Yo guys,

I bought a fan on aliexpress. SInce I couldnt find a powerful exctractor I thought I would take a powerful fan and reverse the motor. I did. But I encountered an unexpected issue.
Whereas the fan consummed 30-40w originally, it consummed only 15w as an extractor.
What do you think happened ?
I join a picture. As you can see it works with a capacitor. And of course its an AC motor since there are 3 wires.
All I did was switching the blue and yellow wires.

 

If you are using the fan with any resistance to the air flow, the current will decrease.
You can only reverse it if the two windings measure equal resistance.

 

Yo

Can you elaborate I'm not sure I follow you

 

If you run a fan in free air, and then in a duct or other restriction to air flow, the motor current tends to decrease.
As to the motor windings, they should show 2 equal winding resistances if it is desired to change the direction of rotation.

 

I have a similar fan. It utilizes a start capacitor. If I change the location of the starter the fan runs slower than designed.

I thought I would take a powerful fan and reverse the motor.

When you say you "reversed" the motor what are you saying? You wanted to reverse the direction of rotation? Or did you have a squirrel cage type fan? If you turn them around they don't move as much air and the motor will draw less power.

Really, we need a little better description of what it is you've done. Swapping a few wires won't reverse an induction motor. All you're doing - if your motor is like mine - is change the start coil into a run coil and the run coil into a start coil. Or at least that's what I think is going on when you swap the location of the cap.

 

Swapping a few wires won't reverse an induction motor. All you're doing - if your motor is like mine - is change the start coil into a run coil and the run coil into a start coil. Or at least that's what I think is going on when you swap the location of the cap.

A PSC (permanent start cap) induction motor has two equal windings, which means it can be reversed by simply by swapping the cap over to the other winding i.e start to run and vice-versa.
This is often achieved with a SPDT switch with centre off.
Most fans are designed for uni-directional though.

 

Some "permanent split capacitor" motors have two windings that are not identical . They are also not intended to ever be reversed.
In addition, it looks like the device shown is a blower, not a fan. There is a big difference in that blowers are not intended to operate in the reversed direction. So that alone explains the different power demand.

 

A simple resistance check can solve it.

 

Even for a reversible motor with equal windings, most blowers operate much different when spun in the reverse direction. And that alone will change the current drawn quite a bit.

 

The PSC (permanent start cap) induction motor is the mainstay of most small fans, all the ceiling fans in my place are these. It is very common to reverse a PSC motor with the method I mentioned when used for other purposes.
Both windings are identical.

 

Based on the small amount that I see in te photo my guess is that the device is a blower, not a fan. And even fans often perform differently when run backwards. I own both a reversible fan and non-reversible fans, and the blade structures are rather different.