Is this circuit viable ?

[ClydeCrashKop]

Would a capacitor type phase converter out put be like the Wild leg 3 phase?
Thinking about inductors vs. capacitors and current lagging vs. leading, what would the current timing look like on those two when applied to a motor?
I found a few pictures but not voltage vs. current on 3 phase.

 

[jeff10456]

Kool. Small world ....

 

[unclejed613]

i worked for a few years for an AM radio station, and their transmitter was literally in the middle of a cornfield. the building was supplied by a single phase power line, but the transmitter required 3-phase power (true 3-phase, or the power supplies would have too much ripple). they used a rotary converter to change the single phase power to 3-phase. that was a rather large piece of machinery.

 

[JimB]

(true 3-phase, or the power supplies would have too much ripple)

An interesting thought.

I guess the effect of using three phase would be two fold:

1 The raw rectified three phase would have inherently less ripple, the voltage never going anywhere near zero as we get when a single phase is rectified.
2 The ripple frequency would be much higher, 360Hz as against 120Hz for a single phase. (Assuming a 60Hz supply frequency).

As a result, the filter capacitors and inductor (?) in the PSU could be much smaller.

JimB

 

[jeff10456]

Would a capacitor type phase converter out put be like the Wild leg 3 phase?

A minimal amount of caps would probably look like what I call a "wild leg", enough caps of the right size could "tune" it to look like true 3 phase. I actually think your first diagram answers your question concerning true 3 phase, and of course the voltage and current values would be higher for the wild leg. Yes they only show a single phase, (probably because the 3 together on the same graph would be too crowded to read), just copy the wave forms of that graph and paste it right back on itself two times at the next 1/3 of the time cycle each (in this graph that would coincide with the 120 and 240 degree locations on the time vector) and that is what it would look like. I don't understand the next two graphs, mostly because they are using voltage terms that I simply don't know/understand/am not familiar with.
Another thing that confuses me is realizing/remembering that when UK members refer to 230V single phase they are talking about a hot and neutral. When US members refer to 230V single phase they are talking two hots and maybe a neutral. It is interesting to me that they can make a 3 phase motor run on their voltage, what US members would relate to as 120V.

 

[jeff10456]

i worked for a few years for an AM radio station, and their transmitter was literally in the middle of a cornfield. the building was supplied by a single phase power line, but the transmitter required 3-phase power (true 3-phase, or the power supplies would have too much ripple). they used a rotary converter to change the single phase power to 3-phase. that was a rather large piece of machinery.

Do you know what was the output voltage for each leg to ground/neutral of the converter? Do you have or can you get or draw a schematic of it?

 

[Ylli]

Rotary converter =? motor/generator

 

[jeff10456]

Interesting, I haven't heard of a wild leg since I was in Louisiana.

I finally remembered that the utility linemen and engineers called it an "Open Delta" configuration, as opposed to a normal/closed delta configuration for true 3 phase

 

[jeff10456]

Rotary converter =? motor/generator

to answer your question there are several kinds of Rotary Phase Converters (they are not generators)
go here and read all of the thread if you want to learn about them.
https://www.electro-tech-online.com/threads/3-phase-converter-schematic-miller-system.100563/
when you get to the 8th page you will see where I was directed to another forum and thread, if you are still interested follow that link and read all of it.
By that time you will have learned enough to build your own if you choose

 

[jeff10456]

Would such thing work?

If you are really interested ....
go here and read all of the thread if you want to learn about running 3 phase motors from single phase power.
https://www.electro-tech-online.com/threads/3-phase-converter-schematic-miller-system.100563/
when you get to the 8th page you will see where I was directed to another forum and thread, if you are still interested follow that link and read all of it.
By that time you will have learned enough to build your own if you choose, and to answer other peoples questions.

 

[jeff10456]

I have been using the "Top Secret Recipe" for decades on motors up to 10 HP

Do you know what the volts and amps per leg are for this circuit? any HP you have available for this data will be Very helpful.
Thanx,
Jeff

 

[ClydeCrashKop]

The only one I could measure easily is a 10 HP on my lathe. It was 248 to 250 volts across all legs. I can't see the actual cap markings because they are neatly bundled.

For a 2 HP motor they would be 30 uF oil caps for the run circuit and 300 uF electrolytic caps for the start circuit.

The tolerance is +/- 7.5 uF on the oil caps for the run circuit and +/- 75 uF on the electrolytic caps for the start circuit so get as close as you can with standard denomination caps.