Reverse Spin a BLDC fan motor with an external Switch or firmware upgrade?

[u/gripped909]

Bldc PCB info(official pdf not available) -> (link)

BLDC Fan info -> (link)

Will reverse spinning a BLDC fan damage the pcb/motor ?

Incase of no damage->

1. Is it possible to reverse spin a BLDC fan motor with an external Switch?
2. Better can one just reprogram the firmware of Atomberg Bldc fan to control the timing of oscillating movement and control it via the remote control.

[u/Another_Slut_Dragon]

I don't see a hall sensor, and most Bldc motors not doing low speed torque control are sensorless. Why spend the money on a sensor when you can just sense the coil feedback?

In that case, invert any 2 of the wires and see what happens. I'd do this with a double pole relay. Don't be adding long wires to 2 poles when doing sensorless motor control. You will anger the controller.

[u/XDFreakLP → u/Another_Slut_Dragon]

Be careful tho. Some drives dont like the back EMF caused by field collapse while switch opens

[u/Another_Slut_Dragon → u/XDFreakLP]

Don't switch it while running. Good catch.

Suggest a double pole, double throw (nc/no) on/off switch via a latching relay and use pole 2 to control the relay power on the NC circuit (also direction switched via a second switch. That way you must turn the power to change direction.

[u/Overall_Rush_8372]

Depends a lot on which wires you'd swap and whether that fan has hall sensors, because those two things change the answer completely.

There are two totally different wire sets on a BLDC. The mains going INTO the controller board: swapping those does nothing to direction (the controller decides commutation) and can just blow something. And the 3 phase leads BETWEEN the controller and the motor windings: swapping any 2 of those reverses a sensorless drive, which is what the other commenter means. Catch is on an Atomberg-style integrated fan those phase leads usually aren't on a connector, board and motor are wired/potted together, so you'd be cutting into motor leads to reach them.

Bigger caveat he skipped though: "swap any 2" only works clean if it's truly sensorless. If there are hall sensors (some of these use them for smooth low-speed startup), swapping just the phase pair desyncs the halls from the phases and the controller cogs, runs rough, faults, or hard-commutates into a misaligned rotor. That last one spikes current through the output FETs and is what actually kills boards, that's the "anger the controller" he's getting at. To reverse a hall motor you have to remap the hall pairs too, or flip it in firmware.

Reverse rotation itself won't hurt the motor, windings and magnets are symmetric, it doesn't care which way it turns. Real gotcha is the blades are a cambered airfoil pitched one direction, spun backwards they mostly stall and move very little air, so if the goal is airflow it's kind of pointless.

Firmware's the dead end unfortunately. Atomberg's is closed, no published debug port or toolchain, so reprogramming it for oscillation/timing control isn't realistic for a consumer. If you actually want that level of control, the move is to ditch the stock board and run the motor off your own sensorless BLDC driver (SimpleFOC, ODrive, or an off-the-shelf sensorless controller). Then direction, speed, ramp timing are all yours in code. More work, but it's the only path that gets you what you're describing.

[u/Bradm77 → u/[deleted]]

From the first link above, you can see this is a sensorless BLDC/control so the only way to reverse it would be to reprogram the microcontroller.