Choosing between 2 Motor Speed Controllers, for a 5v Fan for a Mini-PC

Thread Starter

Zohar

Joined Nov 19, 2015
70
Hi All


I bought several 5v Fans (Brushless) for use as cooling for Raspberry Pi and other Mini-PCs.
All the fans that I bought use a relatively low current (relative to motors..), about 100-150mA maximum.


I would like to be able to control the speed of those fans, manually,
and so I searched eBay for the words motor speed.


2 results that repeat there quite often, are these:


The Red:
4.5-35v, 5A, 90W, 20KHz



https://www.ebay.com/itm/3V-35V-12V-24V-5A-PWM-DC-Motor-Speed-Controller-Adjustable-Switch-LED-Fan-Dimmer/132270456321


The Black:
5-16v, 10A, ??W, ??KHz



https://www.ebay.com/itm/DC-5V-16V-Motor-Speed-Regulator-PWM-LED-dimming-10A-Ultra-Switch-Module/153325681507



All of them are good for 5v,
and all of them are way beyond the 150mA of current that I need.
So in that area, they will all be good.

Yet there might be some differences,
for example the red one has a big Electrolytic capacitor.
The black one does not have a capacitor,
or maybe there's an SMD capacitor there that is much smaller.
What effect does it have on the module's operation?

And any other thing that might help choosing between the 2?

If you can, looking at their components, tell which one is better, that would be really helpful.


Thank you very much
 
Last edited:

Thread Starter

Zohar

Joined Nov 19, 2015
70
Hi Dodgydave

In the picture of the second one (the black one), we can also see that it contains an NE555,
so doesn't this mean that both are PWM?
 

shortbus

Joined Sep 30, 2009
6,979
I bought several 5v Fans (Brushless)
Pretty sure neither of them will work with a brushless motor(BLDC). BLDC motors are electronically commutated and using a dimmer type control like you linked to will only lower the voltage into the motor, not the speed of rotation. For a BLDC they use an ESC electronic speed controller, and if the fans you have will run without one that means the controller is built into the fan, something very common in PC fans.
 

Thread Starter

Zohar

Joined Nov 19, 2015
70
Well you raise a good point that I might've not been aware of.


Here is 1 fan that I purchased:


https://www.ebay.com/itm/5V-6cm-60mm-60x60x10mm-DuPont-Brushless-Lufter-PC-Computer-Cooling-Cooler-Fan/253927366875

It is 6cm in diameter.

The second fan is extactly the same manufacturer and same model, just 8cm.
Still Brushless


Both fans have only 2 wires: 5v, and Gnd.
They do not give any feedback regarding the current RPM.


So does this mean that the 2 Motor Speed Controllers that I showed above are not relevant for these fans?
 

MaxHeadRoom

Joined Jul 18, 2013
19,029
Those are typically BLDC fans, but have a DC supply and an internal sensor IC and electronics for control, some have varied the input voltage to regulate speed, you might want to whip up a simple 555 PWM controller to try it.
I have not used them this way myself, just hearsay.
Max.
 

Thread Starter

Zohar

Joined Nov 19, 2015
70
you might want to whip up a simple 555 PWM controller to try it.
The Black controller above has an NE555 on it.
On the Red module I cannot see an NE555 in the picture, but it is declared as PWM, so it should work similarly to the Black one..
So will they be good for it?

Shortbus wrote above that he thinks the modules will not be a good match for them..
 

MaxHeadRoom

Joined Jul 18, 2013
19,029
The ebay controllers mostly use the 555 in a PWM mode, it is a toss up whether they will work with those motors, the ebay version is cheap enough if you want to give it a try, or as suggested, put one together if you have the 555.
Basically you are just reducing the mean DC level.
Max.
 

Thread Starter

Zohar

Joined Nov 19, 2015
70
So from what you say,
If they won't work with the fans, then neither an NE555 that I put on a breadboard for testing..

What exactly is the problem? The fact that a BLDC otor has some circuitry inside?
Why doesn't PWM "pass" this circuitry and affect the speed?
(If it lowers the voltage, it should affect the speed, no?)
 

MaxHeadRoom

Joined Jul 18, 2013
19,029
The DC for the fan feeds an electronic commutation circuit and has the magnetic sensor built into the IC, using a external PWM in place of the DC , just by varying the DC level, this has the effect on speed of the fan.
Generally the fan design is not really intended to be used this way, but some have had some degree of success.
Max.
 

Thread Starter

Zohar

Joined Nov 19, 2015
70
I see,
so PWN in general should be avoided.

What about supplying diferent DC myself?
e.g. instead of 5v to give 3v?
(flat DC, not PWM..)
Will that work with them to reduce the speed?
 

MaxHeadRoom

Joined Jul 18, 2013
19,029
You could try the lower DC first, I didn't say that PWM should be avoided, it is an option to try, which evidently has been used by others in some cases.
Max.
 

Alec_t

Joined Sep 17, 2013
10,359
A method I've used successfully for speed control of a 2-wire BLDC fan is to connect a biased-on transistor (BJT or MOSFET) as a low-side switch for the fan, have a current-sense resistor in series with the switch, use a comparator to detect when the fan's internal commutation causes periodic dips in the sensed fan current, use the comparator output to trigger an adjustable monostable circuit, and use the monostable output to turn the transistor off, thus extending the current dip interval. This effectively modifies the commutation in a synchronous, non-conflict way and gives wide control of the speed. Depending on the internal commutation, there's no guarantee it would work with all BLDC motors.
 

Thread Starter

Zohar

Joined Nov 19, 2015
70
A method I've used successfully for speed control of a 2-wire BLDC fan is to connect a biased-on transistor (BJT or MOSFET) as a low-side switch for the fan, have a current-sense resistor in series with the switch, use a comparator to detect when the fan's internal commutation causes periodic dips in the sensed fan current, use the comparator output to trigger an adjustable monostable circuit, and use the monostable output to turn the transistor off, thus extending the current dip interval. This effectively modifies the commutation in a synchronous, non-conflict way and gives wide control of the speed. Depending on the internal commutation, there's no guarantee it would work with all BLDC motors.
Extremely advanced for me.. :)
Any chance for a really simpler solution, even if it means not as good as the one specified?
 
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