3 Phase Similation 1

[drax]

Could someone help me with a circuit to duplicate 3 phase from 120VAC single phase. It does not have to be accurate but I would like to show some real "dummy" values for voltage and current. Can this be done. I have a small transformer that I dupe 2 voltages but being a mech . engineer not saavy enough to figure out the current or 3rd voltage leg. thanks

 

[drax]

I'm looking for something small and portable for a demo.

 

[stevenal]

Use a small 3 phase variable speed drive that can fed single phase.

 

[waross]

Google "rotary phase convertor". and 'Add a Phase".
You may feed one phase of a three phase motor with single phase. Once the motor is started it will run on one phase and generate three phase. You may start it electrically with capacitors or just give the shaft a spin and then energise it.
It depends on your budget and the intended use of the three phase.
respectfully

 

[jraef]

It does not have to be accurate but I would like to show some real "dummy" values for voltage and current.

Maybe you should explain that a little more. Stevenal's solution is by far the cheapest and most portable, but unless you have some pretty sophisticated instruments, you are not going to read anything useful of the output side of a VFD.
Waross's suggestion is going to be better than a VFD in terms of reading quasi-3 phase voltages, but portability and ease of use becomes an issue.

JRaef.com
"Engineers like to solve problems. If there are no problems handily available, they will create their own problems." Scott Adams
For the best use of Eng-Tips, please click here -> faq731-376

 

[waross]

Hi jraef;
You are echoing a concern I had about the VFD. What about a small 3 phase motor idling on the output of the VFD to smooth out the waveform. Between the VFD and the motor back EMF would this be more usable than a "bare" VFD?
Respectfully

 

[jraef]

The motor helps in terms of the choppiness, but the motor inductance does nothing for the higher frequency components in the pseudo-sine wave. So the harmonics in a VFD output wreak havoc on basic low cost DMMs, even the ones which say True RMS on them. I have one (Fluke 1587) that is designed with a low pass filter to read the output of VFDs, but not everyone is willing to spend $450 - $800 for a meter. Even the 87V, the only other one I would recommend for VFD reading, is still over $300 on sale, more than most people are willing to spend.

 

[pqsl]

An inexpensive solution was described and explained in October 2, 1975 issue of "Plant Engineering". Components you need are:
1 - Variable transformer (could be omitted)
1 - Step-up transformer
2 - Fixed value capacitors
2 - Variable resistors or rheostats

Article was written by Robert C. Davey
"How To Get Three-Phase Power from Singe-Phase Supply."

 

[faulkma]

pqsl,

Do you have a copy of this article by any chance?, I check the net but even the archieves available do not go that far.

thanks

 

[pqsl]

faulkma,

No problem there. But I do know how to send or post the file. Maybe some one in this forum knows how.

 

[itsmoked]

Take a look at this.

faq238-1161

Stop at the point that you post them in here as images - instead just paste the links in here.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[pqsl]

Thanks itsmoked.

http://i1.tinypic.com/2vsiuiw.jpg

http://i1.tinypic.com/4i4mowp.jpg

http://i6.tinypic.com/2lkfvqd.jpg

http://i10.tinypic.com/2hrialw.jpg

If you built this. Please let us know how it worked out for you.
I will also be intrested to hear any comments on this design.

 

[waross]

One caution. When you start varying voltages on a transformer, the KVA rating is no longer valid. You must calculate the full load current based on the rated KVA and be carefull not to exceed this value of current. The KVA rating of a transformer used at other than rated voltage is the allowable full load current times the actual voltage.
respectfully

 

[itsmoked]

pqsl; No problem.. And good job!

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com