (or fitted) they slow down their own working speed to cope. So if you have a fan and it is running don't **** around in the nebula of 'trons.

PS:
I saw a video of this on Youtube just prior to all the Brexitstentialism.