changing a 3 phase motor to single phase

[DIYedboy]

Before we start, I don't have a motor to do, (I'm just interested in how it's done). I understand that two of the windings must be wired in series and the other needs a capacitor added.

Tell me more oh wise and fully experienced ones..........................

 

[plugwash]

You need to have access to both ends of all three windings to do it.

Two windings are connected in paralell to make one big main winding. The third winding is conencted in series with a capacitor and acts as a start winding.

 

[TicklyT]

3 phase motors are designed to run on three phases at 120 degrees to each other.

Simply adapting a motor means it will usually end up down on power, overheating and vibrating. Two of the 'phases' would be at 180 degrees (they are really the same phase connected opposite ways round to two of the windings). The third 'phase' ends up at an undefined angle and voltage, depending on the load on the motor among other things.

You would probably need to make arrangements to vary the capacitance generating your third 'phase' between starting and running states just to get the motor to start.

 

[DIYedboy]

Would it not be correct to say that a single phase motor has the live and neutral 240/120 degrees apart and the capacitor gives capacitance reactance which then creates the live and neutral at 180 degrees apart?

 

[RF Lighting]

Connect it to an invertor

 

[Spark123]

Would it not be correct to say that a single phase motor has the live and neutral 240/120 degrees apart and the capacitor gives capacitance reactance which then creates the live and neutral at 180 degrees apart?

No

Single phase live to neutral will be in phase with each other, you physically connect the coils the opposite way around to get the magnetic fluxes to be 180deg out of phase to what they should be.
A capacitor will cause current to lead voltage hence the magnetic flux which is created by the current will be out of phase to that of the supply voltage. Capacitive reactance is what limits current flow, the impedance (Xc) of an AC circuit. Xc acts at 90 degrees to a resistive circuit, Xl acts the opposite way at 90 degrees to a resistive circuit.

 

[ericmark]

I do remember many years ago when I was an apprentice seeing a donkey motor with large flywheel and capacitors which was started to create three phase from single phase and once running the other three phase motors could be added to the system.

I think the circuit diagram was in the Newton's complete engineer but my set is in garage and I can't get to them.

With the advent of electronic inverters the need for these systems went away and I have not seen one for years.

With a Google I found this Three Phase Power Solutions PDF which does show some of the methods and refers to a few old methods it seems it came from model engineer and I would think many a steam enthusiast would buy old equipment they do not seem to have moved far away from the age they want to emulate.