Swapping pc fans control circuit.

[cjoooooooo152]

So while bored in lockdown and after my portable desk fan died the other day I decided to start a little project.

I have an old dead 220mm case fan from an old pc and figured I'd turn it into a desk fan.

To do this i decided to remove the control circuit from an unused smaller pc fan that I had lying around, a 80mm amd stock fan.

I check the amd fans function before starting and it worked.
I have a little test rig for power which works hence testing the amd fan and others.
Both fans are 4 coiled brushless dc motors, the difference being size

I figured that there maybe some compatibility issue with the amount of current required to drive the bigger fan with the smaller fan controller which is why I'm here.

I should add that the swap didn't work which is why I'm looking for advice.

The ratings for the fans are as followed

amd stock fan
12v 0.55a

220mm fan
12v 0.28a

Feel free to ask any questions or for photos

Chris

[Benta]

Important thing is the type of connection: 2-wire, 3-wire or 4-wire?
This detemines the type of controller you need.

[cjoooooooo152]

Well the smaller amd fan is a 4 pin and the larger fan was a 2 pin however the ciruitry on the larger 2 pin had 2 unused solder points labelled vr and pg.

The coils/mounts have identical wiring feeding back into the circuitry

I'm assuming that the problem would be different phasing? If so would there be a way to change it?
I can upload pictures if that would help.

Thanks for the reply.

[Algoma]

If you're looking to control the fan speeds, often simply controlling the DC voltage is the best way, either DC-DC converter, or simply drop the voltage across a large enough power resistor (3W+) if you don't mind a lack efficiency and a tiny heater along with your fan, even an adjustable LM317 regulator could work (with a heatsink).  Many 12V fans will operate as low as 6V just fine, but may require a boost to get going. it all depends on the controller's hall effect sensor being able to track the position of the rotor.

Driving many DC fans with PWM cause the controller to reset on each pulse, so they have a dedicated (optional) line for PWM input to the controller.

[cjoooooooo152]

I'm trying to get a 220mm fan to work with a 80mm fans controller

[Algoma]

Curious challenge, kind of like trying to get a car to work with a motorcycle engine. Is the controller for the 220mm lacking a specific feature you need?

Quite often the windings of the motor are soldered directly to the controller PCB, and given its a brushless motor, the hall effect sensors in the controller chip itself need to be close enough to the magnets in the hub of the fan to detect and control its rotation.

[Algoma]

220mm fan is dead, Apologies for my lack of reading the details.. Thankfully DC fans are pretty simple devices. Biggest challenge is getting into the controllers. They're not really designed to be very serviceable. polarity and continuity of the windings are the main items.

Often the fan controller is expecting a certain perforance curve, and without feedback from the hall effect sensor about proper rotation will shut down for a few seconds and try another startup sequence again. Overall to prevent overheating and burnout of the coils.

in a simplified way, as each magnet of the hub passes over the controller, the windings reverse polarity from a pull to a push..

You may be just as well to epoxy the hub of one motor onto the other. - Mind the bearing will likely soon fail under the additional weight of the larger fan blades.

[Benta]

OK, the situation is this:
the 2-pin fan can be controlled by varying the voltage to the fan, but only in a certain interval (eg, 7...12 V). Or by 50...100 Hz PWM of the supply voltage.
The 4-pin fan needs 12 V all the time and is controlled by a 25 kHz PWM input.

They're not really compatible.

[cjoooooooo152]

I think what i'm going to do is reinstate the coil frame onto the smaller fan, trim the blade and secure it to the inside of the 220mm blades/fam piece. Using the smaller driver to spin the lager fan piece.

Would I incounter over heating do you think?

[Benta]

Considering that a 2nd hand PC fan can be had for the price of a cappuccino, I question the sense of this whole thing.

[cjoooooooo152]

Well one because I'm bored and 2 I like problem solving and tinkering with junk because it's way more fun than throwing £20 at a crappy desk fan that has 2 speeds and looks like a bird cage.

There's nothing to be gained from throwing money at something that's not vital.

[magic]

Did you move the whole PCB or just the chip? How does it even fit into a different fan?
Is the distance between the coils/chip and the rotor the same?

[ledtester]

Well one because I'm bored and 2 I like problem solving and tinkering with junk because it's way more fun than throwing £20 at a crappy desk fan that has 2 speeds and looks like a bird cage.

There's nothing to be gained from throwing money at something that's not vital.

An idea for your next project... make your PC fan spin in reverse:

https://youtu.be/TvSjKhFGw4g

[moebiussurfing]

Hi all,

I have fried a 25$ brushless 3 pin fan Be Quiet Silent Wigs 120mm (probably by inverting polarity), and maybe this thread has some starting points to trying to fix it...

I have opened all the fan seen that uses a LA6584 IC, but maybe I'll not be able to found/buy it here.

I am not sure that the chip is fried or maybe some small component...
I don't know how to check it fine, but the 12v vcc it's on the chip pin, so, maybe the input diode is not burned.

What do you think?

Should I try to make a super simple circuit? Any link on doing that?



I am new on the forum,
Regards!

[moebiussurfing]

hey @cjoooooooo152, I would like to see the picts if you can share. Best

[moebiussurfing]

I have seen this very simple circuit:


EDIT:
This is the simpler I found.
You can replace all the driver controller with some components:

It looks promising.