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30 T overhead crane with a binding problem

Onil Fillion

New Member
Joined
Mar 31, 2022
Messages
3
Location
Manitoba, Canada
Morning guys. Need some help / advice.

I have a Larco 30 T crane with a binding problem. It all has to do with the bridge drive brakes. It used to happen often after you release the paddle on the Cattron remote; the crane coasts for a short distance and then binds on the tracks. The tracks are perfectly straight; we recently had them straighten, surveyed and approved.

We know it it's one of the bridge drive's brake that is locking in prematurely. Or, when the brakes are suppose to kick in after 15 seconds or so of coasting one brake engages like they should and the other doesn't. No faults in the Magnetek drive. Both drive motor brakes are adjusted the same at approx. 0.015" gap. So, I figured it must be the contactor(s) sticking or something and yes, they were in really bad condition so we replaced them; didn't make a difference. The magnet coils in the motors either work or not and they do so I then thought of the rectifiers in the SEW motors as they control the brakes. We installed new rectifiers in both motors and it solved the problem. No more binding until last night; it started doing it again. Ran great for 1 week. This crane runs pretty much 24/5 non-stop.

Not sure yet if the new rectifiers are defective again but if they are, what is causing them to fail? There's only one Magnetek drive that control both contactors / motors. Could the problem be something else? o_O
 

cranesafety

Active Member
Joined
Apr 17, 2017
Messages
26
Location
Pittsburgh, PA
Is the problem limited to any localized area of the runway? If so, disable the brakes from the motors and test bridge through that localized area. Observe the bridge wheels and how the wheel flanges interact with the rail. Never assume that because rails are "perfectly straight", they are within CMAA specifications for alignment. These specifications include tolerances for span, straightness, elevation and transverse elevation, all of which can cause crane skew and binding.

As for checking the motor brake circuit: First verify all is wired accordingly to the print as designed.

Verify ac voltage input to the motors (if two-speed motors, verify voltage at high and low speed windings) is within prescribed values across all three phases. Verify ac input voltage to rectifiers in each motor.

Verify dc voltage output at each rectifier. If economizing type rectifiers, verify initial voltage and holding voltage is reduced after brake opens. If economizing type remain at the initial high voltage, the economizing circuit has failed and the initial (high voltage) could cause the brake coil to fail.

Check the wiring from the rectifiers to the brake coils for wear or damage. Especially anywhere the wiring is exposed, near shafts or places rubbing might occur. A short to ground in these wires could cause the rectifier to fail.

Note: 15 seconds of "coasting" seems excessive. Are you referring to the brake off time-delay? Usually, this off-time delay can be adjusted in the drive. If properly adjusted, the drive should permit the bridge motors to ramp down and come to a stop within a few feet of the point when the controller is returned to neutral, the brakes should then set within a second or two.
 

Onil Fillion

New Member
Joined
Mar 31, 2022
Messages
3
Location
Manitoba, Canada
Turns out the problem is with the Magnetek drives. They don't always run in sync. They are outdated so I will replace them both.
Is the problem limited to any localized area of the runway? If so, disable the brakes from the motors and test bridge through that localized area. Observe the bridge wheels and how the wheel flanges interact with the rail. Never assume that because rails are "perfectly straight", they are within CMAA specifications for alignment. These specifications include tolerances for span, straightness, elevation and transverse elevation, all of which can cause crane skew and binding.

As for checking the motor brake circuit: First verify all is wired accordingly to the print as designed.

Verify ac voltage input to the motors (if two-speed motors, verify voltage at high and low speed windings) is within prescribed values across all three phases. Verify ac input voltage to rectifiers in each motor.

Verify dc voltage output at each rectifier. If economizing type rectifiers, verify initial voltage and holding voltage is reduced after brake opens. If economizing type remain at the initial high voltage, the economizing circuit has failed and the initial (high voltage) could cause the brake coil to fail.

Check the wiring from the rectifiers to the brake coils for wear or damage. Especially anywhere the wiring is exposed, near shafts or places rubbing might occur. A short to ground in these wires could cause the rectifier to fail.

Note: 15 seconds of "coasting" seems excessive. Are you referring to the brake off time-delay? Usually, this off-time delay can be adjusted in the drive. If properly adjusted, the drive should permit the bridge motors to ramp down and come to a stop within a few feet of the point when the controller is returned to neutral, the brakes should then set within a second or two.
 

cranesafety

Active Member
Joined
Apr 17, 2017
Messages
26
Location
Pittsburgh, PA
Ok, I was under the impression that only one drive was controlling both motors. Sounds like you have a handle on things.

If you have any input and flexibility in the purchase, I highly recommend replacing with Power Electronics drives. They are very robust and user friendly with great tech support and online video demonstrations. Not a salesman but a tech with field experience using their products. Best of luck to you.

PE® Home - Power Electronics® International, Inc.® (peinfo.com)
 

Onil Fillion

New Member
Joined
Mar 31, 2022
Messages
3
Location
Manitoba, Canada
Better then Magnetek in your opinion? I've never heard of them but I will look them up. Seeing how we have 6 overhead cranes, bossman might not want to change over but I will investigate.
Thanks for the info.
Ok, I was under the impression that only one drive was controlling both motors. Sounds like you have a handle on things.

If you have any input and flexibility in the purchase, I highly recommend replacing with Power Electronics drives. They are very robust and user friendly with great tech support and online video demonstrations. Not a salesman but a tech with field experience using their products. Best of luck to you.

PE® Home - Power Electronics® International, Inc.® (peinfo.com)
 
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