VFD for non-capacitor single phase motors

[nanok]

Hi all,

I am in the brewing industry and I accidentally purchased a Goulds pump that was meant for 50Hz service (typical for Europe but not USA). I unfortunately cannot return it so I was looking to find out if I can use a VFD to control it's speed or at least bring my 60Hz service down to 50Hz.

I have plenty of experience with VFD's I have several currently in use within the brewery. But they are all used with 3-phase power and 3-phase motors.

I have read that there are special cases where you can use a VFD to control the speed of a single phase motor. This link explains the type of motors that can be controlled with a VFD even if they are single phase:

https://www.wolfautomation.com/blog/vfds-for-single-phase-motors/

To paraphrase, it says these following motor types could be controlled with a single phase VFD:

Permanent Split Capacitor (PSC)
Shaded Pole Induction Motor
AC Synchronous

The motor I purchased is this one:

https://www.pumpcatalog.com/goulds/npe-npe-f-316l-ss-stainless-steel-pump-series/1st4d4d4/

I was wondering if anyone could tell me which above category (or other category) this motor would fit into?? Beware the photo on the website is not the actual product photo. This motor does NOT have a capacitor. I attached my photo of the actual product, you can see there is no capacitor. I appreciate any info y'all might have!

https://files.engineering.com/getfi...40-9742-8a80b33c3544&file=20210125_151530.jpg

 

[dArsonval]

The capacitor for your motor is likely secured under the shroud end or back end. Removing the cover will reveal the capacitor.
It also looks like the motor is rated for either 50, or 60 Hz operation. (Based on the attached photo.)

John

 

[waross]

Suggestions:
Forget the VFD.
Run the motor on 60 Hz.
To maintain the V/Hz ratio, use an auto-transformer to boost the voltage up to 265 Volts.
1.> Redneck solution. Throttle the discharge to bring the current down to or below the nameplate current rating.
2.> Trim the diameter of the impeller so that it is suitable for use at 3500 RPM.
3.> Contact Gould and request a replacement impeller that is suitable for 3/4 HP at 3500 RPM.


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

 

[waross]

Good catch dArsonval
No need for a transformer.
Try it and watch the current.
Look at impeller solutions if the motor overloads with the present impeller.

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

 

[jraef]

What is the actual problem you are trying to solve here? The motor is rated for 50or 60Hz, it of course spins 20% faster at 60Hz, so the pump will move more fluid and require more HP to do so. But that then depends on how you sized it in the first place. As Bill has said, you can probably just restrict the flow and get the same net effect as reducing the speed to 50Hz.


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

 

[TugboatEng]

Keep in mind, 3/4 horsepower motors here in the USA are ~$350 so you don't have much room to work with before you exceed the cost of simply buying the right motor.

 

[zlatkodo]

HI, Nanok,
I would redesign (rewind) from a single-phase to a three-phase motor.
Then you can use standard VFD.
Regards
ACW
Winding Design and Motor Repair

 

[itsmoked]

If you buy the same frame motor in 3-phase and hook it up to a cheap VFD it will absolutely work.

Buy a single phase VFD for a fortune and it might work..

I'd just replace the wrong motor and sell it.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[waross]

1/2" Gate Valve Stainless Steel SUS SS 316 CF8M Heavy Duty NPT
3.8 out of 5 stars 3
$14.44
Amazon.com

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

 

[TugboatEng]

Change that to "globe valve* and that is certainly an option.

 

[waross]

I agree Tug, with two caveats.
After searching returned pages, I got lazy and took the first suitable valve that I saw.
A globe valve may be a better choice but over the years I have successfully throttled up a number pumps when all that was available was a gate valve and it was not within my scope to change the valve.

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

 

[Marke]

https://www.invertekdrives.com/variable-frequency-drives/optidrive-e3-single-phase

Mark Empson
Advanced Motor Control Ltd

 

[crshears]

Larger concerns are no less immune to throttling with gate valves, sub-optimal though it is . . .

I once recall upon a dewatering pump being placed in service that it had to be throttled with an 18" gate valve so it wouldn't trip on overload; nobody higher up could be bothered with having the design flaw corrected, so it was up to us poor operators to use valve wheel wrenches to, as required, adjust the valve against the significant lateral binding pressure, put up with the nasty noise, racket and vibration [ by donning hearing protection ], and so on. Thankfully [and eventually] once some head had been developed by the advance of the pump-down operation the gate valve could be opened wide.

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

 

[nanok]

Thanks everyone for the input. Yeah it says running at 60Hz will reduce the life of the motor. It's only going to be used for an hour or each week so I suppose a valve on the output would work fine to throttle the output down.

It is for wort (beer before it has alcohol) so I don't really like the idea of always running it full speed because excess oxidation of wort is possible with the thrashing of the impeller, but as you guys pointed out, it would probably be a MUCH more expensive solution to actually get this thing running with true VFD control.

Appreciate the suggestions!

 

[TugboatEng]

"Thrashing of the liquid" sounds like shear. If shear of the fluid is a concern you should be looking into pumps that don't have any radial component to their flow such as diaphragm pumps.

 

[nanok]

Not exactly worried about shearing of the liquid per se, just worried about air bubbles that might get temporarily trapped in the head of the pump and if the pump is going full speed it's mixing the air and my wort excessively.

I think you guys collectively nailed it tho. It's not super critical to prevent this excessive mixing and sounds like it's a can of worms to actually get a single phase VFD working for this pump. Not to mention whoever pointed out that a capacitor MIGHT be hiding under the end cap of the motor, that would certainly make the VFD a no go.

 

[TugboatEng]

Just as one final note, the air doesn't enter the fluid in the pump. Thoughtful design of you pump inlet and piping as well as the use of air separators to minimize entrapped air should be considered.