Motor sounds like it's crushing a load of gravel...

At the risk of sounding like an idiot (because I haven't done a more thorough investigation yet) - I'm going to throw this question out there...
I hooked up a new machine (5Hp Lathe) to my rotary phase converter (10Hp) and it sounds like it's crushing up a load of gravel. It starts and runs just fine, but is noisy. When the switch is turned off it gets quiet, even when the spindle is still spinning down (so I'm assuming it's not mechanical). It's a little quieter at higher spindle speeds (higher motor loading?). There is also a 2Hp mill and a 1Hp grinder hooked up to the converter that work/sound fine.
Anyone have any ideas/suggestions?

Thanks,
Joe

Usually converter problems such as blown capacitor, stuck start capacitor during run, etc., cause a very loud serious-sounding vibration sound, much like those loud fire alarm buzzers used in buildings.

I've never heard a sound like you describe except when it was coming from a gearbox, where the cause was obviously mechnical.

bnelson

You are using 180 apart power pulses to power a 120 degree device. Using capacitors and resistors inside (the convertor) to modify the residual voltage to simulate a third wave. (note that two lines directly connect to the motor leads, still at 180 degrees) Yeah.. it is running out of phase, putting a larger motor running (idle) will help dampen the harmonics more and make it less noisy. Tesla designed the 3 phase power to be near perfect and economical, hard to make it work from single phase correctly.
MY bridgeport mill sounded like crap with one of these. I put a 200 dollar single phase in 3 phase out inverter and it runs great. I got the model number if ya want it. Maybe a twist lock plug would make it valuable to several motors by putting male plugs on the other devices.

Joe,

Can you start up your lathe and give us the three voltages and currents during noisy operation. If you can, do it under load when it’s most noisy. If you cannot measure both current and voltage at the lathe motor leads, just give us one or the other.

If ibewgypsie is right about significant phase imbalance, it should show up in the three voltages and/or currents. Your 10 hp converter, if working correctly, should be big enough to give 120 degree separation; if not, maybe your converter has an open run capacitor, in which case the phase to phase voltage on one side of the generated leg should be very low (say below 220 volts) under running load.

A run cap is easy to replace and not too expensive.

bnelson

Joe,
I think bnelson and ibewjypsie are on the right track. If you did have an open run cap it could make those types of noises. I never did hear one like that but it is always possible. Electricity can do very strange things sometimes. Please let us know what you find. Good luck.

ibewgypsie, I'd like to know what your using, if all else fails I could put an inverter on the problem machine and still run the rest off the phase converter.

bnelson, It's actually noisier when it's lightly loaded (running in low gear). That's when it sounds like there is a handful of rocks being kicked around inside the motor. When it's running in high gear - it only sounds like one or two rocks.

I'm out of town at the moment (away from my shop), but as I recall the voltages were 228-230 between L1 & L2 and about 242 on the third leg. The confusing part is that the other two motors running off of the converter sound fine.

Is there different styles of windings and/or motor designs that would make a difference when running off a phase converter?

Is this something that I should be concerned about? Will it destroy the motor or is it just annoying?

Joe,

I am very concerned about the noise. Whatever is making it cannot be good for your lathe. The noise is about the only way your machine can tell you something is wrong.

My initial post to this thread suggested the problem may be mechanical, perhaps something in the gear box. Your last response, in which you report the noise decreases with increasing mechanical load, makes me think it could be something mechanical in the gearbox. The type of noise (high pitch staccato) you report is not the kind of thing I usually hear when a phase converter is acting up; those converter trouble noises, whether coming from the load motor or the converter idler, are usually very low pitched and long, drawn out sounds, like an alarm buzzer. They sound BAD, making you want to shut everything off now. With phase balance problems, things get worse with INCREASING mechanical load on the load motor.

The voltages you report above are borderline, and ibewgypsie’s idea still could be what’s causing the noise. In order for me to be satisfied that phase imbalance is not the issue, could you give me the three line CURRENTS going to your lathe under load? If those currents are seriously unbalanced, then electrical phase imbalance is a real possibility, BUT easily fixed with a cheap run capacitor on your lathe motor.

You can measure the currents with a clamp-on type ammeter, such as an Amprobe – very easy to use, with no connections.

There are not different style windings in induction motors which would cause a difference with operation from a phase converter.

Like you, I would love to know from ibewgypsie the make and model of the inverter he refers to.

One final point, which is really ibewgypsie's idea: can you run all three of your machines off the converter at the same time, and see if the noise improves or gets worse? If it improves, phase imbalance is the likely culprit, and you may need a bigger converter.

bnelson

A bigger convertor my be needed alright. If you only have one motor making these noises and you just can't tell wheather it's the motor or the machine, try the motor with the machine(belt or whatever) off and see if the noise is still present.
If you don't get any noise the problem is very possibly mechanical. As has been said you may have a problem with gearing etc. If it makes less noise with more load gears can be very suspect. Good luck.

Thanks for all the input. I guess my hopes of it being a common problem with a simple fix are shot. Anyway, it sounds like a more thorough investigation is in order. I'm on the road alot at the moment so it may take a while, but when I track down the problem I'll let you know what I find.

Joe,

By any chance, you didn't connect the VFD directly to the motor and get the motor leads mixed up? If you have a typical 220/440 motor with 9 leads, getting some swapped will cause the motor to make noise. You might also check to see if something didn't come loose as well.

I have built over 1,100 rotarty phase converters personally in the last 25 years. Sure sounds like the voltage sensing relay is not opening up to take the starting capacitors out of the circuit to me. Find out the problem quickly, or you will fry that motor, Ken.

Joe,

Any luck on your motor noise?

Hi Everybody,
Now that I have been reunited with my machines, I have some more information - if anyone can help.
My line voltages are as follows:
L1-L2 233v
L2-L3 240v
L1-L3 223v

Running currents:
L1 5.4 A
L2 10.0 A
L3 6.2 A

The motor still makes noise with the belts disconnected, so it's not mechanical. The noise also stops immediately when the power is cut, (no noise when the spindle is winding down).
One last note... when the lathe is running and I start the Bridgeport, it really rattles for that fraction of a second when the B-port spindle is coming up to speed.

It seems to be much easier to troubleshoot when your not 800 miles from your equipment. Who woulda guessed??

Thanks,
Joe

hry joe I once ran into a woodworking jointer with similar symptoms- it turned out it was wired 440 while the juice coming in was 220...... surprisingly it started, but it was not happy.

pete

I had a simular problem with my converter when I first hooked it up to my lathe. I have a 5 hp lathe and a 10 hp rotary converter. When starting the lathe the idler motor would growl until the lathe reached it's speed. I found that my by changing the three power leg around to different motor leads the sound went away and the lathe started better. Hope this helps.