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

[smithdoor]

I would look at a buck and boost transformer The machine tool may need the adjustment too. They are 50Hz too

Dave

Ah so, this situation is not unique to Australia then. That means my design will not work for any British Crown Colony location and GB itself. I'll see if I can find a work around.

[nhengineer]

I would look at a buck and boost transformer The machine tool may need the adjustment too. They are 50Hz too.
Dave

If the idler motor is 50Hz then its output will also be 50Hz. By the way, a 3-phase 50Hz motor is quite happy to run on 60Hz 3-phase. It will turn about 1.2 * faster than that which is written on its nameplate however.

I'm wondering, Dave, what will be accomplished with a buck/boost transformer? The issue here is most former United Kingdom locations are 220 (230 now actually) with a single hot lead and a neutral. In order for my present design to work, there needs to be two hot leads (out of phase with each other) with reference to earth ground.

[smithdoor]

Yes they change the voltage starting 1980's was switching from 240 to 230 volts it was a 20 year plan with a low limit of 216 to high limit of 253 volts. This at the meter
If you have long run from the meter to tool you then have a greater drop
So if need to adjust for a motor it simple with a buck and boost

As far as 50 Hz to 60 Hz
The tools I had it past that had 50Hz motor I just ran tools for 20 year or more on 60Hz be for selling the tools working great on 60Hz. Some castes I replace the pulley with smaller one so RPM plate was right.

Dave

[Marc Broussard]

Hi. Three phase motors are very cheap. The junk yards sell them for scrap price here. I have a 7 1/2 HP they sold me for 14$. And most single phase motors 1/2 hp or bigger will spin a big 3-ph one. I have all the components to build one right now but, if I use my 3-ph motor for a converter I won't have anything 3-ph to run. Go figger.

[smithdoor]

Sound like it will work
Do you photos or drawing you post
If you using a three-phase motor as you converter it is working as a generator making as some call the third leg

Dave

Hi. Three phase motors are very cheap. The junk yards sell them for scrap price here. I have a 7 1/2 HP they sold me for 14$. And most single phase motors 1/2 hp or bigger will spin a big 3-ph one. I have all the components to build one right now but, if I use my 3-ph motor for a converter I won't have anything 3-ph to run. Go figger.

[Frank S]

My rotary phase converter is kind of small actually too small in some ways,being only a 3 Hp it is started by the use of 3 large capacitors with no small spin up motor. I really need to build a larger one with a spin up motor but it came with my lathe when I bought it and has been running it for a few years even though my lathe is 4 hp, as long as I don't try to make a .200" cut @ .015" feed it does just fine any heavier cut and it will bog down.Also I have found that if I switch on my 3 Hp mill and just allow the motor to run without any work being done then the lathe do a little better when starting it or reversing it.
I an thinking that when I build a larger converter I will use a 1/2 or 3/4 Hp spin up motor direct coupled to a 7.5 or 10 Hp motor with a large flywheel to help with the higher current load my 450 Amp mig welder will require

[smithdoor]

They not hard to build
I have simple drawing just using a AC potential relay and starting capacitor

Here is the drawing

Dave

My rotary phase converter is kind of small actually too small in some ways,being only a 3 Hp it is started by the use of 3 large capacitors with no small spin up motor. I really need to build a larger one with a spin up motor but it came with my lathe when I bought it and has been running it for a few years even though my lathe is 4 hp, as long as I don't try to make a .200" cut @ .015" feed it does just fine any heavier cut and it will bog down.Also I have found that if I switch on my 3 Hp mill and just allow the motor to run without any work being done then the lathe do a little better when starting it or reversing it.
I an thinking that when I build a larger converter I will use a 1/2 or 3/4 Hp spin up motor direct coupled to a 7.5 or 10 Hp motor with a large flywheel to help with the higher current load my 450 Amp mig welder will require

[Paul Alciatore]

I do not have a copy of nhengineer's plans, but using them with 220V, single phase power should be possible. The 220V supply with one end grounded can be easily passed through a 1:1 transformer with a center tapped secondary. Then that center tap on the secondary would be connected to ground and you instantly have the exact same "two phase" dual 110V supply lines as are used in the US. The transformer would need to be sized properly for the load current, but it should work just fine. I would expect for it to cost a bit, probably more than the junk yard three phase motors, as it would be a more useful item.

As an alternative, you could use two step down transformers that each produce 110V on their secondaries and connect those secondaries in series with that common connection grounded. That is exactly the same thing electrically and those may be easier to find. If you are in doubt about the series connection of the secondaries, you only need to measure the Voltages. If they each produce 110V and you measure 220V across the two in series, then the connection is correct. But do this before connecting any load circuitry.

Note: I know my use of the term "two phase" above is unconventional. But, IMHO, it does accurately describe the household power here in the US. There are two separate Voltages and they are 180 degrees apart so they ARE two distinct phases. The problems discussed in this thread strongly support that use of the terminology. But I do understand why, here in the US, it is referred to as single phase. That is because it is derived from a single phase of the three phase lines that are used for the transmission of that power from the generating plants to our neighborhoods. It is only in a transformer that sits on a pole that is within a few thousand feet of a home or other user that it is converted from a single phase, 5KV or 10KV line to the 120V-G-120V configuration that we all use. I do like to think of those pole transformers as single phase to two phase converters. And BTW, those pole transformers are just larger versions of the center tapped transformer that I am suggesting that you can add in other countries where single phase power is really just that, SINGLE PHASE. Electrically there is absolutely no difference.

So please don't jump on me for using the term "two phase" for US power. PLEASE! I have been through it before.

[old kodger]

Hi Paul,
I had been thinking about a 230-0-230 volt transformer arrangement such as is used in electronic circuit supplies (usually 25-0-25 for medium output amplifiers), however, as you point out, the phases are in fact 180 degrees out of phase not 120 and I did wonder how that would effect the performance of the motor, in that it would "confuse" the third phase orientation.

Regards,

Rob.

[smithdoor]

No this does not work this only 180 deg you need either 90 (2 phase) or 120 deg (3 phase)
Even single phase motors cap start has 2 phase winding for starting
I think most of wish that wood work too.

Dave

I do not have a copy of nhengineer's plans, but using them with 220V, single phase power should be possible. The 220V supply with one end grounded can be easily passed through a 1:1 transformer with a center tapped secondary. Then that center tap on the secondary would be connected to ground and you instantly have the exact same "two phase" dual 110V supply lines as are used in the US. The transformer would need to be sized properly for the load current, but it should work just fine. I would expect for it to cost a bit, probably more than the junk yard three phase motors, as it would be a more useful item.

As an alternative, you could use two step down transformers that each produce 110V on their secondaries and connect those secondaries in series with that common connection grounded. That is exactly the same thing electrically and those may be easier to find. If you are in doubt about the series connection of the secondaries, you only need to measure the Voltages. If they each produce 110V and you measure 220V across the two in series, then the connection is correct. But do this before connecting any load circuitry.

Note: I know my use of the term "two phase" above is unconventional. But, IMHO, it does accurately describe the household power here in the US. There are two separate Voltages and they are 180 degrees apart so they ARE two distinct phases. The problems discussed in this thread strongly support that use of the terminology. But I do understand why, here in the US, it is referred to as single phase. That is because it is derived from a single phase of the three phase lines that are used for the transmission of that power from the generating plants to our neighborhoods. It is only in a transformer that sits on a pole that is within a few thousand feet of a home or other user that it is converted from a single phase, 5KV or 10KV line to the 120V-G-120V configuration that we all use. I do like to think of those pole transformers as single phase to two phase converters. And BTW, those pole transformers are just larger versions of the center tapped transformer that I am suggesting that you can add in other countries where single phase power is really just that, SINGLE PHASE. Electrically there is absolutely no difference.

So please don't jump on me for using the term "two phase" for US power. PLEASE! I have been through it before.