Strange VFD issue?

[daved20319b]

I have an 80's vintage belt drive Grizzly 12x24 that I recently did a 3 phase conversion on. I was having some issues with torque loss, the machine was way too easy to stall, a .020" DOC in mild steel would slow it to a crawl, any more than that would bring it to a complete stop. I did some digging and finally decided to pretty much start over with the VFD programming. VFD is a 2 HP Teco-Westinghouse L510, single phase 240 volts in, 3 phase 240 volts out, feeding a Leeson 1.5 HP 3 phase IEC motor. I was initially running it in sensorless vector (SLV) mode, but decided to start over in voltage/frequency (V/F) mode, mostly to see if it made any significant difference. I ended up doing a factory reset on the VFD, just switching back to V/F mode left behind some settings that I couldn't seem to unset.

So I got it reconfigured and all seemed fine, although my surface finish kind of sucked. I was running in lowest regular (not back gear) range, supposed to be 320 RPM at base frequency. Decided my tooling was part of the finish issue, so upped the speed to the next range (490 RPM), and switched to a carbide tool. This allowed me to get the DOC I was after, ~.050", but finish was still pretty lousy, even with a very slow feed and light DOC, so I decided to speed it up again. And this is where it got weird. I'd been monitoring output current as I went, the VFD is rated for up to 7.5 amps output, and up to this point, it hadn't gone up to 3 amps. But as soon as I shifted into the next speed range (690 RPM), the current spiked to over 9 amps running no load other than the chuck and drive train . And to make a long story short, switching to the high range motor pulley was no better, even though the speed was lower. Increasing the frequency to the motor helped, I have it limited to 90 Hz. and once I got over about 75 Hz., the current went back below 7.5 amps.

So I guess I have a couple of questions. First, is this normal, so nothing to worry about? And second, what do I need to change to fix it if it's not? I had no current issues running in SLV mode, but I also had no cutting torque. And surface finish sucks no matter how it's running, although that could be totally unrelated, and just a factor of the material I'm cutting (4130). I did use it before on both aluminum and an iron pipe fitting I needed to modify, finish on both of those was pretty good, but not great. Any suggestions or insights would be much appreciated, thanks.

Dave

 

[mksj]

What is the model number of the Teco L510, is the motor correctly wired for 230VAC. VFD’s when tamping up to speed can spike higher current, but once at speed uloaded I would expect a current of around 40-45% of FLA. Assume current is the VFD display not a current clamping.

Should have no difficulties with DOC with that combination and size lathe. Recheck the motor parameters, in SLV you need to run autotune.

 

[IHinIN]

Definitely check the motor to make sure it’s set up for 230V. I was pulling out my hair trying to figure out the VFD settings on my mill because the motor was weak and easy to stall. It ended up that the motor was set for 440V not 220V like the label on the motor says. The previous owner obviously was running 440V in his shop and changed the motor. I switched the motor over to 220V and it runs great now.

 

[daved20319b]

What is the model number of the Teco L510, is the motor correctly wired for 230VAC. VFD’s when tamping up to speed can spike higher current, but once at speed uloaded I would expect a current of around 40-45% of FLA. Assume current is the VFD display not a current clamping.

Should have no difficulties with DOC with that combination and size lathe. Recheck the motor parameters, in SLV you need to run autotune.

Full model number on the VFD is L 510-202-H1-U. I went to some pains when first wiring the motor to make SURE it was set at 230 volts, but it's always possible I got a lead wrong, so I'll be double checking that. My issue is that it seems to be related to spindle RPM, at 320 or 490 RPM, it was barely showing over 2 amps. The third step in low range is 690, soon as I tried to start it up there it went to about 9 amps output and stayed there. Since the lowest speed in high range is 600 RPM, I decided to try that, same result, although like I said before, if I turn it up over 75 Hz., it comes back down sort of where it should be. By the time my testing got to this point, the lathe was fully warmed up but not hot. Another tidbit, if I pull the motor belt off, it runs fine and draws almost no current throughout the range (30-90 Hz.). I could understand a spike at startup, then falling back, but this goes to more than 3X the output of the previous 2 speeds and stays there. And 9 amps is also twice what the motor is rated for. I'm also a little confused that the VFD will even put out that much current, I thought it maxed at 7.5 amps. Color me still confused.

Dave

 

[den-den]

How are you measuring the current? "almost no current" does not make sense to me and makes me question all the amp readings.
Most VFDs are capable of putting out more amps than they are rated for but only for a short time.

 

[daved20319b]

How are you measuring the current? "almost no current" does not make sense to me and makes me question all the amp readings.
Most VFDs are capable of putting out more amps than they are rated for but only for a short time.

My apologies, that was poor wording on my part. As to how I'm measuring the current, I'm not, I'm going by the VFD display, I have it set to toggle through a variety of display parameters. So running just the motor, output is ~4.5A from 30-45 Hz., over 45 Hz. it drops to 1.8 or so, then gradually tapers down to ~1.2A by the time I hit 90 Hz. It doesn't like running under 45 Hz. in V/F mode, one of the reasons I was initially using SLV mode. And in response to an earlier comment, I ran auto tune in both modes.

Running under load in the two lowest speed ranges at about 60 Hz. output was ~2.4A, with a fairly health DOC that went to about 2.8. But as soon as I select a belt setting over 500 RPM, it jumps to 9A output just turning the chuck. I don't know how long it would run that way, I didn't let it go more than about 30 seconds, I didn't want to risk damage to either the motor or the VFD. Still looking for answers, thanks for your input, later.

Dave

 

[daved20319b]

Okay, I'm feeling a little stupid right now. The motor is new but discontinued, dual voltage, and arrived wired for 460 volts. I THOUGHT I was being oh so careful when I rewired it for 230 volts, but I actually had it all buggered up, neither 460 OR 230 volts. Got it rewired, correctly this time, and it runs great, huh, go figure . Anyway, I think I finally have the electrical end of this beast sorted, thanks for all the help and suggestions. Later guys.

Dave

 

[IHinIN]

Good to hear that you got it fixed.
I felt stupid myself for assuming my motor was wired for low voltage and not checking it until last week.