Domestic single phase to 3 phase advice please

If the one in the photo extended it would raise the bed of the sewing machine off the table. The other one would push a bar which isn't connected to anything. The must be something to do with the way the box of tricks controls the sewing/stitching but I've no idea what that might be.

I've picked up a single phase clutch motor to get me going until until I can resolve the issue with the original motor. The problem with this one is that it rotates the wrong way. The plate indicates that the rotation can be changed (cambio rotazione = exchange rotation) ...

At the moment it seems to be connected as per the diagram on the right of the plate (rotate image clockwise - the slot is at the top).

Presumably I simply change the way the brass jumper bars are connected to match the diagram on the left side of the plate?
But how do I know the positive and negative AC supply is connected correctly? This was how it came and it runs fine like this but there is no indication on the back plate to indicate which terminal is +ve & -ve.
Don't worry, when I connect it all up properly the terminals will be crimped and insulated!
I've looked online but can't find any instructions for this motor.
Many thanks in advance.
Joe

AC doesn't have + & -
The supply is connected to the same terminals - as marked "L" on the diagram. In general, it doesn't matter which way round the supply is connected.

What moving the links does is to reverse one of the windings relative to the other. This reverses the direction of rotation of the magnetic field.

BTW, the socket is for a work lamp and taps off the main winding - which is used as an auto-transformer for that.

Sorry, should have said "live" & "neutral".
So all I need to do then is swap the jumpers over as per the diagram on the plate?
Thanks for the tip on the light socket.

Here is a photo of the connector box on the 3-phase motor...

This looks far too complicated for me to attempt doing anything with safely so I'm going to abandon this motor and run the machine with the single phase motor I picked up last week. That one runs very smoothly...

The motor is spinning at 2800rpm and the pound coin in the picture is perfectly steady.

Many thanks to everyone for contributing to this thread and trying to help me out.

I've now been given another old single phase clutch motor which I'll make the subject of a separate thread. This one could be even better than the Moretti if I can just get the confusing wiring sorted out.

BotleyBouy said:

Here is a photo of the connector box on the 3-phase motor...
View attachment 178856

Click to expand...

Where does the black cable on the upper right go to ? I could hazard a guess that it's picking up 240V for the controls using the star point as a synthetic neutral.
Apart from that, "standard" star wiring. The supply comes in the bottom and connects to the ends of 3 windings - the purple, green, and orange wires at the top. The other ends of the windings (white/purple, white/green, and white/orange) are connected together as the star point.
Running it in delta on 240V is simply a matter of re-connecting the windings purple and white/orange to A;, green and white/purple to B; and orange and white/green to C; where A, B, C are the three phase connections. You can then run it off one of the .75kW VFDs you linked to early on (avoiding the unbranded one from China), or probably get away with just adding a capacitor and running it directly off the 240V single phase mains.

This looks far too complicated for me to attempt doing anything with safely so I'm going to abandon this motor and run the machine with the single phase motor I picked up last week.

Click to expand...

As above, it's actually very simple But if you've picked up an alternative motor that does the job then I guess you don't need the "complication" of generating 3 phase.

Many thanks but I know my shortcomings. I've learnt the hard way that enthusiasm is no substitute for competence

SimonH2 said:

Where does the black cable on the upper right go to ? I could hazard a guess that it's picking up 240V for the controls using the star point as a synthetic neutral.
Apart from that, "standard" star wiring. The supply comes in the bottom and connects to the ends of 3 windings - the purple, green, and orange wires at the top. The other ends of the windings (white/purple, white/green, and white/orange) are connected together as the star point.
Running it in delta on 240V is simply a matter of re-connecting the windings purple and white/orange to A;, green and white/purple to B; and orange and white/green to C; where A, B, C are the three phase connections. You can then run it off one of the .75kW VFDs you linked to early on (avoiding the unbranded one from China), or probably get away with just adding a capacitor and running it directly off the 240V single phase mains.

As above, it's actually very simple But if you've picked up an alternative motor that does the job then I guess you don't need the "complication" of generating 3 phase.

Click to expand...

As it turns out, although the the clutch motor is very good it isn't as controllable as the Efka so I'd like to give your suggestion a go. The black cable goes to the speed/sewing control box. The wires to the motor go through a hole in the motor casing behind the black connector block.

Can you tell me what rating capacitor I use please?

I'll test this outside first! Is there any risk of damaging my domestic supply if I get something wrong? The out side supply runs through a second contact breaker box to protect the distribution box in the house.

Thank you.

This photo shows the supply coming in to (from L to R) - L1 (blue), L2 (brown) & L3 (black).

The 3-phase supply to the motor is taken from terminals marked (from L to R) 1-yellow, 2-green, 3-purple, 4-white/yellow & white/green & white/purple (& brown live to the control box). In your explanation does A=1,B=2 & C=3 ?

Do I connect my single phase 240V supply L1 to blue & L2 to brown leaving L3 redundant?

In this photo I’ve removed the 3-phase supply and disconnected the live & neutral wires to the control box to simplify things.

I don’t have an orange or a white/orange so I assume that’s what the yellow & white/yellow looks like on your monitor. Would that be correct? If so then can I interpret your instructions to be :-

Yellow & white/green to 1.

Green & white/purple to 2.

Purple & white/yellow to 3.

Like this…


(Sorry, I don't know why the photo has flipped) Is this correct? If it is then to where to I connect the capacitor and what mF rating do I use? I have an 8mF (450V) would that do? Presumably one side goes to '4' but which terminal does the other side go to? And which is which? One terminal on the capacitor had a red mark, the other a black mark.

…..probably get away with just adding a capacitor and running it directly off the 240V single phase mains.

Click to expand...

It’s the “probably” bit I’m uncomfortable with.

Many thanks for your patience.

Yes, you now have it wired for delta.
The supply is connected to ANY 2 terminals out of L1, L2, L3 - but lets say you use L1 and L2.
The capacitor connects between one of those (choice determines direction of rotation) and L3.

Without the capacitor, the winding between L1 and L2 creates a strong field, and the other two windings create a weaker field that is in phase. Inside the stator, that means a field that simply flips back and forth with no rotational component. This is just the same as a single phase motor without a start winding connected. If you were to spin the motor up and then apply power, it would run (just not very well) - this is something I've done in the past (very carefully ) to test that a problem was just the start circuit.
The capacitor creates an out of phase current in two of the windings (those connected to the L3 terminal) and so creates a rotational element to the field inside the motor.

Selection of capacitor. To start with, it must be a run capacitor - continuously rated and not less than 240V AC. Many capacitors are DC and will simply explode if connected to AC - and trust me, an exploding electrolytic capacitor is an "interesting sight" even for a tiny one (I'd not like to be near a big one ). It's a matter of trying different sizes until you get the currents through the windings as balanced as you can. I don't know if there are any rules of thumb - I've only done it by trial and error (more error )
Adding some capacitance between L1 and L2 will probably reduce supply current by compensating for the reactive power factor drawn by the motor - but don't worry about that.

Had to go back and check as I'm following more than one thread involving motors. As you are starting under no load, you may be able to get away without any special starting arrangements - you are only starting up the inertia of the motor without trying to start any load at the same time. If you were starting under load then you'd need extra capacitance during starting.
This video will give you some idea about what you are building - except that what this guy calls the pony motor is your sewing machine motor. Just be aware that some of his working practices are "poor" and of questionable safety What he refers to as a "potential relay" is what would also be known as a voltage sensitive relay.

Thank you. In this photo I've connected the 240V supply and the live and neutral supply to the control box.

Originally the live (brown) wire to the control box was connected to terminal 4 but as that's now redundant it seemed logical to connect it to L2/2 as that is the live supply. Is that correct?

This is the capacitor I have...

It's rated for 450V (550V surge) but it seems too small physically for the job. It probably came out of a small bench grinder. It is 55mm long x 25mm dia whereas the capacitor on that old clutch motor I have is 100mm x50mm and rated 10mF. How important is physical size in the choice of capacitor?

Update: I connected this capacitor...

Across L2-L3 like this...


The motor started instantly and ran smoothly without overheating. The capacitor stayed cold. The voltages across the terminal were:-

L1/L2 - 230V
L2/L3 - 245V
L1/L3 - 235V

So fairly close but what is the tolerance when trying to balance the current?

The problem I now have is that the electromagnetic clutch isn't working. Really annoying as it was working perfectly before I took it off the sewing machine and the fine control it gave was the reason for the conversion exercise. Back to the drawing board!

Many thanks again for your help. I'm learning a lot.

You need power to the controls for the clutch to work. I suspect the wire connected between one of the phases and terminal 4 was the power supply for the controls.
You can either connect it between L1 & L2 (your 240V input) or a separate supply.

See the photo above, terminals 1 & 2. The brown & blue wires (top right) go to the control box and the electromagnetic clutch. I think there is a fault on the circuit board.