Three phase from single phase

[Humble2000]

I am looking for a device to generate three phase signal from a single phase transformer. I appreciate any feedback on this.

 

[waross]

We need a little more information.
Power?
Signal?
Run a motor?
Run some other device?


Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[Humble2000]

I need this to create low power signal for a controller that I have. So power will be less than 50Va at 6V.
Suppose I have a 120/6V transformer 50VA, how can I generate a three phase signal from this XFMR.
I beleive power will be divided by three now.

 

[waross]

For a signal level supply, you may design an RC circuit that causes a 60 degree phase shift. Then reverse the polarity to get the 120 degree phase shift of three phase.
Add an RL circuit to develop a 60 degree phase shift of the opposite rotation. Again reverse the polarity for the 120 degree shift of the third phase.
small power levels of three phase may be generated by a Roto-Phase. This is a three phase motor started and run on single phase with the aid of capacitors. Once started a three phase motor will continue to run on one phase. It acts as an induction generator and three phase power may be supplied from the three motor line terminals.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[jraef]

So just to be clear, you need 6V 3 phase power then? And you have a 120V single phase source?


"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
For the best use of Eng-Tips, please click here -> faq731-376

 

[Humble2000]

Jraef...Yes Thats correct.
I thought there must be a commercial unit available by now to do this kind of conversaions..something that you input single phase and you get three phase out. Motor will be too big.I need sth. that I can use in a small box.

 

[VEBill]

Instead of thinking about converting the 1-phase input to 3-phase output, start to think in terms of just creating the 3-phase signal from scratch with a bespoke 3-phase generator circuit. Just use the 1-phase input for power, and for timing the generator clock to phase-lock the output to the input (if necessary).

With this approach, all you need is a power supply circuit and a 3-phase generator circuit.

 

[Humble2000]

I need something small. I think I have to go with Warros suggestion. I was under impression that I can get a simple box to do the thrick,it seems most of converters are with motors or unsing power electronics to convert 1-phase to 3-phase!

 

[MacGyverS2000]

What do you intend to drive with this circuit? What is the purpose?

Dan - Owner

http://www.Hi-TecDesigns.com

 

[ScottyUK]

Some good ideas in this thread240-210859 which would expand to a 3-phase solution quite easily.


----------------------------------

If we learn from our mistakes I'm getting a great education!

 

[jimkirk]

Rectify, filter & regulate (switch mode supply) the output from your 6 volt transformer. Use a PIC or similar micro to generate three appropriate PWM outputs driving three MOSFET push-pull output stages with appropriate filtering of the output. Small and efficient with crystal controlled output frequency. I'm sure there's a way to synchronize to your mains frequency if necessary.

 

[OperaHouse]

I don't think 50VA three phase is such a small request. I have a couple 100W three phase generators and they are neither small or cheap. Even on ebay you will spend quite a bit. The RC phase shift is easy to do and then add three (maybe just two) IC power amplifiers. The trouble with the RC shift is that the angle will change with frequency. Do you really need 50W or is this just a random figure you threw out? That is a sizable current at 6V.

 

[ScottyUK]

Generate the three sines digitally. Analogue methods aren't impossible but it sure is entertaining trying to prove that it can be done.


----------------------------------

If we learn from our mistakes I'm getting a great education!

 

[Humble2000]

ScottyUK...I have spent all day trying to make the Analogue one working as suggested by "waross"
No LUCK..has anyone tried this before!!!!!!!!
Ok here is what I done...
6V secondary transformer 43VA- a 3.3micro cap + a pot.

and a 1M resistor as a load.
I cant seem to be able to vary the phase angle, even when I change the pot!!
even without the pot ,I cant get the 90 deg. phase shift that the cap is supposed to provide!, hmmmmm, any ideas?

 

[waross]

How are you measuring the phase shift?
Try this, ground the point where the resistor connects to the transformer. Use this point as the common for a two trace scope. Connect one probe across the transformer and the other probe across the resistor.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[davidbeach]

The more of this I read, the more I wonder if this isn't a wild goose chase. It would seem that any thing that small that requires 3-phase (as a controller) is looking for that 3-phase as a representation of what it is trying to control. Taking one phase from the controlled system - or even worse from elsewhere - and trying to derive two more phases won't provide meaningful input to the controller. you really just need to provide two or three transformers and provide honest to gosh three-phase voltages from the controlled system to the controller. Otherwise you will have a case of garbage in-garbage out.

 

[Humble2000]

waross,
I am using two channel scope and I am using N as a common point and CH1 connected to xfmr and CH2 after cap( On load resistor )

------/\/\/\/\ |---||----|CH2
CH1 | | |
------| |
\
/
\
/
|
N( Common) |
---------------------------

 

[davidbeach]

If you will use the [ignore]

 and

[/ignore] tags you will get a fixed pitch font and your ASCII graphics will look a whole lot better.

------/\/\/\/\   |---||----|CH2
CH1       |      |         |
           ------|         |
                           \
                           /
                           \
                           /
                           |
           N( Common)      |
---------------------------

 

[Humble2000]

Thank you.

 

[LionelHutz]

Attached is a 3-phase waveform generating circuit. It works but you have to make R2 slightly more than 2x R1 to get it to oscillate. Going exactly 2x works in theory but doesn't account for any losses in the circuit.

I'll leave it up to you to add power op-amps or other circuitry to the 3 op-amp outputs to increase the output power of the circuit if that is required.