Recently installed a range hood and it's not sucking up smoke very well. It's been uninstalled and checked for obstructions and none have been found. The dampers are opening and closing properly. One at the unit the other on the roof top vent. The unit is a four speed fan (450 to 920 cfm). Using a facial tissue I have to move said tissue to within 1" of the range hood to get it to suck up. I'm no electrician but can follow simple instructions after 40 years of handyman work. The only thing left to my mind is that the fan is running in reverse. So once again my question is: If the receptacle I have plugged this unit into is reversed polarity would that cause the fan motor to run in reverse?
Will a fan motor run in reverse if the receptacles polarity is reversed
electric motor
Related Solutions
With another clockwise fan from the same maker, I was able to reverse the direction by interchanging the yellow and black wires as some answers here indicated. The explanation as I understood is that the rewiring changes the winding with which the capacitor is in series and hence the starting direction is inverted.
In 3-phase motors, each of the three stator windings carry a current out of phase with others and the phase difference generates the rotating magnetic field required to cause the motion. With single-phase ones, a phase difference is engineered by splitting the single phase current into two stator windings and putting a capacitor in series with one of the windings so that there's a 90° phase difference between the currents in the two windings. This page on electric motors explains the concept with illuminating animations.
The following figure shows my guess, based on the above information, at the internal wiring of the clockwise spinning fan whose image is posted in the question, for clockwise and anti-clockwise rotations.
A point to note here is that single-phase AC itself produces a changing magnetic field - though a pulsating one, not a rotating one. But this pulsating field can be resolved, as per the double field revolving theory (the link has an excellent video of the workings by the way), into two revolving fields rotating in opposite direction to each other. These two fields produce an equal but opposite torque. On a static rotor, they'll cancel each other out. But an initial rotation makes torque in one direction greater than the other and starts up the fan.
This is what, I believe, happened when the OP switched red and yellow wires on his fan. The result was that the capacitor was in series with both windings => there was no phase difference in the currents in the windings. When he added a slight initial rotation, the fan continued spinning in the nudged direction.
I'm just tunnel-visioned. I was sure I had plugged it into the correct socket, but no.
Stupid User Trick
Sorry
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Best Answer
Just crappy fan design and misleading ratings (450-920 cfm with no duct at all, and terrible fall off with any normal resistance - or else it's an outright lie.) What is your actual duct arrangement (size, length, number of turns?)
If the fan was running in reverse, the tissue would be blown away, not sucked up from any distance. A/C motors run on current that reverses polarity many times per second, and their direction of operation is not affected by that.
Either return it, or scrap the fan and replace with a quality duct fan designed for range hood service (grease, moisture, heat) - might as well go for quiet as well while you are investing in quality.