Simplest way to generate 3-phase for test bench?

[iXod]

The second link I sent above is a rotary converter, available off the shelf....

Thanks CWOW, but the request was to Jeroen3. I'd like to know what he is using.

Cheers.

[Jeroen3]

Well, my company deals in overhauling synchronous generators. You'll have some laying around that never got picked up, and you'll have contacts after 80+ years in business.
You then "simply" buy an motor, a vfd, and ask someone to weld a frame to put them on. Shaft-to-shaft.
Meanwhile you ask the electronics guys to build cabinet panel with banana plugs and some meters and buttons. You might also want an AVR in that panel.
Easy really, trivial for us. 

[Someone]

just call your power company and ask them for 3 phase

Rent a generator for the few days a year you really need it?

[Ian.M]

There is one issue with RPCs you need to be aware of - it is very difficult to keep them well balanced as the load changes, which means it is generally a *BAD* idea to run any electronics from the generated phase.  As the OP wants to test/repair brushless motors with an integrated electronic switched mode controller, with three phase input, he'll need decent power quality and voltage stability on the generated phase, to avoid the risk of tripping any phase-fault protection, which is going to require a very carefully tuned RPC, of a much heavier rating than would be needed for an induction motor load.  Its likely to also need ferroresonant transformer(s) to stabilise the output voltage.   

Even with excellent scrounging skills to get the parts for the RPC and voltage stabiliser, and assembling it all oneself to keep the cost down,  if you cost in all the time spent chasing parts and trouble-shooting it, an off the shelf budget three phase generator set is likely to be a better deal for occasional use.

[SeanB]

That's a rotary converter. At work we have several installed upstairs with panels on a desk for testing purposes.

I used to work where the 115VAC 400Hz 3 phase supply was provided by one. It, along with the big 28VDC 20kA supply, were in a separate 100 square meter room all on their own. It just had 2 buttons on the front panel, on and off, with all the other controls and the metering locked behind a perspex panel, so all you could do was see if it was working well by looking at the 3 meters. You could select ( if the panel was open) to see incoming phase voltages and currents on the left meter, and with the right one the outgoing using a similar switch. The middle one was just a vibratory frequency meter.

The 28VDC supply was even simpler, just a power light, power key switch, and a voltmeter and DC ammeter behind the perspex.

You might ask why a 28VDC supply capable of supplying such a ridiculously high current. It was used to test run aircraft engines in the service bay next door, which used the built in engine starter generator to turn the engine over, and using aircraft standby hydraulic pumps, which also run off the 28VDC battery supply, to provide lubrication and cooling oil for the first tests on first test run. We could also use it to start aircraft in for service, or to provide ground power during servicing. As we had typically 6 aircraft in at any time this all added up.

[iXod]

Easy really, trivial for us. 

An engineer's definition of trivial! 

Thanks!

[iXod]

...Even with excellent scrounging skills to get the parts for the RPC and voltage stabiliser, and assembling it all oneself to keep the cost down,  if you cost in all the time spent chasing parts and trouble-shooting it, an off the shelf budget three phase generator set is likely to be a better deal for occasional use.

Thanks for that perspective Ian. It's something I would gain from (bad) experience, so you save me the pain. 

By "genset" I presume you mean single-phase motor driving 3-phase gen. How does this differ from driving a 3-phase motor?

Cheers.

[Ian.M]

No, I mean a gasoline or diesel engine coupled to a three phase generator head.  Small ones are usually highly integrated with the generator bolted directly to the engine bellhousing, often without a separate bearing for that end of the generator rotor, and a control system for the throttle for frequency control, and power, and for the field current to maintain output voltage.

A motor-generator set is a different creature - single phase motor driving a generator  as Jeroen describes.

[iXod]

No, I mean a gasoline or diesel engine coupled to a three phase generator head.  ...

Right. Thanks!

[Electro Detective]

Anks and Kevman suggested using a function generator and 3 audio amplifier channels.

How does that get you 3 sine waves 120 degrees phase apart?

I am guessing even if it was feasible you would need the signal generator putting out 50hz or 60hz going into a delay unit with 3 outputs with appropriate delay times, going into each amp channel.

Anyone here want to offer the delay time math for 3 sine waves 120 degrees apart?

Then you'd need amplifiers capable of putting out 120 volts without cashing in on some magic smoke...

Forgive my skepticism   

[Jeroen3]

You use a sound card.
And you use sensing transformers in reverse.

[capt bullshot]

Anks and Kevman suggested using a function generator and 3 audio amplifier channels.

How does that get you 3 sine waves 120 degrees phase apart?

I am guessing even if it was feasible you would need the signal generator putting out 50hz or 60hz going into a delay unit with 3 outputs with appropriate delay times, going into each amp channel.

Anyone here want to offer the delay time math for 3 sine waves 120 degrees apart?

That's trivial: http://wunderkis.de/pwramp3/ (scroll down until the phase shifter)

[mikeselectricstuff]

Then you'd need amplifiers capable of putting out 120 volts without cashing in on some magic smoke...

Mains transformers, connected backwards.

[Anks]

Then you'd need amplifiers capable of putting out 120 volts without cashing in on some magic smoke...

Mains transformers, connected backwards.

cheers

[David Hess]

How does that get you 3 sine waves 120 degrees phase apart?

Either build a three stage phase shift oscillator which is an almost trivial exercise or perhaps better, filter the output from a 3 stage Johnson counter.  The digital method lends itself well to a microcontroller implementation.

3 linear power amplifiers capable of producing about a kilowatt of 3 phase power would not be fun though.  3 class-D audio amplifiers of the required power would be feasible though.

[Electro Detective]

Thank you for the replies,

"using a function generator and 3 audio amplifier channels" for a usable low to moderate current 3 phase system isn't going to happen easily, with just those items at hand.