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# Thread: Rotary Phase Converter (Create 3-phase power from a single phase source)

1. Originally Posted by Junker2
Mr old kodger,

Please explain how you intend to connect this 240 primary to 480 secondary center tapped transformer to a 240/415 volt motor. Specifically how do you plan to wire the motor (240 volt delta or 415 volt star)?

Thanks
As I said, YOU DON'T LISTEN, "(240 volt delta or 415 volt star)?" 240 volt STAR, 415 volt DELTA! And it would seem from your question that you don't know much about electric motors either, so I will presume to teach my granny how to suck eggs.
Star connected motors have three legs each having L1,L2,L3, (in Australia, 240volts each) the common neutral for all three legs is the central star point.
I have no idea how motors are wound in America, but I can see no reason why they would be any different to Australia except to allow for the different potential .
Each winding is center tapped, the tap is the end point of the three legs (L1,L2,L3). In "star" the other ends are connected together to form the center point, giving tree pairs of windings, each pair being in parallel, and individual winding being rated for the incoming voltage (240)
In delta the center taps are still the L1,L2,L3 connections, but the other ends, instead of being connected to a common point, each individual half of a winding (still rated for 240 volts), is connected to half of an adjacent winding giving three windings comprising two individual components rated at 240 volts but in series thereby achieving a rating of 480 volts between any two center taps (it happens that two 240 volt phases, 120 degrees apart will give rise to a voltage between them of 415, but that is not relevant to the question).
It can be seen from the foregoing that a 240/480 volt transformer, center tapped on it's secondary, will effectively give two 240 volt legs 180 degrees apart relative to the center tap. I readily concede that, that will only energize one phase of a delta connected motor, but used exactly as your L1 and L2, using the center tap as the star point will energize two legs.
Now Mr Junkers2, my time is not free, so if you would be kind enough to send me a cheque for \$50 for that piece of education, it would be much appreciated.

Regards,
Old Kodger.

2. Originally Posted by old kodger
As I said, YOU DON'T LISTEN, "(240 volt delta or 415 volt star)?" 240 volt STAR, 415 volt DELTA! And it would seem from your question that you don't know much about electric motors either, so I will presume to teach my granny how to suck eggs.
Star connected motors have three legs each having L1,L2,L3, (in Australia, 240volts each) the common neutral for all three legs is the central star point.
I have no idea how motors are wound in America, but I can see no reason why they would be any different to Australia except to allow for the different potential .
Each winding is center tapped, the tap is the end point of the three legs (L1,L2,L3). In "star" the other ends are connected together to form the center point, giving tree pairs of windings, each pair being in parallel, and individual winding being rated for the incoming voltage (240)
In delta the center taps are still the L1,L2,L3 connections, but the other ends, instead of being connected to a common point, each individual half of a winding (still rated for 240 volts), is connected to half of an adjacent winding giving three windings comprising two individual components rated at 240 volts but in series thereby achieving a rating of 480 volts between any two center taps (it happens that two 240 volt phases, 120 degrees apart will give rise to a voltage between them of 415, but that is not relevant to the question).
It can be seen from the foregoing that a 240/480 volt transformer, center tapped on it's secondary, will effectively give two 240 volt legs 180 degrees apart relative to the center tap. I readily concede that, that will only energize one phase of a delta connected motor, but used exactly as your L1 and L2, using the center tap as the star point will energize two legs.
Now Mr Junkers2, my time is not free, so if you would be kind enough to send me a cheque for \$50 for that piece of education, it would be much appreciated.

Regards,
Old Kodger.

Regards
NHEngineer

3. Originally Posted by old kodger
As I said, YOU DON'T LISTEN, "(240 volt delta or 415 volt star)?" 240 volt STAR, 415 volt DELTA! And it would seem from your question that you don't know much about electric motors either, so I will presume to teach my granny how to suck eggs.
Star connected motors have three legs each having L1,L2,L3, (in Australia, 240volts each) the common neutral for all three legs is the central star point.
I have no idea how motors are wound in America, but I can see no reason why they would be any different to Australia except to allow for the different potential .
Each winding is center tapped, the tap is the end point of the three legs (L1,L2,L3). In "star" the other ends are connected together to form the center point, giving tree pairs of windings, each pair being in parallel, and individual winding being rated for the incoming voltage (240)
In delta the center taps are still the L1,L2,L3 connections, but the other ends, instead of being connected to a common point, each individual half of a winding (still rated for 240 volts), is connected to half of an adjacent winding giving three windings comprising two individual components rated at 240 volts but in series thereby achieving a rating of 480 volts between any two center taps (it happens that two 240 volt phases, 120 degrees apart will give rise to a voltage between them of 415, but that is not relevant to the question).
It can be seen from the foregoing that a 240/480 volt transformer, center tapped on it's secondary, will effectively give two 240 volt legs 180 degrees apart relative to the center tap. I readily concede that, that will only energize one phase of a delta connected motor, but used exactly as your L1 and L2, using the center tap as the star point will energize two legs.
Now Mr Junkers2, my time is not free, so if you would be kind enough to send me a cheque for \$50 for that piece of education, it would be much appreciated.

Regards,
Old Kodger.
Rob,

Did you want that check in US\$ or A\$?

4. NHengineer,

Since I think that it would take the skills of Harry Potter to materialize it, I suspect that the currency is irrelevant.

Old Kodger.

5. Originally Posted by old kodger
As I said, YOU DON'T LISTEN, "(240 volt delta or 415 volt star)?" 240 volt STAR, 415 volt DELTA!
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Regards,
Old Kodger.
Are you telling me you have a three phase motor that has a nameplate rating of 240/415 volts and a connection diagram that shows 240 volt star and 415 volt delta?

Just wondering
Junker2

6. No He is telling you that the 3 ph motors are 415 volt there are no 240 3ph motors where he is he has a single 240 hot wire and a neutral for his service.

7. Then how does he plan on connecting the center tap of the step up transformer to the center point connection of the star wired motor?

8. Originally Posted by Junker2
Then how does he plan on connecting the center tap of the step up transformer to the center point connection of the star wired motor?
He wouldn't the center tap of the secondaries would be grounded to earth leaving 2 hot wires each having 240 volts or most probably 230v with those he could connect to 2 legs of the 3ph idler motor, and connect his load to all 3 of the legs. A bank of capacitors would help to smooth out the 3 ph out put but not entirely necessary if he has a fractional hp single ph motor to spin up the idler motor.
Where the rub is a step up transformer of the size he would need is expensive in AU. However He could simply get a 35 to 40 KG spool of #9 smooth fence wire with at least a 200 mm center hole, to serve as a toridal core strip out the field winding's of several old motors use the 2 turns per volt theory and wind his own toridal transformer winding the primary first then winding the secondary over it taking care to paper insulate each layer and pulling a loop out at the center of his total winding count of the secondary for the center tap. He might have to wind 3 or 4 or even more of the cooper wire in parallel to achieve enough current carrying capacity but do able and can be economical.
If I were going to do this I would first construct a small scale version to be able to determine how large of a core and wire I would need for the big transformer.

9. Frank S,
Thank you for that information. It didn't cross my mind to wind my own tranny because I've never had to do it, but it's certainly worth a try.
Regards,
rob.

10. That's not how old kodger described the connection scheme between the transformer and the idler motor in post #147:

Originally Posted by old kodger
Junker2,
The reason you can't make it seem to work, is because your circuit schematic is wrong.
The ground between the two 240 volt "phases" should be connected to the junction point of the star. What you are trying to do is connect the circuit up delta, and you can only do that with a rotating supply (genuine 3 phase 120 degrees displaced), at which point you will find 415 between any two phases.

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