I got my hands on a cheap Variable Frequency Drive that I was hoping to experiment with. It's a Yaskawa GPD205 (here's a link to the manual: https://www.yaskawa.com/delegate/ge...2&cmd=documents&documentName=TM4502GPD205.pdf) and it puts out three phases over three wires. Since there's no forth neutral wire I'm assuming it's delta 3 phase power and not wye but the manual doesn't state either way. Could I connect a single phase 120V motor by connecting it to two of the three wires? I know with a wye connected source you can connect a single phase motor between one of the phases and neutral but I'm not sure how to do the same with a delta source where the is no neutral.

Assuming there is a way to make the connection what would happen if it is indeed a wye source that's missing the neutral and not a delta source?

Thanks,
Harry

 

The VFD wont run a single phase motor.

It will see the unused phase and know something is wrong and not work.

 

The VFD wont run a single phase motor.

It will see the unused phase and know something is wrong and not work.

Would it be possible to run two or three single phase motors so that all the phases are used?

Thanks,
Harry

 

Not really. the way a VFD generates its output (phase interleaved PWM) it highly dependant on it being sent to a three phase motor with interconnected wiring and magnetic fields on one motor core.

That, and common single phase induction motors large enough to work with a VFD are not speed controllable to any significant degree anyway.

Shaded pole and split capacitor run types that re typically in the fractional horsepower are about all that can handle variable speed operation and they can typically be speed controlled with phase angle voltage control similar to how a common incandescent light dimmer works with.

 

I don't have details of the model, but I used one in grad school to run a 3hp single phase motor for months without issue. Just hooked up two phases. Now that i know more, I wonder why it worked.

So one anecdote where it worked.

 

I don't have details of the model, but I used one in grad school to run a 3hp single phase motor for months without issue. Just hooked up two phases. Now that i know more, I wonder why it worked.

So one anecdote where it worked.

Could be a single phase VFD.

 

Could be a single phase VFD.

Nah, good thought though. We moved the lab and I replaced motor with 3 phase one at some point. I may try to email someone and get the specs. Very curious now.

 

Apart from stated above, the reason you do not see many 1ph VFD's for 1ph induction motors is they tend to drop out of run when ran under load especially at low RPM.

but I used one in grad school to run a 3hp single phase motor for months without issue

I assume by that you mean you ran a 3ph motor on 1PH?
If so if you get it to rotate first by external means, in some cases a 3ph motor will run off load.
If you mean you ran a 1ph motor off of 2phases of course it will, 2 phase IS 1ph.
Max.

 

OK..Here is the real question.
Wouldn't a missing phase current trigger a fault.
May be the VFD can be configured as a single phase one.

 

I have never personally come across a 3ph VFD that will satisfactorily run a 1ph motor without a problem, and I have used quite a few makes over the years.
Also I did try to run a 3 winding BLDC motor off a VFD but with poor results.
Although I believe there are 1ph VFD's out there in a limited sense, The cost of 220v 3ph motors on the surplus market doesn't usually warrant the risk. Particularly with the choice of using a VFD on 1ph 240v supply.
Max.

 

I agree.
It's a poor choice to run a 1ph motor of a 3ph VFD.
The 3ph motors are smaller than the 1ph motor of the same HP

 

I agree.
It's a poor choice to run a 1ph motor of a 3ph VFD.
The 3ph motors are smaller than the 1ph motor of the same HP

That is for sure. Once I got a 'correct' system up and running, life was much better. I was running a liquid pump and needed to control flow. Was using a diverter valve set at full speed. VFD on 3ph so much more controllable. And quiet.

 

The 3ph motors are smaller than the 1ph motor of the same HP

I have many that show otherwise. Same HP in the same frame from the same manufacturer regardelss of whether they are single or three phase.

 

I don't have details of the model, but I used one in grad school to run a 3hp single phase motor for months without issue. Just hooked up two phases. Now that i know more, I wonder why it worked.

So one anecdote where it worked.

Not impossible if it was an old and very basic unit by today's standards that had no real phase to phase current monitoring and the motor was small plus not being ran too far off from its primary frequency and speed or if it was a split capacitor or shaded pole unit.

No modern VFD will allow any motor to run in a single phase condition by design.