Can I run a "brushless DC FAN" backwards?

Open one up and swap the hall switch connections?

Grant.

It would work if you could mirror *everything*. If it uses a Hall-effect sensor, you would have to mirror the position of the sensor.

But that would create a reversed fan, not a reversible one.

Probably not; they're quite far from symmetrical.

Use two fans and switch the voltage accord>

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I think you've answered your own question here - use the two fans.

But be sure that the one that's not running doesn't provide a sneak path for the air that the other one is supposed to be moving past the work area.

Have Fun! Rich

Brushless motors that I am familiar with have three wires connecting them to a controller board. swap any two of those wires and the motor reverses. It should be easy to do with a DPDT relay. Please let us know how it works out.

My Email address is >I have a project that needs reversible fans.

John Ferrell W8CCW

But "muffin" fans generally have the controller built-in. IF they have a third wire it's for speed sensing. ...Jim Thompson

Way cool that W8CCW knows how to run fans counter colckwise .... .. ;-)

Looks like I'm stuck with two fans back to back.

A reversible BRUSHLESS fan ? They smoke when reverse powered - and they won't even blow the smoke away.

G=B2

The intervention must be performed between the actual motor and controller. The above links are the shallow and deep ends of the brushless pool for Radio Control model airplanes. Note the prices on the Castle controllers!

I suppose it could be that there are motors called brushless that are not three phase devices.

Swap any two MOTOR wires!

John Ferrell W8CCW

Common fan motors are two phase, sometimes on applied power they kick a bit before spinning. One 4 pin Hall effect with complementary outputs, or simple 3 pin Hall plus a transistor inverter. Pulse output (tacho) is another open collector transistor hanging off the Hall device.

True for three phase, swap the Hall drive for two phase, I already posted that.

Yes, but the controller just senses the magnet (on rotor) position, thus is a simply a Hall device with or plus an inverter for the other coil.

Better class motors for say CD spindle drive, have three Halls for feedback (couple I dismantled recently had that. So do the slow floppy spin motors, but they have an extra magnet and Hall outside the rotor for (I guess) the Index pulse. These motors had three phase drive to stator coils.

Grant.

PC fans are 2-phase.

Sensors are no longer used with the current technology. The controller does it all.

John Ferrell W8CCW

Cut the blades from the hub & glue back with opposite pitch.

-- A host is a host from coast to snipped-for-privacy@nrk.com & no one will talk to a host that's close........[v].(301) 56-LINUX Unless the host (that isn't close).........................pob 1433 is busy, hung or dead....................................20915-1433

Yes you can.

No it isnt.

You need to replace the controller.

No they wont, much less in fact.

Rethink your needs.

Just physically turn it over. The mountings are symmetric for just that reason.

As I stated in the first line of my original posting, I need a REVERSIBLE muffin fan. I already know how to run it forwards, so I asked about backwards.

Only if it is 40 years old already and runs on DC.

And PM. ...Jim Thompson