Thread: Washing machine motor

BigStick,

So far, no replies, and not surprising. It would be a big help if you stipulated which model washing machine the motor is out of.

A service guy/member might then be able to help.

There is generally a whole bunch of wires, for the various windings and speeds.

Ken

Hi Kim,

Without more information it's a bit tricky to provide precise details..

Step 1. Assuming it's capacitor start.. locate the start capacitor, and trace the wires back to the start winding.

One side of the start cap will go to neutral, and one goes to a motor winding. That's the start winding. The other end of that winding will go to 240V active.

What you need to do is reverse the connections to the start winding.

A picture would be nice...

Regards
Ray

The wikipedia has a bit on AC motors thats useful.
AC motor - Wikipedia, the free encyclopedia
For this motor scroll down to "Split-phase induction motor"

I have a washing machine motor on my bench waiting to be rebirthed. It has no start capacitor. The the start winding can be identified as a higher resistance (lower power) winding. (From memory mine was about 7 ohm on the main winding and 11 ohm on the start winding)

The lack of a start cap means a bit less startup power.

Darren

Darren
Doesn't lack of a starting cap also mean lack of direction when starting? It may start either way or just sit there and hum. (unless its a two cap motor in which case I think it will start with less startup power as you say)

Of course I could be wrong

Stuart

Hi Stuart,
Its my admittedly limited understanding that (EDIT: for motors designed without a start cap) the start winding has its phase slightly shifted by different resistance and inductance of the less significant winding. Its not shifted by as much as a cap would shift it hence the limited startup torque. When the motor gets up a bit of speed the winding is switched out.
If the motor is designed for a starting cap then you obviously can't take it out.
Of course I could have the wrong end of the stick too.
Darren

Because you cant find a cap doesnt mean it does'nt exist. The start wind insulation just may be the capacitor. This is a common trick used in TV flyback transformers, so though I couldnt swear to it, its a good bet that they save a cent or two this way.

If the motor has a capacitor the reversing is done through this. I recently wired up an induction motor so that it was reversable throught a reversing drum switch. Even if you only want to change direction of rotation permanently, it will be done through the capacitor.

I only followed the directions of my knowledeable electrical colleague so I can't advise specifics.

If there is no capacitor, I have no idea how reversing is accomplished.

Regards
Paul

Originally Posted by rrobor

Because you cant find a cap doesnt mean it does'nt exist. The start wind insulation just may be the capacitor. This is a common trick used in TV flyback transformers, so though I couldnt swear to it, its a good bet that they save a cent or two this way.

Yep, that's very interesting!

Reversing the polarity of the start winding with respect to the main winding is still the way to reverse the motor direction regardless of whether you find a start cap or not. The winding resistance should identify two pairs of wires with the higher resistance being the start winding.
But again, I don't profess to be an expert ;-)

Originally Posted by Darren_111

Reversing the polarity of the start winding with respect to the main winding is still the way to reverse the motor direction regardless of whether you find a start cap or not. ....

Lets start with a warning "be careful as electricity bites - you are responsible for anything it does to you while working with electricity - not me/ubeut or anyone else!"

Now I Agree with the elegantly simple statement above

The reason for writing is to attempt to address why a single phase induction motor can be reversed --:

It comes down to what has to be achieved:

For an induction motor to work, there needs to be a rotating magnetic field. The armature simply follows it (Ok there is more to it than that but ..)


For a coil the voltage results in a current that is behind or lags the voltage.
The current results in a magnetic field.

So for a current waveform in a single coil as below :

Code:

                   _______                           ______
                /               \                     /            \ 
              /                   \                 /                \ 
            /                       \             /                    \ 
--------                            ---------                        ---------

if we want to represent the magnetic field we can expect a magnet to be pointing to the north pole north as below

Code:

                         ^
    |            ^      |        ^           | 
    |       |    |      |       |    |      |
    |       V           |            V      |
    V                                        V

ie the magnetic field gets bigger and smaller, flipping directions at the point the instantaneous current is 0 .

If viewed from a stationary rotor - this is not rotating and hence the rotor has no net-force on it hence it does not move.

OK so a second coil is added, physically at right angles to the first.
BUT to make a magnetic field at the right relationship to the main winding to create the impression of the rotating magnetic field some tricks are needed to change the timing of the current. This is where the capacitor comes in or the different inductance of the start winding. A capacitor causes the current in it to lead the voltage - if it is the dominant impedance in a circuit .... very convenient as it is one way to change the timing of the magnetic field. Once the motor is running the rotation of the rotor means the main winding is enough to keep things going as relative to the rotor the back and forth magnetic field from the stator is rotating and hence keeps the rotor going! -- having the capacitance dominant means the start winding is likely to be low inductance and hence high current hence it is a good move to turn it off --- except in ceiling fans

If there is no capacitor then the trick is to make the inductance of the start winding significantly different from the main run winding (fewer turns) -- thus the lag in current is significantly different (less) --- thus we have the effect needed. The cost of different inductance is that the start winding often has high currents in it that are not sustainable --- thus it needs to be turned off in a timely manner

OK ... so to reverse the motor we need to reverse the apparent direction of the magnetic field at start-up. This is achieved by reversing the connection of the start winding (the current flows the other way in the winding). It reverses the relationship of the magnetic field between the start and run windings -- hence the magnetic field appears to rotate in the opposite direction relative the rotor and so the rotor follows it.
--

Why no such fun for 3 phase? -- the 3 phases are already out of sync -- they create a rotating magnetic field already.

--

Hi Guys.
I guess I did not give enough info. It is a very old washing machine motor. No Cap.
But I get the idea that I have to reverse the start winding wires and all should be OK.
Thanks to all who chimed in.
Kim

Each of the answers here is correct in its own way. In small motor single phase construction there are constraints. The basic is, you can not be too greedy.
So the idea of a wind with the phase reduced by reason of resistance is not on. People buy products by looking at its efficiency, Walk into any store and you will see electrical units graded by stars. People also buy by price, so a high star unit at a low price sells.
So how do you start a motor cheaply. Well you use the inductance winds as the plate of a capacitor and the insulation as capacitor insulation. In this way you can create an efficient motor that will kick start in the correct direction due to phase shift without the need of huge losses. In higher power units this will not work.
The only other means is as stated the centrifugal switch, that though is a very old and tired idea