Motors not working with VFD. No full speed

Hey All,

I'm trying build myself a 2"x72" belt grinder. I managed to get a handful of 1.5HP 3-phase motors to use with a VFD for the grinder, but for some reason they're not playing nice with the VFD. I have multiple identical motors (Leeson) that came out of commercial treadmills. I was told that they work (for what that's worth).

The motors are 230V only (no high voltage) and have five lines coming out. P1 and P2 are marked to go to a thermostat (they're NC based on the multimeter). I left them disconnected for checking to verify the motors work. T1, T2, and T3 go to the three 3-phase lines based on the wiring label.

When connected through the VFD and powered on (should ramp up to 60Hz over 30 seconds), they ramp up to about 4.5Hz unsteadily and stop there. The rotation didn't seem smooth to me. I didn't leave the VFD on for an extended period for fear of hurting something. I tested multiple of these recently-acquired motors with the same result.

For now, the VFD that I'm using (2HP rated, TECO JNEV) is used to power a 2HP motor on my bandsaw with very similar specs. I reconnected the VFD to the bandsaw after this testing and verified that it still ramps that motor up to full speed smoothly.

I put a multimeter across the T1, T2, and T3 lines on the motor. All were open to ground, and there was about 2.0 ohms between any pair of the lines. So my impression is that the motors aren't bad.

Any thoughts on what the problem might be and what I can check?

Thanks,
Tyler

OneStaple said:

Hey All,

I'm trying build myself a 2"x72" belt grinder. I managed to get a handful of 1.5HP 3-phase motors to use with a VFD for the grinder, but for some reason they're not playing nice with the VFD. I have multiple identical motors (Leeson) that came out of commercial treadmills. I was told that they work (for what that's worth).

The motors are 230V only (no high voltage) and have five lines coming out. P1 and P2 are marked to go to a thermostat (they're NC based on the multimeter). I left them disconnected for checking to verify the motors work. T1, T2, and T3 go to the three 3-phase lines based on the wiring label.

When connected through the VFD and powered on (should ramp up to 60Hz over 30 seconds), they ramp up to about 4.5Hz unsteadily and stop there. The rotation didn't seem smooth to me. I didn't leave the VFD on for an extended period for fear of hurting something. I tested multiple of these recently-acquired motors with the same result.

For now, the VFD that I'm using (2HP rated, TECO JNEV) is used to power a 2HP motor on my bandsaw with very similar specs. I reconnected the VFD to the bandsaw after this testing and verified that it still ramps that motor up to full speed smoothly.

I put a multimeter across the T1, T2, and T3 lines on the motor. All were open to ground, and there was about 2.0 ohms between any pair of the lines. So my impression is that the motors aren't bad.

Any thoughts on what the problem might be and what I can check?

Thanks,
Tyler

View attachment 211442

Click to expand...

Resistance showing on an ohmeter doesn't necessarily mean the windings aren't going to allow current to flow when the potential is 230V. When testing with an ohmeter, you are putting 9VDC on the windings. If the insulation is failing, it may still provide a proper resistance against such a low voltage. You really need a megohmeter (megger) that energizes the windings at a high voltage (500V in this case) and looks at the voltage drop across them. Since it's unlikely that you have one, take it to a motor shop and ask them to test it for you.

Chances are that these motors failed a long time ago, that's why you got them so easily. The VFD is protecting itself by limiting the current, and to do so, it ceases the ramping of voltage and frequency.

It seems odd that all have the same form of failure that is just bad enough to not work with the VFD but not a hard short that a DMM will show up. Possible, but unlikely unless the type has a known issue, But the fact that they are "takeouts" is somewhat supportive of the idea.

And, to "work unsteadily", the VFD would have to be set to limit current but keep trying, as opposed to a "trip-off" condition. Did you set that up for the bandsaw?

What I am seeing is the 2 ohms, That seems a bit low for a motor of that size, although not out of the range of credibility. They could be mismarked, and then might be some other actual rating. That is slightly more possible due to them being for treadmills .

A design B motor is not the lowest start current type, so the motor may draw a fair bit of current as it is accelerated.

What have you set the VFD up with?

Did you change the setup for the new motor, or did you just use what you had in place for the bandsaw?

Specifically, what did you have for "motor rated current"?

Is there any low end boost setting that is turned on? (May be called an HVAC setting)

Have you tried setting the accel to a much FASTER speed? Sometimes the VFD will not start a motor slowly but WILL start if faster, because there is a time delay on the current trip point. Going slow may "time out", where a faster accel is over before the timeout expires.

I would try setting accel to 3 seconds as a check.

JST said:

It seems odd that all have the same form of failure that is just bad enough to not work with the VFD but not a hard short that a DMM will show up. Possible, but unlikely unless the type has a known issue, But the fact that they are "takeouts" is somewhat supportive of the idea.

And, to "work unsteadily", the VFD would have to be set to limit current but keep trying, as opposed to a "trip-off" condition. Did you set that up for the bandsaw?
...
Is there any low end boost setting that is turned on? (May be called an HVAC setting)

Have you tried setting the accel to a much FASTER speed? Sometimes the VFD will not start a motor slowly but WILL start if faster, because there is a time delay on the current trip point. Going slow may "time out", where a faster accel is over before the timeout expires.

I would try setting accel to 3 seconds as a check.

Click to expand...

He has the little TECO NEV drives. They don't have an "Autotune" function for their so-called SVC mode (because it isn't really SVC, but that's a different issue). So there are no settings other than motor FLA that he could change, and if the drive were left programmed for a 2HP motor, it should not have had any trouble accelerating a 1-1/2HP motor.

There is also no specific "current limit" function, but it does have "Stall Protection on Acceleration", parameter C01 and 02. If C01 is 0001, then Stall Protection is turned on, and the drive will automatically reduce the voltage and frequency (and carrier frequency) until the motor either accelerates or the drive eventually trips off on Over Current.

Faster accel time would have no effect or even exacerbate the problems if I'm correct.

Everyone who sells a used motor claims it was working when they removed it. Otherwise they would not try to sell it, they would just scrap it, or at least the honest ones would...

If P1 and P2 are supposed to go to a thermostat, does that mean that the motor is effectively shut off unless the thermostat closes the connection between them? Or is there some other functionality intended there?

Success! Reducing the acceleration time back to the default of 5 seconds got the motors spinning just like they should. No issues now. I had a slow acceleration because the mass of my 32" bandsaw was kicking the overload if it accelerated too quickly. Didn't think it would be a problem for an unloaded motor, other than the wait time.

Jraef - I agree about ideally using a megger to verify no breakdown in insulation, but I didn't have one accessible. And you're right about the description of my TECO JNEV being a fairly simple VFD with little I can change.

JST - These motors that I'm testing are almost identical to the motor on my bandsaw, so I didn't bother changing any settings when testing the "new" motors. Looks like I should have adjusted acceleration, as you suggested. Once I set these motors up for a belt grinder, I'll certainly customize the settings on a new VFD to match the motor setup.

JLarsson - My understanding is that P1 and P2 connect to an internal thermostat (probably bimetalic strips). The two probes should be connected in line with the low-voltage power controls (on/off switch). The path between P1 and P2 is normally closed/shorted, but in the event of overheating, they will open. If connected to the power controls, they should turn off the motor. In my situation, when I'm just making sure these motors turn on, they can be ignored. When the motors are put into service, it's a good idea to integrate P1 and P2 into the motor controls properly so as to adequately protect the motor. All of the above description is simply my understanding from some google research, and I certainly don't pretend to be an expert on this at all, so take it with a grain of salt.

Thanks to all for the help!

Tyler

Glad you got it working. And I learned something, as usual around here. Thanks.

Super!

That accel thing is totally counterintuitive, but often works, due to peculiarities of the VFD overload capability, and/or load characeristics.

And it is not just low inertia loads that can and should accel faster. We had a large heavy direct connected blower wheel on a 3 HP motor, With a slow accel, it tripped. With a fast accel it tripped. But between the two was a whole big range of accel times that were fine. we ended up setting in the middle of that range and there was never an issue in production of the unit.

Yeah, I'm glad you suggested changing the acceleration. It never would have occurred to me as a potential problem.

Since my band saw (32" cast iron from 1905) has so much inertia to overcome, I have the slow acceleration set and also help on startup by starting the wheel spinning by hand.

Thanks again!

Tyler