Simplest way to generate 3-phase for test bench?

[iXod]

Sometimes I need to diagnose/repair small 3-phase brushless blower motors with integrated SMPS motor driver PCB. Have only 120 and 240v single-phase power available.

Thought about a VFD and fixing frequency param to 60 only (yes, I'm in USA) and vary only the voltage, but as good as this sounds it's not do-able, with the VFDs I tried.

What's the simplest way to get 3-phase power? Need less than 10 amps.

Thanks.

[CatalinaWOW]

Simplest way is to buy a phase converter.  Various types and sizes are available.  Something like the following.

https://www.zoro.com/phase-a-matic-phase-converter-static-1-3-hp-pam-300hd/i/G1518142/

[kolbep]

What about Coupling a Single Phase Motor (on Speed Control), to a 3 phase motor / alternator?
Would that work

[Excavatoree]

What about Coupling a Single Phase Motor (on Speed Control), to a 3 phase motor / alternator?
Would that work

Those do work  (search for rotary phase converter)  but they are typically used for higher power applications.  Many are choosing to use electronic phase converters now that their costs are lower than they were when the rotary phase converter was popular.

My dad uses a rotary converter he cobbled up from a single phase motor and a three phase motor to power his milling machine, but it's clunky, large, and a pain in the rear.

[Jeroen3]

A small rotary converter with VFD motor basically gives you a variable Frequency and Voltage unit. 
The short circuit capacity is also limited to the flux in the generator and limit on the exciter system. Much cleaner and safer than a VFD to test motors.

However, you could also use a three phase variac. I've revised fan motors for trains as a summer job and used a three phase variac for this.
Note that a three phase variac I used then is the size of a cabinet.

[iXod]

1ph motor speed control is usually "iffy". 1ph motor (at full speed) to drive 3ph motor or alternator would work. If motor speed specs (ie, both 1750) the 3ph should output its rated voltage.

Or 1ph -> 3ph VFD driving 3ph motor driving another 3ph motor or alt. But that kinda misses the "simple" requirement...

Thanks.

[CatalinaWOW]

Define simple.  If you want cleaner 3 phase, or to have more power margin, nothing is much simpler than pulling out the credit card.

https://www.zoro.com/phase-a-matic-phase-converter-rotary-1-hp-208-240v-r-1/i/G7969981/?gclid=CLCY28nmoM4CFQGRfgodGG4HEw&gclsrc=aw.ds


I don't necessarily recommend the brands I have posted, they are just examples.  The smaller electronic converter posted earlier is under $200, the one above is under $600.  Shipping will add a fair amount.  If you are going to be using this regularly those dollar amounts seem quite reasonable.  Space would be something of an issue, particularly for the larger unit.  Any of the commercially supplied units will be relatively trouble free, unlike the set ups which bodge together a couple of motors.  Unless you are really good at mechanical work you will end up with the maintenance nightmares mentioned above.

Depending on your usage a fair amount of wiring would be appropriate, setting up a receptacle on your bench and so on, departed further from simplicity.


Another option would be to set up a toolkit with the instruments you need and then do the work at the customer site.  They obviously already have the power available.

[Anks]

Signal generator and some high power audio amplifiers may work. Crown macrotech have been used in labs and I've seen them drive a short but weather or not they can produce the voltage swing necessary to drive a motor or I've no idea.

Just an idea

[Kevman]

Simplest way is to buy a phase converter.  Various types and sizes are available.  Something like the following.

https://www.zoro.com/phase-a-matic-phase-converter-static-1-3-hp-pam-300hd/i/G1518142/

These are just caps and a time-delay-relay in a box to get the pull a line out of phase for just long enough to get the motor spinning. They don't create any phases. The motor being powered will only have 2/3 its rated power as one winding will be completely ignored during running.

They can be used with a second three phase motor, though- the other (unloaded) motor will generate the phase on its unpowered winding. Not sure that's what you want.

You can always use a function generator and 3 audio amplifier channels!

[mikeselectricstuff]

If it's a brushless with a SMPS, does it actually need to be supplied AC?

[iXod]

If it's a brushless with a SMPS, does it actually need to be supplied AC?

You're thinking 240vdc? (c;

Thanks.

[iXod]

I'm liking this:

[mikeselectricstuff]

If it's a brushless with a SMPS, does it actually need to be supplied AC?

You're thinking 240vdc? (c;

Thanks.

Or whatever its nominal internal DC bus voltage is
 

[Seekonk]

I have a 100W 120V three phase VFD.  With no load I can easily drive 1 HP motors.  Not sure why you need something better.  But you can buy 3 phase boards with FET drivers pretty cheap <$20 and just add 6 FET and power supply.  Vary voltage with just a resistor.  Look up EG8010 boards (single phase) for a possible link to the 3 phase version

[iXod]

I have a 100W 120V three phase VFD.  With no load I can easily drive 1 HP motors.  Not sure why you need something better....

Usually not driving an AC induction motor, which VFD is great for. Sometimes need to power a PC board that uses 3-phase power (ie, machinery motor driver circuit) so other than 60 hz is a "no". So as much as I like VFDs and wish I could find a fixed-hz, variable-volts solution in a VFD I haven't seen this.

Thanks.

[Seekonk]

I still don't understand your need.  You say  "Need less than 10 amps." as if it is something trivial.

[Ian.M]

Definitely non-trivial. That's up to 6.25KVA @208V, 3 phase, and it would need a carefully tuned and balanced 20HP rotary phase converter, possibly with a resistive ballast load on the wild leg to reduce the swing between no and full load. Even on a NEMA 14-50 circuit, you'd probably need a soft-starter or a pony motor to spin it up to avoid it tripping the breaker.

[iXod]

I still don't understand your need.  You say  "Need less than 10 amps." as if it is something trivial.

Not trivial. Just quantitive.

[iXod]

Definitely non-trivial. That's up to 6.25KVA @208V, 3 phase,

Isn't it half that?

VA = sqrt(3) x 10 x 208 = 3602 ?

[Ian.M]

My mistake.  You'll be generating the missing phase for a 240V phase to phase wild leg delta supply, so that's  240V * 10A * SQRT(3) = 4157VA.   Rough rule of thumb for RPCs is you need twice as much idler as the max load, so you'd need a bit over 11HP.  Next standard NEMA motor size is 15HP.   If you actually need 208V delta (120V wye), you'll need  buck transformers

[Kilrah]

Can't you find 3-phase alternators with an exciter coil? Run it at fixed speed to get the freq right, then adjsut the voltage by changing the exciter coil current.

[Jeroen3]

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

[iXod]

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

Can you please describe design? Are these "built from scratch" or bought off the shelf? If so, what make & model?

Thanks.

[grifftech]

  just call your power company and ask them for 3 phase

[CatalinaWOW]

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

Can you please describe design? Are these "built from scratch" or bought off the shelf? If so, what make & model?

Thanks.

The second link I sent above is a rotary converter, available off the shelf.  Instead of a belt linking the motor and generator they are on the same shaft.  (Simple?)  They are available in various sizes, though the price increases rapidly.  Also a variety of vendors.  I don't have much contact with the technology, but no one I know who uses them has any fundamental complaints.  They take up room.  That's about it.