My First VFD w 3-phase AC Gearmotor

[friquant]

Today I was able to bench test my first 3-phase AC gearmotor running on VFD. It's a foot-mounted Sew-Eurodrive 1-horsepower with 4.5:1 gear ratio.

Gearmotor

A four-pole AC motor typically has a speed around 1500 rpm when fed 60Hz power from the wall. With the 4.5:1 gear reduction, that puts us around 330rpm with wall power (60Hz). So long as the AC motor is 3-phase, we can add a VFD in the mix to control the frequency of the power going to the motor. And voilà, we have a motor that can go anywhere from 0rpm up to 330rpm. At least that's the theory I've been reading for the past few weeks...I hadn't seen any of this in action until today.

This ragamuffin came to me by way of ebay. Here is the original listing. I'll include a screenshot of the listing because these listings go away eventually.

This motor is bigger than I needed. 400 watts (1/2 horsepower) or maybe even 100 Watts (1/8 horsepower) would suffice. But this one I found for a song, only $65 after shipping.  I did verify that it was actually 3-Phase  before buying. (See the "3PH" in the upper right corner of the motor nameplate)

 

The box arrived a few days later. It was packed cozily in cardboard and foam. The outside of the motor is gritty. Perhaps it's been running in a moist environment.

The ad says it was taken from a running system. I'd like to clean it up and paint it, but I want to see it run first..

The wiring was set up for 380V, so I reconfigured according to the diagram for the 220V that my VFD will output. (My VFD takes 110V single phase as input, and outputs 3-phase in the range of 220V.) Here is before and after, note the copper strips have been repositioned under the nuts to effect the wiring change.

 

VFD

The VFD (variable frequency drive) I've actually had for a couple weeks while I've been looking for motors. But I've never owned any 3-phase equipment so had no way to really test the VFD, hence the excitement when the gritty box finally arrived. 🤪  Here is a link to the VFD I'm using: https://www.amazon.com/dp/B0D53Z7RZ5

And a screenshot:

Here's what the back of the VFD looks like.

The two red "AC" labels are for neutral and 110V single phase input. FG is ground, connecting both to ground in the wall outlet and to the ground on the motor. The blue U, V, W are the 3-phase outputs which the VFD can control to be any frequency from 0Hz up to I think 100Hz, which is how the VFD accomplishes speed control on an AC motor which would otherwise be fixed speed.   

The green strip on the right is for low voltage input/output. One of them can be used with an external potentiometer to set the frequency. I've ordered a TIG pedal for this but it has not arrived yet---So today we'll use the built-in potentiometer/knob on the front of the VFD to control our speed.

Bench Test

Here we are on the bench:

And a video

Many thanks to @GerryR who has fielded a LOT of questions from me as I've been pursuing this journey.

[friquant]

Got it cleaned and painted

Here it is set up temporarily with the Singer 31-15

 

And a video of how it operates using the TIG pedal's contact switch and potentiometer to activate the VFD when you step on it.

 

Would like to find a reliable, inexpensive source for these gearmotors so we can set up a recipe or parts list for anyone who wants to go this route.

 

[Cumberland Highpower]

That's pretty awesome.   

Im left wondering a bit.  With a VFD you probably shouldn't operate your motor under 400rpm (it might overheat).  With the 4:1 reduction that would put you down to 100rpm.  Of course the reducer might allow you to cheat the overheating part by allowing less load at low rpms so maybe you could push it lower under load?

Have you had any trouble with overheating?

Edited August 4 by Cumberland Highpower

[friquant]

54 minutes ago, Cumberland Highpower said:

That's pretty awesome.   

Thanks! I've been enjoying it 🤠

 

54 minutes ago, Cumberland Highpower said:

Have you had any trouble with overheating?

None so far. My duty cycle is quite low in general as I'm typically spending much more time thinking about sewing and planning the design than I am actually stitching. The only instances where I can see a good use for going ultra slow is at the start of a seam (when I'm scrambling to make sure I've got the thread held down while also driving one-handed), and at a corner or end of a seam when I might slow down to make sure I bury the needle when I let off the gas. The middle sections, especially of straight seams, warrant higher speed else one gets bored.

I conjecture that a few seconds of ultra-low speed at the beginning and end of each seam, even if they do cause extra heat (I'm unclear on this point) won't cause enough extra heat in those few seconds to cause any trouble---the  heat will be absorbed by the mass. As far as what could potentially overheat, and how to measure & test that, I'm open to suggestions. 

VFD
This VFD has a temperature sensor for itself, and you can specify what temperature is too hot and it will disable at that temperature.

Motor
This motor does not have a temperature sensor that I know of. I could imagine nesting a thermistor between the coils of the stator and running the thermistor wires out through the electrical box along with the power wires. 

54 minutes ago, Cumberland Highpower said:

maybe you could push it lower under load?

I have not adjusted the volts-per-hertz settings at all yet, but that's worthy of testing out. I wish this VFD had a setting for overall reducing the amount of current (torque) going to the motor, but I haven't found a setting for that yet.

[dikman]

Impressive, lots of torque there. I doubt if overheating is likely to be a problem for home/hobby use. It sounded pretty noisy, or is that just an overly sensitive mic?

[friquant]

42 minutes ago, dikman said:

It sounded pretty noisy, or is that just an overly sensitive mic?

The motor howls---I suspect it's a bearing inside the gearbox that has a pitted race. I have not been able to get the front cover off the gearbox. Next time I'll tap it with a sledgehammer to knock it loose.

The VFD has a noisy fan too, but the motor howl is the bigger problem. 

[friquant]

Here's how to replace the bearing on the gearbox end of the motor shaft.

There is a big circlip on the motor side of the gearbox. (There will be a photo later) Make sure you remove that before you do any pounding

This first image shows the gearbox after you remove the four cap bolts and pull the cap off. This model has two dimples in the shaft to mushroom it out to keep it on. I moved the dimples back inline with the shaft using punch, then used a 1/4 inch drive socket extension and a sledgehammer to drive the shaft out.

 

 

 

Here is the bearing that needed replacement the most. Note the large circlip behind it---that's the one you have to remove before you do any pounding.

Now that the bearing is out of the gearbox, I used a 3-jaw puller.

By the way, notice the paint on this one is white. This is a second gearmotor (same make and model) from the same ebay seller. This time better paint, but still needed a new bearing. I replaced both bearings on the  motor shaft, both are size 6203. I did not replace any bearings at the gearbox output shaft. They turn smoothly already, and they get a lot less revolutions than the motor bearings!

Good news is, this motor runs semi-quietly with the new bearings. (Makes an oompah sound like you might imagine used as a movie sound effect in an eerie movie) I'll be replacing the motor shaft bearings on the other motor soon.

Edited 8 hours ago by friquant

[friquant]

I opened up the VFD and disconnected the fan. The VFD has thermal protection, currently set to trigger at 90 degrees C, so I'm not worried about overheating it with the low duty cycle I'll be putting it through.

Here's a video to show the sound level without the fan

 

 

[TomE]

Smooth operator.  Looks like a success story.

[dikman]

Always hard to tell from a mic input as sometimes they can be overly sensitive but definitely better than before!