Need Help KBAC-29D with 3HP vibration problem

S

smarti1038

Joined
Dec 20, 2010
Messages
6
Hey guys, I need some help trying to figure out a problem with my KBAC-29D and Baldor 3HP (VM3559). When I run at high speed, everything is fine. When I slow it down below 40%, I start to get a lot of vibration and related vibration noises from the motor.

I can’t tell if it’s a physical problem with the motor or coming from frequency issues on the VFD. I have tried adjusting the trimpots. I’ve tried running on 2x. Same issues.

Both the VFD and motor are new, but the motor is old stock. I’ve had it about 6 years and never installed.

I posted a video on YouTube for you guys to see what I’m talking about.

Any help would be appreciated.

Thanks,
Squidlo
 
Almost sounds like bad bearing in the motor.

The baldors I have had run almost silent.
 
Check the voltage on the three phase lines between the VFD and the motor at the motor end (reference ground). Do this when it is making noise. You may have one phase dropping out. If the voltage is low, intermittend or non existant, check the same line between ground and the VFD end. If the voltage is correct there, you have a bad cable or bad connection.

If you are not familiar with electricity, be safe and get someone who is to do the measurements for you!
Jim A.
 
It does sound a bit like a bad bearing, check first - change if you want, make sure the bearing grease is not hardened.


3450RPM ?

Read about "vfd cogging"

trim pot settings can minimize
 
There's a pot adjustment. It's the comp adjustment. It needs to be turned ccw all the way down. I just spent a couple of days trying to figure this out. Disconnect power and take a phillips head screwdriver and turn ccw.
 
DAMNENG said:
Check the voltage on the three phase lines between the VFD and the motor at the motor end (reference ground). Do this when it is making noise. You may have one phase dropping out. If the voltage is low, intermittend or non existant, check the same line between ground and the VFD end. If the voltage is correct there, you have a bad cable or bad connection.

If you are not familiar with electricity, be safe and get someone who is to do the measurements for you!
Jim A.
Click to expand...

Depending on if he has a TRMS meter or not, he may not be able to check the voltage output of the VFD, unless there's nothing at all on one of the legs, which will just show as zero. That said, since the motor starts without manual intervention, I wouldn't suspect a dropped phase. Still a good idea to check that all the connections are right and tight, however.

To the OP:
I'm gonna assume the motor is wired for 220VAC, and not 480VAC, correct?

With the VFD OFF, turn the motor shaft by hand a full 360 degrees. Do you feel any rough spots or catches? Will it free spin on it's own for more than a few revolutions if you give it a quick spin? You might try taking the fan shroud off and make sure nothing is rubbing there. I've had motors that sounded the the bearings were roached, only to find that there was a small ding in the fan shroud.

Lastly, try changing the CT (constant torque) jumper to VT (variable torque) and see if the noise goes away.
 
Thanks for all of the inputs. I tried all of suggestions. As Drew mentioned, I changed J10 from constant torque (CT) to variable torque (VT) and the noise and vibration went away. However, with j10 set to VT, it is very easy to stop the motor. Is this normal?

Another point, while in the CT setting and making noise, the voltage readings at the motor would bounce around rapidly +/-30 volts at the lower speeds. At high speeds the voltage was constant.

With the j10 jumper set to VT, the voltage is constant at all speeds.
 
It is probably still bouncing around in the CT mode at the higher speeds, you just can't see it because it averages out. Sort of like looking at a series of photos vs looking at a video. The video is the same as the photos, just at a speed you can't see them individually. IIRC, in CT, the power is delivered at full value in On and OFF segments.

The effect is called cogging. It gets its name from the graph or oscilloscope image of the waveform … which looks like flat topped cog teeth. When the VFD is set to a mode that creates a more sinus curve, the sound and feel isn't as bad.
 
smarti1038 said:
Thanks for all of the inputs. I tried all of suggestions. As Drew mentioned, I changed J10 from constant torque (CT) to variable torque (VT) and the noise and vibration went away. However, with j10 set to VT, it is very easy to stop the motor. Is this normal?

Another point, while in the CT setting and making noise, the voltage readings at the motor would bounce around rapidly +/-30 volts at the lower speeds. At high speeds the voltage was constant.

With the j10 jumper set to VT, the voltage is constant at all speeds.
Click to expand...

I had a suspicion the CT to VT would fix it. I have a similar vibration at lower frequencies (say 0-15) on my Kbac-27d when it's jumpered to CT. Unfortunately, like you said, when it's on VT, you can stop the motor on low speeds just by looking at it, which for a belt grinder (vs, say a fan) is not very practical. I've learned to just live with the lower speed cogging, but it's not quite as bad as what you're experiencing.

Just out of curiousity, is your "Boost" jumper at "fixed" or "adjustable"? I assume your FREQ jumper also matches that of the motor?
You might also be able to reduce the cogging effect by increasing your minimum speed pot. Just for reference, here are the recommended adjustments for the trim pots:

MAX: Turn all the way clock wise. MIN: Approximately set at the 9:00 position and adjust to personal preference. This controls the grinder's speed when the "% Speed Knob" on the front cover of the VFD is turned to 0%. It is recommended to set this so that the grinder is still moving slowly as a reminder to the operator that the unit is in the "run" mode until the switch is placed in the "stop" position. ACCEL: Approximately set at the 9:00 position and adjust to personal preference. This controls how fast the grinder accelerates up to speed when started from rest. If this is set too aggressively, the controller will shut-off with a fault alarm. Turning the Pot clockwise increases the amount of time for the grinder to accelerate to full speed. DECEL: Approximately set at the 9:00 position and adjust to personal preference. This controls how fast the VFD brakes the grinder to a full stop when the Run/Stop switch is placed in the Stop position. If this is set too aggressively, the controller will shut-off with a fault alarm. Turning the Pot clockwise increases the amount of time for the grinder to stop. BOOST: Do not use this feature with the KMG and ignore this adjustment. CL: Turn all the way Clockwise. JOG: Do not use this feature with the KMG and ignore this adjustment. COMP: Turn all the way Counter Clockwise.
 
You must log in or register to reply here.
Back
Top