Looking for a 3-phase output, 1-phase input AC power supply

[M1200AK]

  I'm having a hell of a time trying to find a 3-phase output, 1-phase input, AC power supply for doing a very simple PCB voltage measurement check.  The PCB needs to measure the phase to phase voltages through three separate voltage divider networks and then transfer the lower voltage signals to the DSP PCB where it will measure the frequency.

  The test procedure calls for being able to adjust the voltage between phases from 342 VAC to 550 VAC and the frequency between 50 Hz and 60 Hz.  The current requirement is negligible, limited to 10 mA actually.

  I don't need to do anything with the power supply except set it to a voltage and frequency, check that the boards report the correct values and that's it.  So I don't need an AC supply that has dozens of built in features beyond that and costs $10,000 or more USD.

  So far I've been able to narrow it down to having to purchase three ITECH IT-M7723 supplies and connecting them in parallel to create the 3-phase signal.  This will cost a total of somewhere between $4,000 to $5,000 it looks like.  https://www.itechate.com/en/product/ac-power-supply/IT-M7700.html

  Is there not a basic bench top AC power supply that can output the signals I need?  Buying three IT-M7723's seems like such an overkill for what I need them for.

  Thank you in advance for any helpful information or suggestions.

[edpalmer42]

Would a VFD, perhaps with an external filter, do the job?  ebay has a category for Variable Frequency Drives and lists almost 40K items.

[Conrad Hoffman]

I don't know how clean the VFDs are, but Automation Direct is my go-to:
https://www.automationdirect.com/adc/shopping/catalog/drives_-a-_soft_starters/ac_variable_frequency_drives_(vfd)/micro_vfds#

[_Wim_]

Use a signal generator with 3 outputs follow by some high voltage amplifier from Apex (maybe 3 evaluation boards in diy needs to be avoided?). They certainly have opamps that can output 10mA and > 400V.

[nctnico]

I'd DIY something using function generators which can be synchronised, 3 power amplifiers and 3 mains transformers (like 6V to 400V).

Edit: also 3 power amplifiers.

[langwadt]

I'd DIY something using function generators which can be synchronised, 2 power amplifiers and 3 mains transformers (like 6V to 400V).

sound card and stereo amplifier + three transformers ?

[Stray Electron]

  As you've already found out what you're asking for sounds simply in theory but very expensive in practice!  Do a search for Elgar AC Power Source on this forum, they've been discussed on here several times already and they designed to do exactly what you're asking. I posted information about one model that I have that does exactly what you're looking for; i.e. one phase in and three phase out, and I listed the exactly model number of the main unit and the control head for it.  Manuals and data sheets for them are online and USED Power Sources are available via Ebay or local .MIL surplus stores.

[pdenisowski]

I looked into this recently as well, and as far as I could tell there is no inexpensive solution for this.

A rotary converter is sometimes an option, but I'm not aware of any that allow the three phase output voltage to be adjusted.

[Martin72]

I don't know how clean the VFDs are

As you can imagine from the size, not at all.
What comes out isn't a pure sine wave—and that's not strictly necessary for a motor anyway.
In any case, a low-pass filter would have to be connected downstream to generate a sine wave.
Our VFDs have something like that built in, but they're also significantly larger.
And much more expensive. 

[langwadt]

I looked into this recently as well, and as far as I could tell there is no inexpensive solution for this.

A rotary converter is sometimes an option, but I'm not aware of any that allow the three phase output voltage to be adjusted.

from OP: " The current requirement is negligible, limited to 10 mA actually."

[mikeselectricstuff]

The smallest VFD on Aliexpress is about $40 , so may be worth looking at.
I recently ordered one for a similar application & will report back here on how useable it is.

True sinewave inverter boards are available very cheaply, and usually use a well-documented driver module. You could probably phase-lock three of these fairly easily

e.g. https://www.aliexpress.com/item/32963315163.html
Control module datasheet :
https://www.microcontroller.hu/wp-content/uploads/2025/05/egs002.pdf

maybe a sinewave brushless motor controller plus reverse-connected mains trasnsformers. These tend to have hall sensor inputs so you may need to connect a motor to keep it happy.

[mikeselectricstuff]

Use a signal generator with 3 outputs follow by some high voltage amplifier from Apex (maybe 3 evaluation boards in diy needs to be avoided?). They certainly have opamps that can output 10mA and > 400V.

Or a cheaper solution than Apex - 3 channel audio amplifier feeding step-up transformers

[langwadt]

Use a signal generator with 3 outputs follow by some high voltage amplifier from Apex (maybe 3 evaluation boards in diy needs to be avoided?). They certainly have opamps that can output 10mA and > 400V.

Or a cheaper solution than Apex - 3 channel audio amplifier feeding step-up transformers

when you need to use transformers anyway you can do it with two channels,  ph3 = - (ph1 + ph2)

[nctnico]

  I'm having a hell of a time trying to find a 3-phase output, 1-phase input, AC power supply for doing a very simple PCB voltage measurement check.  The PCB needs to measure the phase to phase voltages through three separate voltage divider networks and then transfer the lower voltage signals to the DSP PCB where it will measure the frequency.

This sound like you don't need 120 degrees between the phases. If you only measure voltage, then you could use a single source and just test the inputs 1 by 1. Or all 3 in one go.

[Stray Electron]

I looked into this recently as well, and as far as I could tell there is no inexpensive solution for this.

A rotary converter is sometimes an option, but I'm not aware of any that allow the three phase output voltage to be adjusted.

from OP: " The current requirement is negligible, limited to 10 mA actually."

   The Elgar Power Source that i pointed out in one of my earlier posts allows the output to be adjusted from 0 to 265 (IIRC) VAC and allows some range of adjustment between the output phases. But it is also capable of much greater that 10ma amperage (they're actually limited by the output Power and not strictly amperage).  But I'm not aware of anything else that has similar capabilities but  only outputs anywhere near as low as 10 ma.   Someone else may make a source with a lower power output but you would probably have to buy a New one and it's probably going to be a special order item. The Elgar sources in the 250 watt to 1000 watt output  range are widely used for testing high grade commercail aircraft and .MIL equipment so you can find them used for a fraction of their original costs.

   Trying to find a source that only supplies 10ma or so of output is going to be significantly harder than finding one that outputs somewhere in the up to 5 amp range.

[Doctorandus_P]

What about the good old mechanical method?

Get a BLDC motor (Those are good generators because they have permanent magnets, and then drive the motor with another motor to control it's speed.

Stepping up the voltage can be done easily with a few transformers. For example: Take two 230Vac to 12V transformers for each motor phase, then connect the 12V sides in parallel to the motor/generator, and put the 230Vac sides of the transformers in series.

Some ideas: "universal" transformers with many taps help with adjusting the relation to output voltage and frequency. You can use some rheostats (old fashioned power potentiometers) to add more adjustability.

[Martin72]

To address the topic of three-phase generators:
We’ve been using something like this for 30 years because there wasn’t a ready-made solution back then (we needed frequencies higher than 50–400 Hz).
So we built our own three-phase sine wave generator back then—and used it to drive three PA power amplifiers...
It still works perfectly to this day.
I can’t reveal exactly how it’s built, but—as you might expect—you can now get a three-phase sine wave generator cheaply from Asian suppliers:

https://www.ebay.com/itm/285817496313

A “prettier” version:

HS384

Then there's the same thing, only controllable via USB and so on.
So, just get an amplifier, and you're all set.
Anyone interested in exploring this topic might be interested in GW Intek's evaluation board:
https://www.gwinstek.com/en-global/products/detail/PEK-130

Manual with circuit diagrams:

https://www.gwinstek.com/en-global/products/downloadSeriesDownNew/14564/1793

[pdenisowski]

but—as you might expect—you can now get a three-phase sine wave generator cheaply from Asian suppliers:

If you simply want a three channel / phase function generator as a "box", those do exist - I have one ("FeelElec FY8300S") and although it feels like a toy, it works fine.

Since current requirements are so low, I suppose it might be possible to take the outputs and step them up to the voltages you need - I've done this (12V to 120V) using three cheap doorbell transformers.  By controlling the (low) input voltage to the transformers, you could then control the (high) output voltage.  (Just an idea - lots of "details" to work through  )

[Martin72]

Based on this idea, I once built a test device that allowed me to test control cards individually by simulating control loops with it.
Since their inputs had high impedance (meaning they required little current), measurement transformers were sufficient for me to step up or step down the respective output voltages (115V, 230V, 440V).
When stepping up the required voltages, care must be taken to ensure that the source can drive the low-impedance secondary terminal of the transformer.
But that should be obvious to everyone.

[woody]

If you simply want a three channel / phase function generator as a "box", those do exist - I have one ("FeelElec FY8300S") and although it feels like a toy, it works fine.

Too funny to let it pass 🤣

[jjoonathan]

> Warfoam Generator

If only the NNSA had this back when when they forgot how to make the thermonuclear styrofoam, they could have saved $100M!

[pdenisowski]

If you simply want a three channel / phase function generator as a "box", those do exist - I have one ("FeelElec FY8300S") and although it feels like a toy, it works fine.

Too funny to let it pass 🤣

    Surprised it isn't ITAR restricted

I've been working in T&M for ~ 30 years and I have never seen a box as cheaply constructed as this one: it feels like an empty plastic case and the controls are about as non-intuitive as you can get.  But it does output three relatively stable phase coherent (but shiftable) sinewaves, which is all I needed it for.