# How can single phase induction motor's direction be reversed?

My house has a ceiling fan which has 2 wires which are connected to a capacitor, and Iam able to control the velocity and direction. After looking about these motors on the web I found out its probably a single phase induction motor.

So, this motor has 2 windings, one for driving the actual motor and the other for either starting the motor or keeping the motor spinning. I don't know which of these my 3-wire capacitor is doing. What I know is that the capacitor provides a phase change in the second winding so it can apply force when the motor is running.

So we have 2 wires to the motor, and they are in different phases, which makes the magnetic fields have different directions at different times. But: how can my fan spin the other direction as well?

Typically reversing the fan motor is done like this, an SPDT switch changes which end of run capacitor is connected to the feed, and in doing so changes which winding sees the advanced signal.

simulate this circuit – Schematic created using CircuitLab

• I'm glad tee that the anonymous coward is not at all partisan! Commented Apr 3 at 0:00
• what would be thje advanced signal? Commented Apr 5 at 14:43
• a series capacitor causes the current and voltage peaks to come earlier in the cycle, Commented Apr 5 at 22:32
• How can this reverse the magnetic field? Commented Apr 8 at 13:52
• current is also flowing the opposite direction Commented Apr 8 at 20:42

My concern with Andy aka's solution is that when the capacitor is moved from the aux winding to the main winding, the current in the aux winding may increase, and that increase may be beyond what the winding was designed for.

Here is an alternate way to swap the wires.

My schematic is modified from the same source as Andy aka's i.e. a paper uploaded by Thomas A. Lipo.

The unmodified schematic is here:

• this overload is certainly a possibility, however motors that are designed to be easily reversable do it by just swapping main and auxillary (as is it just swapping the feed point of one of the supoply lines) Commented Apr 2 at 21:57
• Would the down-voter care to explain what they think is wrong with my answer? Commented Apr 2 at 21:59

how can my fan spin the other direction

Well, I can't tell you precisely how they do it in your fan but consider this as a possibility: -

You swap the windings over. Use the capacitor on the regular winding and use the start winding with the AC supply and, it'll rotate in the opposite direction. Here's how it looks normally: -

Image from here and, if we swap stuff around it'll run in reverse: -

• My concern would be that the two windings may not be designed for the same current. Moving the cap from the aux winding to the main winding will probably increase the current in the aux winding, and may cause it burn it out. Commented Apr 2 at 20:21
• @MathKeepsMeBusy It's a valid concern and would be almost certainly true if the motor only had a start winding that was disengaged when the motor speed was sufficient. I'm offering a solution and there may be other that are more appropriate if we knew the actual motor spec. Commented Apr 2 at 20:31
• I'm not sure who downvoted you, but it wasn't me. Commented Apr 2 at 21:59
• your rewiring is equivalent to merely swapping the upper feed point to the other side of the capacitor. Commented Apr 2 at 21:59
• Assuming motor terminals are called A,B,C,D then (A)---||--- (feed)---(C) becomes (A)---(feed)---||---(C) to reverse the motor, I'm not saying it doesn;'t work, I am saying you're drawing it the hard way. Commented Apr 2 at 22:43