VFD driving a two-phase motor 1

[fab1961]

Dear all,

I need to run a small (less than 1 kW) two-phase motor (which in turn drives a cooling pump) for a shop test.
Motor and pump are designed for a 60 Hz supply, while in our factory we have 50 Hz.
My idea is to drive the motor with a VFD whose output frequency is programmed 60 Hz.
Point is that the motor is two-phase. I don't see problems connecting only two phases out of the VFD,
what do you think?

Thank you

Fabrizio

 

[LionelHutz]

Almost every VFD manufactured can only run 3-phase motors. You just might find some obscure device, but not likely.

 

[LittleInch]

Really?

https://www.amazon.com/Variable-Frequency-Drive-Single-Output/dp/B089PWJ3MG?th=1

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[LionelHutz]

LOL, Amazon is used as proof now. Let me know how that works out for ya.

The output circuitry in a VFD and the capacitors in a single phase motor don't play well with each other. There are/were a couple around for some single phase motors if you had access to both windings. Don't expect to just stick 2 wires from a 1-phase motor into a VFD and have it work. But then, don't just expect to connect the start and run windings of a 1-phase motor to a VFD and have that work either.

 

[jraef]

Assuming by “two-phase” you are referring to a single phase motor that uses 2-out-of-3 phases. Here in the US we have actual two-phase power still in use in a few areas, so that term can be confusing.

Single phase motors come in several “flavors”, meaning the design used to make them spin, because there is no relative rotation with only one phase. Of the 5 or 6 different types, only two are compatible with being used with VFDs, and one of those (Shaded Pole) don’t really need it. So that leaves ONLY the Permanent Split Capacitor (PSC) type single phase motors. They are used primarily on light duty applications like pumps and fans that don’t need a lot of starting torque, because they are weak in that regard. But still, pumps and fans are the biggest use of AC motors, so there ARE a few VFDs available for them. The only one I think is worth considering is Invertek, a UK based company. Because the sales volume is low, the price is higher than an equivalent 3 phase drive, so in some cases I have found it to be less expensive to use a 3 phase motor and a standard VFD that accepts single phase input, those are available everywhere and are very price competitive.

Most 3 phase VFDs monitor the output current to detect a loss of phase, so are not going to allow you to use only 2 phases on the output.

But if your application is a machine that is using a capacitor start or split phase type motor, you cannot use a VFD on them. So the 3 phase motor is the only real solution.

Ok, I just saw your drawing and it appears to be a pump, so it might be a PSC type motor.

" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

 

[LittleInch]

How does that TX work exactly?

Looks a bit odd to me so I'll let you sparkies argue it out....

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[waross]

This one LittleInch?

Top review from the United States
geoffrey cohen
1.0 out of 5 stars Would not start a single phase rotary compressor motor that runs normally on 6 amp 220vac
Reviewed in the United States on February 24, 2022
Size: 2 hp 1.5 kWVerified Purchase
I wanted this drive (which is rated on its nameplate as 10 amps) to soft start an HVAC PSC single phase compressor that runs normally on a measured 6 amps. Despite much changing of the set up parameters I could not get the drive to start the compressor. The drive remained stalled taking up to 13 amps before tripping the overload. Even using the extended data for these drives on the Gozuk website to change parameters did not work. There was also very good technical support from ATO who finally agreed that my compressor motor probably had a problem with the ATO output waveform. Amazon has agreed to a full refund.

Further, the diagram shows single phase motors.
Two phase motors started to be "phased" out in favour of three phase about 100 years ago. (There may be some pockets of legacy two phase power left. They would be using Scott transformation and three phase motors.)

But all is not lost.
You may be able to use a larger three phase motor on a VFD and then tap 60 Hz single phase from one phase of the motor.
You may have an issue with phase unbalance.
You may be able to trick the VFD by connecting resistor loads across the unused phases.
jraef will be able to supply better suggestions for coping with phase unbalance on the VFD.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[fab1961]

I have to apologize actually the motor is single phase...
I am an electronic engineer and sometimes don't use proper terms.
Once again this forum has been very useful to me and let me say thank you to everybody.

 

[jraef]

How does that TX work exactly?

Looks a bit odd to me so I'll let you sparkies argue it out....

You are right, it is odd, but I’ve seen things like it before, always from German machinery OEMs who seem to value technical capability over conventionality and the ability to attain replacement parts quickly (outside of Germany).

That is simply a single phase multi-tap transformer, with taps on both the primary and secondary to where you can input multiple line voltages and get not only multiple secondaries at the same time (in this case 24V and 230V), but they are also using one of the primary taps as an autotransformer to attain another 230V tap for this motor, likely to avoid needing to size the secondary kVA to be able to handle it. It’s clever to be sure, but if anything were to happen to that transformer, finding one set up like that will be nearly impossible, leaving you dependent on that OEM to sell you that part, assuming they are still in business.

The reason I know is that I have had to replace similar transformers for machines made by now defunct German OEMs, while the machine owners were breathing down my neck and upset due to their down-time costs. It was very frustrating.


" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden