Motor & VFD Sizing for Lab Stirrer/Mixer

[Xsailor]

Hi,

In my plant, we use a few Lab mixers for stirring-up chemicals and mixing them. Some of the mixtures, nearing their mixing times, can get rather thick and viscous.
In the past, a few Universal AC/DC motors (with Gear boxes and Speed Controllers) have served us well barring frequent carbon brush changes and repairs to the rheostats.

I was planning to install a 3ph AC Motor and VFD to replace one of the mixers.

Current Motor specs are;
With no gear box, motor is 2.5Amps 1 phase 220/230 50 Hz, 1/2 hp, 0.37 KW, 6000 rpm and 3.00 Kg-CM torque
A 42:1 gearbox is used which brings max speed to 140 rpm and max torque to 12.35N.

Limitations/Requirements:

- Single phase AC 230V. Lack of 3 phase supply in the mixing area. This was one of the reasons my predecessor bought the Universal AC/DC motors.
Understand that some VFDs accept single phase inputs and can still drive 3 phase motors.
- RPM control must be by a rotary knob/pot know as frequent changes are required – push button may not be durable in the long term.

I was considering the 186rpm/16Nm/0.37Kw (Box040) here http://www.rotomotive.com/tabelle_prestazionali_02.pdf

Now comes the difficult part – I have never bought a VFD – ever and haven’t the faintest idea on spec-ing those!
After reading on the web, I was able to gather that a sensor less Vector drive will maintain torque along the spectrum of speed and not cause severe torque issues at low rpm (we tend to run the drives along all rpm bands depending on thickness and quantity of the fluid).

Any help in this area will be appreciated.
I will be sourcing locally from India but I may be guided using AutomationDirect as a benchmark.

Thanks in advance.

Amit SETH
Xsailor

 

[Norml]

I believe that most if not all VFDs can accept single phase input. A rule of thumb is to double the horsepower rating of the VFD. (The multiplier is actually the square root of 3). I've used a lot of Toshiba drives and the smaller ones have a built-in pot for speed control. External pots can also be used by changing a parameter in the drive.

 

[DickDV]

Without getting into a lot of detail for your specific application, I would think that a TENV motor rated 230V 3ph .37kw or .5hp would be the choice. With TENV you have an enclosed motor and no cooling concerns over the whole speed range down to zero speed.

The drive should have a short-term or one minute output amp rating of at least double the motor's FLA. That probably will mean a 3/4hp drive. At that rating, you can buy drives that are designed for 240V single phase in and 230V three phase out. No derating needed. Also, be sure to buy a drive with sensorless vector capability to ensure good motor performance a very low speeds.

There are many good drives out there for this application. One of them would be an ABB model ACS355. I am very familiar with them and am sure it would meet your needs.

As to a speed pot, I would recommend an industrial grade oil-tight speed pot mounted separate from the drive. While some drives come with front panel speed pots, continuous lab use will destroy them too quickly. Better to get an industrial grade pot that will last a while and also be sealed up against contamination.

 

[Xsailor]

Exactly the reason I visit the forum EVERYDAY - Great Help is always available.
Thank you so much DickDV and Norml.
DickDV: I have read and reread so many of your threads in the past year. When I posted, I was secretly wishing that you answer.
Someday, I am going to make a winder/unwinder machine just to learn to tinker with all the nuances of a VFD.
Gosh! How I wish I had studied to be an engineer.
Thanks so much for posting a suitable reply - I really do appreciate it.