cosφ

An Alvitar ATV312 VFD I acquired requires a cosφ entry in the motor specs setup. My motor does not give a value for that. So not having any idea what it is, I Google for a way to calculate it. I never found anything I understood, but I did find some ranges for different 230V 3 phase motors, which I have. For 2HP it was .81 or .84.

So I enter all the values and the drive functions as normal, but the motor is making some strange rumbling noises, as well as what sounds like bad bearings. Odd because the motor has 5-10 hours use since I acquired it new.

I haven't used the lathe a in long time, and I'm really confused by this, so I tear the motor apart. I found nothing wrong with it. I hook the WEG VFD that was on it back up and the motor sounded fine.

I hook the Alvitar back up and start changing motor value settings at random. No improvement. The last setting is cosφ. The value range is .50 to 1.00. First value I try 1.00. The motor ran perfect. Problem solved.

My question: Is there an explanation for what cosφ is that someone with little knowledge about electronics can understand? And why was the wrong setting causing the motor noises?

That’s the European way of saying “Power Factor”. Most motors here don’t show that, just use .8. It’s not that important to the drive.

It is indeed power factor. The drive may be using it as a measure of something else the programmers were interested in. When you entered 1.00, you basically told the drive to forget about the measurement, so it did, and works fine, like other drives that do not mess with it.

The 1.0 value told the drive that there was no point looking for magnetizing current, because a 1.0 PF has no inductance involved, it is purely resistive. What it actually did with that number I cannot tell you for sure, but it likely zeroed out a value for some parameter.

Motors vary a lot in PF at full power, probably anything from 0.6 to 0.85 is reasonable for that size, depending on design. The power factor at no load is usually horrible, often around 0.1 or 0.15 for a standard induction motor.

If the drive was in vector mode, it should not have even needed that number, as it would measure the parameters it wanted.

Did you run a full motor analysis/tune? That will generally overwrite the values that might not be on the nameplate, and is critical if you're running in vector mode, and still advisable in V/Hz.

Thanks everyone.

It was originally set at .81 or .84, I don't recall exactly. And at that setting the motor was definitely making some weird noises. Enough to prompt me to tear the motor apart looking for the cause of it. And changing it to 1.00 completely eliminated it. So for whatever reason that setting definitely makes a difference. Puzzling that .81-.84 was a problem. The info I found and what JST says implies that it should have been fine.

I think I ran autotune but I don't recall. I definitely didn't get to torque settings. I started tearing the motor apart before I got to that.